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Purpose: To analyze the efficacy and safety of topography-guided photorefractive keratectomy (TG-PRK) to treat irregular astigmatism after corneal transplantation., Methods: This was a retrospective observational case series. Eyes with irregular astigmatism after penetrating keratoplasty treated with TG-PRK (Allegretto Wave Eye-Q) with the topography-guided customized ablation treatment protocol were included. All treatments had been planned to correct the topographic irregularities, as well as to reduce the refractive error after neutralizing the induced refractive change. Clinical records, treatment plan, and the examinations performed were reviewed and the following data were collected: corrected and uncorrected distance visual acuities; manifest refraction; topographic parameters, and corneal endothelial cell count., Results: We included 31 eyes [30 patients; mean age 45.0 ± 13.4 (SD) years]. At the last postoperative follow-up (mean 9.2 ± 8.2 months), we observed a significant improvement in corrected (P = 0.001) and uncorrected distance visual acuities (P < 0.001). There was a gain of ≥1 uncorrected distance visual acuity line in 96.8% (n = 30) of the eyes. Similarly, the refractive parameters also improved (cylinder P < 0.001; spherical equivalent P = 0.002). At the last visit, 54.8% (n = 17) of the patients presented a spherical equivalent of ±1 D. The 3-mm topographic irregularity also decreased significantly (P < 0.001). There was no significant variation of the corneal endothelial cell count., Conclusions: This is the largest case series of TG-PRK to treat irregular astigmatism in postcorneal transplantation eyes. Our results confirm that TG-PRK is an efficient treatment, associated with significant improvements of both visual acuity and refractive parameters.

Objective: To evaluate changes in corneal astigmatism in patients undergoing orbital decompression surgery., Methods: This retrospective, non randomized comparative study involved 42 eyes from 21 patients with thyroid ophthalmopathy who underwent orbital decompression surgery between September 2011 and September 2014. The 42 eyes were divided into three groups: control (9 eyes), two-wall decompression (25 eyes), and three-wall decompression (8 eyes). The control group was defined as the contralateral eyes of nine patients who underwent orbital decompression surgery in only one eye. Corneal topography (Orbscan II), Hertel exophthalmometry, and intraocular pressure were measured at 1 month before and 3 months after surgery. Corneal topographic parameters analyzed were total astigmatism (TA), steepest axis (SA), central corneal thickness (CCT), and anterior chamber depth (ACD)., Results: Exophthalmometry values and intraocular pressure decreased significantly after the decompression surgery. The change (absolute value (|x|) of the difference) in astigmatism at the 3 mm zone was significantly different between the decompression group and the controls (p = 0.025). There was also a significant change in the steepest axis at the 3 mm zone between the decompression group and the controls (p = 0.033). An analysis of relevant changes in astigmatism showed that there was a dominant tendency for incyclotorsion of the steepest axis in eyes that underwent decompression surgery. Using Astig PLOT, the mean surgically induced astigmatism (SIA) was 0.21±0.88 D with an axis of 46±22°, suggesting that decompression surgery did change the corneal shape and induced incyclotorsion of the steepest axis., Conclusions: There was a significant change in corneal astigmatism after orbital decompression surgery and this change was sufficient to affect the optical function of the cornea. Surgeons and patients should be aware of these changes.

Preoperative and postoperative wavefront aberrations of 73 myopic eyes with small incision lenticule extraction surgery are analyzed in this paper. Twenty-eight postoperative individual eye models are constructed to investigate the visual acuity (VA) of human eyes. Results show that in photopic condition, residual defocus, residual astigmatism, and higher-order aberrations are relatively small. 100% of eyes reach a VA of 0.8 or better, and 89.3% of eyes reach a VA of 1.0 or better. In scotopic condition, the residual defocus and the higher-order aberrations are, respectively, 1.9 and 8.5 times the amount of that in photopic condition, and the defocus becomes the main factor attenuating visual performance.

Objective: To develop corneal morphometric models with refractive error in excimer laser surgery., Method: A prospective-longitudinal study was conducted on 78 patients (151 eyes) using the LASIK surgical technique, and 56 patients (111 eyes) with myopic astigmatism using ESIRIS (Schwind-Germany) equipment with pendulous microkeratome. The results were analyzed using descriptive statistics. A NIDEK Confoscan microscope was used to obtain and study the images., Results: After LASIK treatment 84.3% of the variations in epithelium thickness variations were due to the magnitude of refractive error and the epithelium thickness before LASIK treatment. More than two-thirds (68.8%) of the variations in keratocyte density variations in posterior flap and 48.2% of the variations in the anterior retroablation zone were due to the magnitude of the refractive error. Variations of 90% were found in the corneal thickness after LASEK, which were due to the magnitude of the refractive error before LASEK., Conclusions: Predictive models reveal that morphometrical variations depend of the magnitude of the refractive error. These models are very important in the selection of patient for refractive surgery, and also for the specific technique to use., (Copyright © 2013 Sociedad Española de Oftalmología. Published by Elsevier España, S.L.U. All rights reserved.)

Purpose: The primary objective of the study was to explore the statistics of ocular higher-order aberrations in a population of primary and secondary school children., Methods: A sample of 557 children aged 10-15 years were selected from two primary and two secondary schools in Heraklion, Greece. Children were classified by age in three subgroups: group I (10.7±0.5 years), group II (12.4±0.5 years) and group III (14.5±0.5 years). Ocular aberrations were measured using a wavefront aberrometer (COAS, AMO Wavefront Sciences, USA) at mesopic light levels (illuminance at cornea was 4lux). Wavefront analysis was achieved for a 5mm pupil. Statistical analysis was carried out for the right eye only., Results: The average coefficient of most high-order aberrations did not differ from zero with the exception of vertical (0.076μm) and horizontal (0.018μm) coma, oblique trefoil (-0.055μm) and spherical aberration (0.018μm). The most prominent change between the three groups was observed for the spherical aberration, which increased from 0.007μm (SE 0.005) in group I to 0.011μm (SE 0.004) in group II and 0.030μm (SE 0.004) in group III. Significant differences were also found for the oblique astigmatism and the third-order coma aberrations., Conclusions: Differences in the low levels of ocular spherical aberration in young children possibly reflect differences in lenticular spherical aberration and relate to the gradient refractive index of the lens. The evaluation of spherical aberration at certain stages of eye growth may help to better understand the underlying mechanisms of myopia development., (Copyright © 2014 Spanish General Council of Optometry. Published by Elsevier Espana. All rights reserved.)

Purpose: The aim of this study was to determine intertest variability of measurements taken by the Pentacam tomographer in eyes with keratoconus., Methods: Three Pentacam measurements with 1-minute intervals were taken from 101 eyes (81 keratoconus and 20 controls) from 57 patients (47 keratoconus and 10 controls) by the same examiner and under the same conditions. Keratoconus eyes were divided into 3 subgroups based on topographic astigmatism (TA). Variability in astigmatism, mean keratometry, central corneal thickness, and fixation values were compared within the patient subgroups versus normal controls., Results: Variability of all studied parameters (astigmatism, mean keratometry, central corneal thickness, and fixation values) increased with increasing TA in patients with keratoconus., Conclusions: Pentacam measurements show increased variability in patients with keratoconus. The degree of variability correlates with TA.

Objective: To observe the change of teenagers with short-time and long-time orthokeratology discontinuation, including diopters, corneal curvature, corneal topography, axial length, and central corneal thickness, and to investigate the refractive correction methods after long-time orthokeratology discontinuation., Methods: Retrospective study. A total of 141 patients (257 eyes) with a history of wearing and discontinuing wearing orthokeratology lenses in our center were collected. According to the spherical equivalent diopters, the patients were divided into two groups (< or = -4.00 D for group I and -4.00 D for group II). Each group was further divided into two sub-groups by the discontinuation time (1 to 3 months for sub-group A and more than 3 months for sub-group B). Four sub-groups were named as I A, II A, I B, and II B. Some optical examinations were performed for the patients before orthokeratology lens wearing and after orthokeratology discontinuation, such as refraction, corneal curvature, corneal topography, corneal endothelial cells, axial length, and central corneal thickness measurement. The refractive correction methods used by patients who had long-term orthokeratology discontinuation were recorded. The observed data were analyzed with paired t-test and one-way ANOVA by SPSS16., Results: The statistically significant changes (t = 3.222, 3.404, 3.141, 5.012, P < 0.05) of spherical diopter values were (-0.31 +/- 0.58) D, (-0.48 +/- 0.68) D, (-0.35 +/- 0.65) D, and (-0.57 +/- 0.58) D for groups IA, IB, IIA, and IIB, respectively. astigmatism of the four sub-groups had no significant change (P > 0.05) The average annual spherical growth was (-0.08 +/- 0.17) D, (-0.12 +/- 0.17) D, (-0.07 +/- 0.19) D, and (-0.15 +/- 0.16) D, respectively, for the four sub-groups, and there was no statistically significant difference among them (F = 1.180, P > 0.05). Compared to the state before wearing orthokeratology lenses, the corneal curvature measured by an autorefractor was statistically different for groups I A and I A, but not statistically different for groups I B and II B. For the long-time discontinuation groups, only the SRI of the corneal topography had a statistically significant decrease compared to the value before wearing orthokeratology lenses, and others had no significant change. The average annual increase of axial length was (0.22 +/- 0.16) mm and (0.16 +/- 0.10) mm for groups IA and IB, respectively, and the increase was statistically significant (P < 0.05), but there was no significant difference between the two sub-groups (F = 1.908, P > 0.05). The central corneal thickness had no significant change (t = 1.971, 2.017, P > 0.05). The rates of the refractive correction methods after long-time discontinuation were 36.7%, 22.4%, 22.4%, 12.4%, and 6.1% for spectacles, rigid gas permeable contact lenses, soft contact lenses, either spectacles or soft contact lenses, and refractive operations, respectively., Conclusion: The corneal morphology and central corneal thickness returned to the original after three months of discontinuation of orthokeratology. The myopia had no significant growth after discontinuation, and there was no significant difference between low to moderate and relatively high myopia.

To identify genetic variants associated with refractive astigmatism in the general population, meta-analyses of genome-wide association studies were performed for: White Europeans aged at least 25 years (20 cohorts, N = 31,968); Asian subjects aged at least 25 years (7 cohorts, N = 9,295); White Europeans aged <25 years (4 cohorts, N = 5,640); and all independent individuals from the above three samples combined with a sample of Chinese subjects aged <25 years (N = 45,931). Participants were classified as cases with refractive astigmatism if the average cylinder power in their two eyes was at least 1.00 diopter and as controls otherwise. Genome-wide association analysis was carried out for each cohort separately using logistic regression. Meta-analysis was conducted using a fixed effects model. In the older European group the most strongly associated marker was downstream of the neurexin-1 (NRXN1) gene (rs1401327, P = 3.92E-8). No other region reached genome-wide significance, and association signals were lower for the younger European group and Asian group. In the meta-analysis of all cohorts, no marker reached genome-wide significance: The most strongly associated regions were, NRXN1 (rs1401327, P = 2.93E-07), TOX (rs7823467, P = 3.47E-07) and LINC00340 (rs12212674, P = 1.49E-06). For 34 markers identified in prior GWAS for spherical equivalent refractive error, the beta coefficients for genotype versus spherical equivalent, and genotype versus refractive astigmatism, were highly correlated (r = -0.59, P = 2.10E-04). This work revealed no consistent or strong genetic signals for refractive astigmatism; however, the TOX gene region previously identified in GWAS for spherical equivalent refractive error was the second most strongly associated region. Analysis of additional markers provided evidence supporting widespread genetic co-susceptibility for spherical and astigmatic refractive errors.

Background: To evaluate the refractive outcomes for the correction of low to moderate astigmatism up to 1 year following small incision lenticule extraction (SMILE) surgery., Methods: This retrospective study enrolled 98 eyes from 98 patients who underwent SMILE surgery for the correction of myopia and astigmatism. Only right eyes were included in this study to avoid the bias of orientation errors. The vector method was used to analyze the outcomes of astigmatism at 1 month, 6 months and 12 months after the procedure, including the double-angle plots, correction index (CI), index of success (IOS), angle of error (AofE) and magnitude of error (MofE). The effectiveness, safety, stability and predictability were also investigated during the 12-month follow-up., Results: The preoperative cylinder ranged from -2.75 D to -0.25 D (average of -0.90±0.68 D), and the mean postoperative cylinder values were -0.24±0.29 D, -0.24±0.29 D, and -0.20±0.27 D at 1 month, 6 months, and 12 months, respectively. The mean astigmatism in vector form was -0.14 D×27.19° at 1 month, -0.13 D×27.29° at 6 months, and -0.10 D×28.63° at 12 months after surgery. The CI was 1.00±0.32 and IOS was 0.29±0.44 at the 12-month follow-up. Significant negative correlations were found between the CI and absolute target induced astigmatism (TIA) value, and positive correlations were found between the IOS and absolute AofE value (P<0.05). The MofE was limited within ±1.00 D at the 12-month follow-up. Fifty-six eyes (57.1%) gained one line in corrected distance visual acuity (CDVA) and five eyes (5.1%) gained two lines. There were no significant differences observed in the refractive outcomes among time points., Conclusions: SMILE surgery was effective and safe in correcting low to moderate astigmatism, and stable refractive outcomes were observed at the long-term follow-up. The undercorrection of astigmatism could possibly be influenced by attempted astigmatism correction preoperatively, the axis rotation during the surgery or wound healing postoperatively. This study suggested that nomograms should be adjusted in correcting astigmatism with SMILE surgery.

Keratoconus (KC) is the most common cornea ectatic disorder. It is characterized by a cone-shaped thin cornea leading to myopia, irregular astigmatism, and vision impairment. It affects all ethnic groups and both genders. Both environmental and genetic factors may contribute to its pathogenesis. This review is to summarize the current research development in KC epidemiology and genetic etiology. Environmental factors include but are not limited to eye rubbing, atopy, sun exposure, and geography. Genetic discoveries have been reviewed with evidence from family-based linkage analysis and fine mapping in linkage region, genome-wide association studies, and candidate genes analyses. A number of genes have been discovered at a relatively rapid pace. The detailed molecular mechanism underlying KC pathogenesis will significantly advance our understanding of KC and promote the development of potential therapies.

Keratoconus is a degenerative disease that affects adolescents and young adults and presents with variable thinning and conical deformation of the corneal apex. The resultant irregular astigmatism can progress to levels that can significantly affect everyday activities and overall quality of life. Therefore, stopping the progression of the disease is an essential part in managing patients with keratoconus. Corneal collagen cross-linking is a minimally invasive procedure that stiffens the anterior corneal stroma by creating strong covalent bonds between collagen fibrils. Over the past decade, many studies have proved its safety and efficacy in halting keratoconus progression in adults. This review of the literature highlights the growing trend towards using this treatment in pediatric keratoconic patients. In children, keratoconus tends to be more severe and fast progression is often encountered requiring closer follow-up intervals. Standard cross-linking shows comparable results in children with a good safety-efficacy profile during follow-up periods of up to three years. Further research is needed to standardize and evaluate transepithelial and accelerated cross-linking protocols as these could be of tremendous help in a population where cooperation and compliance are major issues.

Purpose: To illustrate the concept of using a stromal surface topography-guided procedure for therapeutic repair after a complication following primary laser refractive surgery., Methods: One case example of therapeutic retreatment for short nasal flap after primary LASIK performed in September 2000 is presented. The Artemis very high-frequency digital ultrasound arc-scanner (Arc-Scan, Inc., Morrison, CO) was used to obtain layered corneal thickness including epithelial thickness profile. Corneal front surface elevation was measured with the Orbscan II (Bausch & Lomb, Salt Lake City, UT). Stromal surface height was then calculated by subtracting epithelial thickness data from corneal front surface elevation data and used to calculate the ablation profile applied to the eye. The treatment was performed using the Ultralink system (ArcScan, Inc.), linking the ultrasound corneal thickness data with the Technolas 217c laser (Bausch & Lomb). Postoperative data were available at 30 days and 13 years., Results: One month after treatment, the epithelial thickness map demonstrated that the difference in thickness between the thinnest and thickest points located 2.5-mm nasally was reduced by 26 µm (from 56 to 30 µm). The axial difference map demonstrated an increase in corneal curvature of approximately 4 diopters where the cornea was the flattest nasally, thereby reducing the corneal asymmetry. The anterior elevation map also showed a reduced depression nasally. The patient reported significant improvement of her night vision., Conclusions: This case example of stromal surface topography-guided treatment demonstrated a significant reduction in the irregularity of the stromal surface and an improvement in the topography, and the visual quality. Stromal surface topography-guided ablation might become the tool of the future for therapeutic repairs because it offers advantages over the current alternative of transepithelial phototherapeutic keratectomy., (Copyright 2015, SLACK Incorporated.)

Purpose: To evaluate changes in anterior corneal topography and higher-order aberrations (HOA) after 14-days of rigid gas-permeable (RGP) contact lens (CL) wear in keratoconus subjects comparing two different fitting approaches., Methods: Thirty-one keratoconus subjects (50 eyes) without previous history of CL wear were recruited for the study. Subjects were randomly fitted to either an apical-touch or three-point-touch fitting approach. The lens' back optic zone radius (BOZR) was 0.4mm and 0.1mm flatter than the first definite apical clearance lens, respectively. Differences between the baseline and post-CL wear for steepest, flattest and average corneal power (ACP) readings, central corneal astigmatism (CCA), maximum tangential curvature (KTag), anterior corneal surface asphericity, anterior corneal surface HOA and thinnest corneal thickness measured with Pentacam were compared., Results: A statistically significant flattening was found over time on the flattest and steepest simulated keratometry and ACP in apical-touch group (all p<0.01). A statistically significant reduction in KTag was found in both groups after contact lens wear (all p<0.05). Significant reduction was found over time in CCA (p=0.001) and anterior corneal asphericity in both groups (p<0.001). Thickness at the thinnest corneal point increased significantly after CL wear (p<0.0001). Coma-like and total HOA root mean square (RMS) error were significantly reduced following CL wearing in both fitting approaches (all p<0.05)., Conclusion: Short-term rigid gas-permeable CL wear flattens the anterior cornea, increases the thinnest corneal thickness and reduces anterior surface HOA in keratoconus subjects. Apical-touch was associated with greater corneal flattening in comparison to three-point-touch lens wear., (Copyright © 2014 Spanish General Council of Optometry. Published by Elsevier Espana. All rights reserved.)

Objective: To explore the distribution of relational corneal thickness parameters including central corneal thickness (CCT), thinnest pachymetry (TP), cornea thickness spatial profile (CTSP), percentage thickness increase (PTI), pachymetric progression index (PPI) and Ambrósio's relational thickness (ART) in the normal population, and their relationships with corneal astigmatism and curvature., Methods: A total of 1 203 eyes from 1 203 normal outpatients were enrolled in this cross-sectional study. The data information of CCT, TP, CTSP, PTI, PPI-max, PPI-min, PPI-ave, axes of PPI-max and PPI-min, ART-max and ART-ave was collected from Pentacam HR for the subsequent analysis of their distribution. Astigmatism, astigmatism axis (AA), and keratometry (K) including Km and Kmax were also collected to explore their relationships with relational thickness parameters., Results: The mean values for CCT and TP were (547.20 ± 31.441) µm and (543.26 ± 31.271) µm, respectively. The mean values for CTSP-2, CTSP-4, CTSP-6 and CTSP-8 were (552.11 ± 31.654) µm, (580.72 ± 32.919) µm, (632.11 ± 34.738) µm and (711.80 ± 37.880) µm, respectively. PTI-2, PTI-4, PTI-6 and PTI-8 were (1.67 ± 0.471)%, (6.89 ± 0.945)%, (16.37 ± 1.996)% and (31.10 ± 3.652)%. PPI-max, PPI-min and PPI-ave were 1.222 ± 0.175, 0.733 ± 0.138 and 0.994 ± 0.123. The axes of PPI-max and PPI-min were 230.74 ± 104.862 and 159.81 ± 62.292. ART-max and ART-ave were (454.940 ± 78.506)µm and (556.140 ± 86.492)µm. CCT, TP, PPI and ART were found to have a weak but significant correlation with Kmax-front, Km-front and Km-back. PPI and ART were also found to weakly correlate with Astig-back. The converted astigmatism axis was found to correlate with the axes of PPI-max (rs = -0.125, P = 0.000) and PPI-min (rs = 0.613, P = 0.000)., Conclusions: The front and back curvatures and the back astigmatism correlate with the distribution of corneal thickness, while the front astigmatism does not correlate with it. The front astigmatism axis tends to distribute coincidently with PPI-min axis.

Objective: To assess refractive and biometric changes 1 week after discontinuation of lens wear in subjects who had been wearing orthokeratology (OK) contact lenses for 2 years., Methods: Twenty-nine subjects aged 6 to 12 years and with myopia of -0.75 to -4.00 diopters (D) and astigmatism of ≤1.00 D participated in the study. Measurements of axial length and anterior chamber depth (Zeiss IOLMaster), corneal power and shape, and cycloplegic refraction were taken 1 week after discontinuation and compared with those at baseline and after 24 months of lens wear., Results: A hyperopic shift was found at 24 months relative to baseline in spherical equivalent refractive error (+1.86±1.01 D), followed by a myopic shift at 1 week relative to 24 months (-1.93±0.92 D) (both P<0.001). Longer axial lengths were found at 24 months and 1 week in comparison to baseline (0.47±0.18 and 0.51±0.18 mm, respectively) (both P<0.001). The increase in axial length at 1 week relative to 24 months was statistically significant (0.04±0.06 mm; P=0.006). Anterior chamber depth did not change significantly over time (P=0.31). Significant differences were found between 24 months and 1 week relative to baseline and between 1-week and 24-month visits in mean corneal power (-1.68±0.80, -0.44±0.32, and 1.23±0.70 D, respectively) (all P≤0.001). Refractive change at 1 week in comparison to 24 months strongly correlated with changes in corneal power (r=-0.88; P<0.001) but not with axial length changes (r=-0.09; P=0.66). Corneal shape changed significantly between the baseline and 1-week visits (0.15±0.10 D; P<0.001). Corneal shape changed from a prolate to a more oblate corneal shape at the 24-month and 1-week visits in comparison to baseline (both P≤0.02) but did not change significantly between 24 months and 1 week (P=0.06)., Conclusions: The effects of long-term OK on ocular biometry and refraction are still present after 1-week discontinuation of lens wear. Refractive change after discontinuation of long-term OK is primarily attributed to the recovery of corneal shape and not to an increase in the axial length.

Purpose: To identify corneal epithelial- and stromal-thickness distribution patterns in keratoconus using spectral-domain optical coherence tomography (SD-OCT)., Patients and Methods: We analyzed SD-OCT findings in 20 confirmed cases of keratoconus (group 1) and in 20 healthy subjects with corneal astigmatism ≥ 2 D (group 2). Epithelial and stromal thicknesses were measured at 11 strategic locations along the steepest and flattest meridians, previously located by corneal topography. Vertical mirrored symmetry superimposition was used in the statistical analysis., Results: The mean maximum keratometry measurements in groups 1 and 2 were 47.9 ± 2.9 D (range, 41.8-52.8) and 45.6 ± 1.1 D (range, 42.3-47.5), respectively, with mean corneal cylinders of 3.3 ± 2.2 D (range, 0.5-9.5) and 3.6 ± 1.2 D (range, 2.0-6.4), respectively. The mean epithelial thickness along the steepest meridian in group 1 was the lowest (37.4 ± 4.4 µm) at 1.2 mm inferotemporally and the highest (59.3 ± 4.4 µm) at 1.4 mm supranasally from the corneal vertex. There was only a small deviation in thickness along the steepest meridian in group 2, as well as along the flattest meridians in both groups. The stromal thickness distribution in the two groups was similar to the epithelial, while the stromal thickness was generally lower in group 1 than in group 2., Conclusions: SD-OCT provides details about the distribution of corneal epithelial and stromal thicknesses. The epithelium and stroma in keratoconic eyes were thinner inferotemporally and thicker supranasally compared with control eyes. The distribution pattern was more distinct in epithelium than in stroma. This finding may help improve the early diagnosis of keratoconus., Trial Registration: ClinicalTrials.gov NCT02023619.

Background: No study to date has looked into the relationship between ocular biometrics with anisometropia exclusively; therefore, the purpose of this study was to determine the relationship between anisometropia and ocular biometrics., Methods: In a cross-sectional study with multistage cluster sampling, 6311 people in the 40-64-year-old age group from the population of Shahroud, Iran, were selected. Of these, 5190 people participated in the study. For all participants, tests for visual acuity, cycloplegic and non-cycloplegic refraction, slit lamp test and fundoscopy were performed. All participants underwent biometric examinations using the Allegro Biograph (WaveLight AG, Erlangen, Germany)., Results: Asymmetry of axial length, corneal power, vitreous chamber depth, anterior chamber depth, lens thickness and lens power were significantly more among participants who were anisometropic than those who were non-anisometropic. The correlation of anisometropia with axial length asymmetry was 0.735, 0.273 with corneal power, 0.183 with anterior chamber depth and 0.311 with lens power (p<0.001). In a multiple linear regression model, anisometropia was found to have significant associations with axial length asymmetry (standard coefficient (SC)=0.905), corneal power asymmetry (SC=0.350), lens power asymmetry (SC=0.454), nuclear opacity asymmetry (SC=0.074) and age (SC=0.28) (R(2)=85.1%). According to the linear regression model, corneal power had the strongest association with anisoastigmatism., Conclusions: Axial length asymmetry has the strongest correlation with anisometropia; nonetheless, other components of ocular biometrics such as corneal power, lens opacity, lens power and anterior chamber depth are related to anisometropia as well. More than 10% of changes in anisometropia can be explained with changes in factors other than asymmetry of ocular biometrics and lens opacity.

Purpose: To evaluate the changes in posterior corneal surface (Q value and elevation) measured with Pentacam after femtosecond laser assisted Sub-Bowman Keratomileusis (SBK)., Methods: The Q values and elevation of posterior corneal surface were determined in 166 myopic/myopic astigmatism eyes of 88 patients using Scheimpflug imaging (Pentacam; Oculus, Wetzlar, Germany), which estimates asphericity and elevation for several areas of cornea analysed (Q value: 6, 7, 8 and 9 mm; elevation: 2, 4, 6 and 8 mm) before 1 and 3 months after SBK. The correlations between the changes of Q value or elevation and the mean preoperative spherical equivalent (SE), central corneal thickness (CCT), central ablation depth (AD), estimated residual bed thickness (RBT) and RBT/CCT ratio were investigated., Results: Meridian and area differences in Q of posterior surface have been showed. Two major meridians (horizontal/vertical) present the change of significant negative direction before surgery (all p < 0.001), but the alteration of significant positive direction for all post-SBK follow-up visits (all p < 0.05). There was no statistically significant difference in posterior elevation at 2 mm zone (horizontal meridian: p = 0.439; vertical meridian: p = 0.233). Compared with preoperation, minor but significant forward displacements were found in posterior elevation at 4 and 6 mm areas of cornea analyzed (horizontal meridian: all p < 0.001; vertical meridian: p < 0.001, p = 0.024, respectively). However, posterior elevation in two meridians (horizontal/vertical) at 8 mm region was displayed significant backward shift (p = 0.001, p < 0.001, respectively). The Pearson correlation test showed no significant correlation between the changes in the Q values and elevation data in vast majority of areas of cornea analyzed and the SE, CCT, AD, RBT, and RBT/CCT ratio at 1 and 3 months after surgery (all p > 0.05)., Conclusions: The posterior corneal surface showed central flattening and peripheral steepening at early stage post-SBK. To combine the asphericity with the elevation of the posterior corneal surface can overall and accurately understand the posterior corneal shape and its variations after refractive surgery.

Purpose: To evaluate the visual refractive and aberrometric outcomes of laser-assisted in situ keratomileusis (LASIK) surgery for the correction of high mixed astigmatism using a new-generation excimer laser and optimized aspherical profiles., Design: Retrospective interventional case series., Methods: Fifty-two eyes of 36 patients (21-53 years) with primary mixed astigmatism over 3.0 diopters (D) were included. All cases underwent LASIK surgery using the sixth-generation excimer laser Amaris with cyclotorsion control and a femtosecond platform for flap creation. Visual, refractive, corneal topographic, and aberrometric outcomes were evaluated during a 3-month follow-up. Refractive astigmatic changes were analyzed by Alpins method., Results: A significant reduction of refractive sphere and cylinder was observed 3 months postoperatively (P = .001), with an associated improvement of uncorrected distance visual acuity (P = .001). Best-corrected distance visual acuity (CDVA) remained unchanged in 31 eyes (59.6%), while 3 eyes (5.76%) lost 2 lines of CDVA. Fourteen eyes (26.9%) had spherical equivalent (SE) within ±0.5 D of emmetropia and 34 (65.3%) had SE within ±1.0 D of emmetropia. No significant difference was observed when comparing surgically induced and target astigmatism. A significant induction of higher-order aberration attributable to increase of spherical aberration was found (P = .003). Seven eyes (13.4%) required retreatment., Conclusions: LASIK for primary high mixed astigmatism using optimized aspherical profiles and a fast-repetition-rate excimer laser with cyclotorsion control is a safe, effective, and predictable procedure. Induction of higher-order aberrations is still present in the correction of the refraction error of the magnitude included in this study., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Successful surgical treatment of ocular astigmatism requires accurate characterization of both magnitude and axis of the astigmatism. Keratometry and topography are clinically widely used for this measurement; however, their analysis is limited to the anterior corneal surface. Unlike these techniques, optical coherence tomography (OCT) offers the advantage of measuring both the anterior and posterior corneal surface contributions. We present a technique to combine the local curvatures of both surfaces into a single pseudosurface suitable for clinical application. Building on prior work in distributed scanning OCT (DSOCT) to remove corrupting patient motion artifacts, we present the results of a pilot patient study where extracted values of clinical corneal astigmatic power magnitude and direction from DSOCT corneal volumes were comparable to standard clinical measures of corneal astigmatism.

Work remains to be done to understand the origins of ocular aberrations. We analyze lens aberrations of several species with Y-suture branches (bovine, ovine, and porcine) and their relationship with suture distribution. Aberrations are measured in vitro with a point diffraction interferometer in 10 different eyes of each species. The minimum number of Zernike polynomials minimizing the root mean square error of the wavefront is estimated by processing the interferograms. Through this we find significant amounts of astigmatism, coma, spherical aberration, and trefoil in the lenses of the three species. Moreover, we observe a high degree of correlation between the orientation of the lens sutures and the axis of nonrotationally symmetric aberrations. Our results point to lens sutures as the histological origin of the most significant lens aberrations: astigmatism, coma, and trefoil, but we are unable to find a major suture governing all the axes.

Purpose: To objectively determine the effects of pupil size on optical quality parameters in astigmatic eyes using a double-pass instrument., Methods: We examined twenty-two eyes of 22 healthy volunteers (mean age  ±  standard deviation, 27.1 ± 2.8 years) who had no ophthalmic diseases other than refractive errors (manifest cylinder ≤ 0.25 diopters (D)). After we fully corrected cycloplegic refraction, we created with-the-rule astigmatism of 1, 2, and 3 diopters in these eyes and then quantitatively assessed the modulation transfer function (MTF) cutoff frequency and the Strehl2D ratio with 2-, 4-, and 6-mm pupil sizes using the Optical Quality Analysis System., Results: The MTF cutoff frequency and the Strehl2D ratio decreased significantly as the amount of astigmatism increased at each pupil size (P < 0.001 for 2, 4, and 6 mm, analysis of variance). They also decreased significantly with an increase in pupil size at each diopter of astigmatism (P < 0.001 for 0, 1, 2, and 3 D). Multiple comparisons demonstrated a significant difference between measurements made for a 2-mm pupil and for a 6-mm pupil at each diopter of astigmatism (P < 0.001 for 0, 1, 2, and 3 D, Dunnett test) and those made for a 4-mm pupil and for a 6-mm pupil at each diopter of astigmatism (P < 0.001 for 0 D, P < 0.05 1, 2, and 3 D)., Conclusions: Eyes with larger pupils had lower optical quality even when they were astigmatic. It may be necessary to correct the preexisting astigmatism to acquire excellent visual performance, especially in astigmatic eyes with larger pupils.

Purpose: Corneal curvature is a key determinant of the refractive power of the eye. Variants in two genes, FKBP12-rapamycin complex-associated protein 1 (FRAP1) on chromosome 1p36.2 and platelet-derived growth factor receptor alpha (PDGFRA) on chromosome 4q12, have shown genome-wide significant association with normal variation in corneal curvature in a study of subjects of Asian origin. Variants at the PDGFRA locus have also shown genome-wide significant association with corneal astigmatism. Whether these variants influence other ocular parameters such as axial length has yet to be reported. We performed a genome-wide association study for corneal curvature in white European subjects from a population-based birth cohort, with the aim of replicating and extending the above findings., Methods: White European children participating in the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort were examined at age about 15.5 years (95% confidence interval=15.45 to 15.48 years). Radius of corneal curvature and axial eye length were measured with an IOLmaster. DNA samples were genotyped with Illumina HumanHap550 arrays and untyped variants imputed using MACH, with CEU individuals from HapMap release 22, Phase II NCBI B36, Single Nucleotide Polymorphism database 126 as the reference panel. Association between corneal curvature and single nucleotide polymorphism (SNP) genotype was tested, genome-wide, using mach2qtl, with sex as a covariate (n=2023; 46.6% male)., Results: The variant exhibiting the strongest evidence for association with corneal curvature (rs6554163; p=2.8×10(-6)) was located in the same linkage disequilibrium block as the previously discovered PDGFRA variants. Meta-analysis of the current and prior findings enhanced the evidence for association (rs17084051, p=4.5×10(-14)). rs6554163 genotype predicted 1.0% of variation in corneal curvature. In addition, these PDGFRA variants were associated with axial eye length, predicting 0.6% of the normal trait variation (p=5.3×10(-4)). Each copy of the minor allele of variants at the locus also increased the risk of corneal astigmatism in this white European cohort (odds ratio [OR]=1.24, 95% confidence interval=1.07-1.45; p=0.006)., Conclusion: As in Asians, variants at the PDGFRA locus influence corneal curvature (and corneal astigmatism). However, rather than affecting corneal curvature in isolation, this locus influences the size of the eye while maintaining its scaling.

Introduction: Keratometry forms an important component of the biometry for a calculation of the intraocular lens power and selecting a contact lens' parameters., Objective: To investigate the agreement between three different keratometers commonly used in an ophthalmology clinic., Materials and Methods: In this prospective study, keratometry was performed using an IOL Master (IM), a manual keratometer (Man) and a autokeratometer (Top) in twenty five eyes of thirteen volunteer subjects. The average keratometry values and corneal astigmatism (J180 and J45 components) were computed and compared. The agreements between the instruments were analysed using the Bland Altman statistical method. The main outcome measures are average keratometry values and corneal astigmatism., Results: The mean of average keratometry values obtained from the IOL Master, manual keratometry and autokeratometry were 44.388 ± 1.430, 44.297 ± 1.425 and 44.220 ± 1.497 D, respectively. The mean difference in the average keratometry between the instruments were 0.31 ± 0.09 for IM and Man (p = 0.012), 0.14 ± 0.17 for IM and Top (p = less than 0.001) and 0.29 ± 0.77 for Man and Top (p = 0.26). The mean differences in the J180 component of astigmatism were: 0.02 ± 0.11 for IM and Man, 0.02 ± 0.09 for IM and Top, and - 0.01 ± 0.11 for Man and Top. Similarly, for the J45 component, the mean differences were 0.02 ± 0.12 for IM and Man, 0.01 ± 0.13 for IM and Top and - 0.02 ± 0.10 for Man and Top., Conclusion: Average keratometry values obtained from different instruments vary significantly. The IOL Master consistently over-estimated the corneal power compared to the manual and the autokeratometer. All three instruments provided similar estimation of the corneal astigmatism., (© NEPjOPH.)

Purpose: To compare and evaluate the agreement between keratometry readings using three devices: the Pentacam HR, the Orbscan IIz, and the TMS-4 topographer., Methods: In this prospective comparative study, 115 eyes from 115 healthy refractive surgery candidates were sequentially examined using three devices. Fourier analysis was used to evaluate corneal astigmatism in these subjects. The outcome measures comprised steep and flat keratometry readings, corneal astigmatism, the mean keratometry reading, and the J0 and J45 components. Repeated-measures analysis of variance (RM-anova) and Bland-Altman plots with 95% limits of agreement were used to evaluate the difference between measurements., Results: The mean keratometry readings were 43.89 ± 1.51, 43.52 ± 1.48, and 43.79 ± 1.50 D using the TMS-4 topographer, the Orbscan IIz, and the Pentacam HR, respectively (p < 0.001; RM-anova). The mean keratometric astigmatism was 1.27 ± 0.87, 1.20 ± 0.86, and 1.21 ± 0.82 D using the TMS-4 topographer, the Orbscan IIz, and the Pentacam HR, respectively (p = 0.007; RM-anova). The J0 measurements were higher using the TMS-4 topographer compared with the Orbscan IIz (p = 0.021; Bonferroni test). The mean, steep, and flat keratometry data were in better agreement using the TMS-4 topographer and the Pentacam HR. In general, the Orbscan IIz device measured lower values than either the TMS-4 topographer or the Pentacam HR. However, the corneal astigmatism measurements and the J0 component showed the best agreement using the TMS-4 topographer and the Orbscan IIz., Conclusions: The TMS-4 topographer and the Pentacam HR produced similar readings and can be used interchangeably to measure simulated keratometry values in young, healthy eyes. To measure corneal astigmatism, the TMS-4 topographer and the Orbscan IIz produced values that were similar and could be used interchangeably., (Ophthalmic & Physiological Optics © 2012 The College of Optometrists.)

Here we aimed to define keratometric and refractive astigmatism in a series of patients who underwent phacoemulsification, using small corneal incision and implantation of foldable intraocular lenses. Furthermore, we compared keratometric astigmatism and refractive astigmatism of the patients both before and after surgery. We performed a follow-up study of patients with newly diagnosed cataract before and after phacoemulsification surgery. Eighty eyes from 78 patients with a mean age of 62.9 ± 12.03 (32-86) years were studied. Thirty-nine (48.8 %) were male and 41(51.2 %) were female. All subjects underwent 3.5 mm corneal incision with the temporal (75 patients; 94 %) or superior (5 patients; 6 %) approach. The patients were followed for a mean of 74.21 ± 71.25 (30-400) days. Patients had higher values of keratometric measurements after surgery compared to those before surgery [45.81 ± 0.11 (45.06-45.94) vs. 45.2 ± 0.20 (44.6-45.41)] (p < 0.001). There was no significant difference in the keratometric astigmatism, refractive astigmatism and keratometry axis pre- and postoperatively. The mean keratometric astigmatism was 0.9 ± 0.54 (0.00-4.00) diopters (D) preoperatively and 0.93 ± 0.45 (0.00-4.00) D postoperatively (p = 0.444). The keratometric axis was 97.7 ± 9.4 preoperatively and 115 ± 15.8 postoperatively (p = 0.185). Refractive astigmatism was 1.15 ± 0.77 (5-180) with the refractive axis of 89.7 ± 5.89 (5-180) degrees in the follow-up (p = 0.752). Ninety percent of the patients had <1.00 D difference in the keratometric and refractive astigmatism, postoperatively. In conclusion while there is no significant difference in postoperative keratometric and refractive astigmatism in most of the eyes, about 10 % show >1 D difference in these measurements.

Purpose: To evaluate the difference in the spherical aberration (SA) induced by an aspheric and a non-aspheric myopic ablation profile with the MEL80 excimer laser (Carl Zeiss Meditec)., Methods: This was a prospective randomized paired-eye controlled study of 15 patients (30 eyes) who underwent LASIK using the Hansatome microkeratome (160 μm) (Bausch & Lomb) and the MEL80 using a 6 mm optical zone. For each patient, one eye was treated with an aspheric (Aberration Smart Ablation [ASA]) profile and the other eye was treated with a non-aspheric (Tissue Saving Ablation [TSA]) profile, assigned at random. Patients were measured before and 3 months after LASIK with the wavefront supported custom ablation aberrometer (Carl Zeiss Meditec), and SA was measured with an analysis zone of 3 to 7 mm in 0.5 mm intervals. The area under the curve of SA plotted against analysis zone (RAWS) was calculated., Results: The mean spherical equivalent refraction was -2.43 ± 1.53 D for the ASA group and -2.54 ± 1.47 D for the TSA group (p = 0.87). There was a statistically significant increase in SA for an analysis zone of 6.0 to 7.0 mm for the ASA group and for an analysis zone of 4.5 to 7.0 mm for the TSA group. At the 6 mm zone, the increase in SA was 0.032 in the ASA group and 0.069 in the TSA group. The induction of SA per diopter was 0.024 μm/D in the ASA group and 0.035 μm/D in the TSA group. The RAWS parameter increased by 34.8% in the ASA group and 74.4% in the TSA group., Conclusions: There was less induction of SA in myopic LASIK with an aspheric ablation profile than with a non-aspheric ablation profile.

Purpose: To investigate the effect of age on the contributions of the anterior cornea and internal components to ocular aberrations in the peripheral visual field., Methods: Ocular aberrations were measured in 10 young emmetropes and 7 older emmetropes using a modified commercial Hartmann-Shack aberrometer across 42° × 32° of central visual field. Anterior corneal aberrations were estimated from anterior corneal topography using theoretical ray-tracing. Internal aberrations were calculated by subtracting anterior corneal aberrations from ocular aberrations., Results: Anterior corneal aberrations of young subjects were reasonably compensated by the internal aberrations, except for astigmatism for which the internal contribution was small out to the 21° field limit. The internal coma and spherical aberration of the older subjects were considerably smaller in magnitude than those of the young subjects such that the compensation for anterior corneal aberrations was poorer. This can be explained by age-related changes in the lens shape and refractive index distribution., Conclusions: Loss of balance between anterior cornea and internal components of higher order aberrations with increasing age, found previously for on-axis vision, applies also to the peripheral visual field.

The aim of the study was to determine the prevalence, distribution and types of corneal astigmatism in cataract surgery patients in Sibenik County. In this retrospective study, keratometric data on 392 eyes of 202 patients admitted for senile cataract surgery to Sibenik General Hospital from April until June 2011 were collected and statistically analyzed. The median age of our patients was 77 (range 50 to 92) years; there were 91 (45%) men and 111 (55%) women. The measured keratometric values ranged from 36.00 to 47.00 diopter. The median of measured corneal astigmatism was 0.75 diopter cylinders (DCyl), ranging from 0 to 6.12 DCyl. In 150 (38.3%) study eyes, corneal astigmatism was in the physiological range of 0.50 DCyl or less, in 118 (30.1%) eyes it was > 0.50-1.0 DCyl, and in 124 (31.6%) eyes > 1.0 DCyl. Preoperative corneal astigmatism of 1 DCyl or more has a significant influence on postoperative refractive outcome. This imposes the need to consider a possible option for correction of preoperative astigmatism at the time of cataract surgery.

Background: To evaluate the influence of corneal astigmatism (CA) on retinal nerve fiber layer (RNFL) thickness and optic nerve head(ONH) parameters measured with spectral-domain optical coherence tomography (OCT) in high myopes patients before refractive surgery., Methods: Seventy eyes of 35 consecutive refractive surgery candidates were included in this study. The mean age of the subjects was 26.42 ± 6.95 years, the average CA was -1.17 diopters (D; SD 0.64; range -0.2 to-3.3D), All subjects in this study were WTR CA. 34 eyes were in the normal CA group with a mean CA was -0.67 ± 0.28D, 36 eyes were in the high CA group with an average CA of -1.65 ± 0.49D. All subjects underwent ophthalmic examination and imaging with the Cirrus HD OCT., Results: No significant difference was noted in the average cup-to-disk ratio, vertical cup-to-disk ratio and cup volume (all P values > 0.05). Compared with the normal CA group, the high CA group had a larger disc area and rim area, thinner RNFL thickness in the temporal quadrant, and the superotemporal and inferotemporal peaks were farther to the temporal horizon (All P values < 0.05). There were no significant differences between the two groups in global average RNFL thickness, as well as superior, nasal and inferior quadrant RNFL thickness (all P values > 0.05)., Conclusions: The degree of with-the-rule CA should be considered when interpreting ONH parameters and peripapillary RNFL thickness measured by the Cirrus HD OCT., Virtual Slides: The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1148475676881895.

Purpose: To investigate the effect of lens fenestrations on the performance of orthokeratology lenses., Methods: Twenty-two subjects (aged 11 to 31 years) were fitted with identical reverse geometry orthokeratology lenses in the two eyes. One eye was randomly designated to wear a lens with three 0.20 mm fenestrations at 120° intervals placed at the junction of the reverse and alignment curves. The lens for the other eye was not fenestrated. Subjects were reviewed at 1 week, 1 month, 3 months, 6 months, and 1 year after fitting. Data were collected on refraction, visual performance, incidences and severity of corneal staining, lens binding, and corneal pigmented arc., Results: Fifteen subjects achieved full correction in OU. There were no statistically significant differences in refractive and corneal changes, visual performance, incidences and severity of corneal staining and corneal pigmented arc formation between the two eyes. The incidence of lens binding was consistently higher in eyes wearing non-fenestrated lenses but was not statistically significant. Severity of lens binding, however, was statistically significant at the 1-, 3-, 6- and 12-month visits, with the non-fenestrated lenses causing more severe binding., Conclusions: The addition of fenestrations to orthokeratology lenses has no effect on the efficacy of the treatment or outcomes in low to moderate myopic subjects. However, the severity of lens binding is reduced. Fenestrating reverse geometry lenses may be of assistance in cases where lens binding is a problem.

Purpose: To characterize the clinical profile of femtosecond lenticule extraction (FLEx) correlated with ultrastructural analysis of the corneal interface and in vivo real-time intraocular pressure (IOP)., Methods: Prospective clinical case series with experimental studies; consecutive patients underwent FLEx at a single tertiary center over 10 months with postsurgical follow-up of 3 months. The patients were divided into three groups according to spherical equivalence (SE) (A, < -5.0 diopters [D]; B, ≥ -5.00 D and < -9.00 D; and C, ≥ -9.0 D). Twelve human cadaveric eyes analyzed using scanning electron microscopy after receiving FLEx; 40 rabbit eyes received FLEx with in vivo IOP measurements. The main outcome measures were refractive outcomes from study subjects; with corneal interface and IOP in experimental studies., Results: Thirty-three subjects (22 females, 66.7%) underwent FLEx in both eyes (66 eyes). Mean age was 32 years (range, 21 to 46 years). Preoperative mean SE was -5.77 ± 2.04 D with astigmatism of -1.03 ± 0.72 D. There was a slight hyperopic shift (mean SE 0.14 ± 0.53 D); 94% achieved uncorrected visual acuity ≥20/25 3 months postoperatively. Refractive stability was achieved within 1 month (P < 0.001). Ultrastructurally, the smoothness of the corneal interface was independent of ablation depth (mean irregularity scores A, B, C: 8.8 ± 0.6, 10.3 ± 0.4, 8.7 ± 0.6, respectively; P = 0.88). The increase in IOP during FLEx was similar to that in femtosecond (FS)-LASIK, albeit a twofold duration of raised IOP in FLEx (P < 0.001)., Conclusions: These results suggest that FLEx is predictable and effective in treating myopia and myopic astigmatism. Experimental studies support the early clinical results and safety of this procedure.

Management of irregular astigmatism with intracorneal rings segments is an intrastromal additive technique developed initially for myopia but eventually popularized for keratoconus and post LASIK ectasia. ICR's are indicated for rigid contact lens intolerance, as an alternative to corneal transplantation. The mechanism of action is complex and involves biomechanical changes leading to a centering and a flattening of the ectasia. The surgical procedure has become much easier thanks to the use of femtosecond lasers. Individualized implantation strategies, based on each patient's topographic and tomographic pattern, are constantly evolving. Patients' refraction and vision are usually improved in more than 70% of cases. Complications remain very rare. Intracorneal ring segments can often be combined with other types of keratoplasty, usually in a sequential fashion, so as to optimize functional results., (Copyright © 2011 Elsevier Masson SAS. All rights reserved.)

Purpose: The aim was to determine the corneal parameters in low to moderate myopic Chinese children and to investigate the differences in these corneal parameters between male and female subjects., Methods: Refractive errors and corneal parameters were retrieved from subjects who had participated in studies on myopia and astigmatism in 2008 and 2009. Corneal parameters including simulated K (Sim K) and asphericity (Q) at 9.0 mm chord and horizontal visible iris diameter (HVID) were determined for 217 children (112 males and 105 females aged from six to 12 years) using the Medmont E300 topographer., Results: The Q of the corneas was -0.44 ± 0.12 along the flat meridian and -0.22 (-0.70 to 0.63) along the steep meridian. The HVID and Sim K of male subjects were larger and flatter than female subjects. The mean HVID of male and female subjects was 11.3 ± 0.3 mm and 11.1 ± 0.30 mm, respectively. The mean Sim K value in male and female subjects was 7.91 ± 0.24 mm and 7.79 ± 0.21 mm, respectively, along the flat meridian, and was 7.65 ± 0.26 mm and 7.53 ± 0.24 mm, respectively, along the steep meridian., Conclusions: All corneas were prolate elliptical in shape along the flat meridian and the peripheral flattening rate was found to be greater along the flat meridian. A greater flattening rate was observed in the corneas of Chinese children when compared to that of Caucasian children. The Q between male and female subjects was not significantly different. Male subjects tended to have larger HVID and flatter corneas than female subjects., (© 2011 The Authors. Clinical and Experimental Optometry © 2011 Optometrists Association Australia.)

Corneal astigmatism refers to refractive abnormalities and irregularities in the curvature of the cornea, and this interferes with light being accurately focused at a single point in the eye. This ametropic condition is highly prevalent, influences visual acuity, and is a highly heritable trait. There is currently a paucity of research in the genetic etiology of corneal astigmatism. Here we report the results from five genome-wide association studies of corneal astigmatism across three Asian populations, with an initial discovery set of 4,254 Chinese and Malay individuals consisting of 2,249 cases and 2,005 controls. Replication was obtained from three surveys comprising of 2,139 Indians, an additional 929 Chinese children, and an independent 397 Chinese family trios. Variants in PDGFRA on chromosome 4q12 (lead SNP: rs7677751, allelic odds ratio = 1.26 (95% CI: 1.16-1.36), P(meta) = 7.87×10(-9)) were identified to be significantly associated with corneal astigmatism, exhibiting consistent effect sizes across all five cohorts. This highlights the potential role of variants in PDGFRA in the genetic etiology of corneal astigmatism across diverse Asian populations., Competing Interests: The authors have declared that no competing interests exist.

In this work we show a conceptually simple and cheap means by which to improve retinal image quality in fundus cameras. We will explain how to build a low-cost variable astigmatism-correcting device with a pair of identical commercial ophthalmic lenses. We have developed and tested a low order aberration compensation device capable of correcting astigmatism prescriptions up to -8.00 D with no significant addition of higher order aberrations. A theoretical description of the device, calibration, and improvement in retinal images without employing any image restoration technique will be shown.

Background: Laser-assisted in situ keratomileusis (LASIK) has undergone several evolutions since it was first approved by the U.S. Food and Drug Administration. Currently, excimer lasers are approved by the U.S. Food and Drug Administration to treat refractive errors with a standard ablation profile, a wavefront-optimized ablation profile, or a wavefront-guided ablation profile. Wavefront-optimized ablation profiles provide a simple method to precompensate for the expected fourth-order spherical aberration and higher-order astigmatism in the average eye., Case Report: We report a case of a 39-year-old white man, with a high magnitude of mixed astigmatism in the right and left eyes, who was seeking refractive surgical options because he was unable to tolerate contact lenses. The patient underwent bilateral wavefront-optimized LASIK to correct his high degree of astigmatism. Wavefront-guided ablation, as in this patient, can not always be performed because the parameters are not within the allowable treatment profile. Four months after the primary LASIK treatment, the patient underwent a bilateral wavefront-optimized LASIK enhancement for residual astigmatism., Conclusion: This case focuses on the utilization of a wavefront-optimized LASIK treatment profile to eliminate a high magnitude of astigmatic refractive error without inducing higher-order aberrations. Wavefront-guided treatments are not required in most cases but should be considered if the magnitude of preoperative root-mean-square higher-order aberrations is greater than 0.35 μm. Wavefront-optimized aspheric corneal ablations attempt to avoid reducing the prolate eccentricity of the average cornea, and optimized treatments have shown improved visual outcomes compared with conventional LASIK treatments. A thorough knowledge of refractive surgery is important for any treating eye care practitioner to provide patients with the full range of options to correct all types of refractive errors., (Copyright © 2011 American Optometric Association. Published by Elsevier Inc. All rights reserved.)

Background: This study investigated the influence of corneal astigmatism, corneal curvature and meridional differences on corneal hysteresis (CH) and the corneal resistance factor (CRF) in a group of normal Chinese persons., Methods: Ninety-five participants were recruited and data from the eye with higher corneal astigmatism were analysed. The anterior corneal curvature was measured by corneal topography. The Goldmann-correlated intraocular pressure (IOPg), corneal-compensated intraocular pressure (IOPcc), CH and CRF at different meridians (default horizontal position, 10°, 20° and 30° along the superotemporal and inferonasal meridians) were obtained from an ocular response analyser. The corneal powers at these specific meridians also were calculated., Results: At the default position, the IOPg and CRF had weak correlations with corneal astigmatism, while the IOPcc and CH were not significantly correlated with corneal astigmatism. Both the IOPg and IOPcc were measured significantly higher at the default position. The CH and CRF were lower at the default position but the difference in the CRF from obliquity could not reach statistical significance. The CH was not significantly correlated with the corneal power at all meridians. The CRF correlated with the corneal power only at 30° superotemporal., Conclusion: Corneal astigmatism and head tilt did not have much effect on the measurement of CH and the CRF, both of which were lowest along the horizontal meridian. Clinically, the difference was small. The influence of corneal power on CH and the CRF was minimal., (© 2011 The Authors. Clinical and Experimental Optometry © 2011 Optometrists Association Australia.)

Purpose: To investigate the effects of cyclopentolate hydrochloride 1% on the main numerical parameters of anterior segment with Pentacam rotating Scheimpflug camera in children., Setting: Ege University Faculty of Medicine, Department of Ophthalmology., Methods: Pentacam measurements of 50 (23 boys and 27 girls) children before and after 45 min of cyclopentolate hydrochloride 1% instillation were performed and compared with 31 (17 boys and 14 girls) no medication instilled control group. Measurements of the control group (cycloplegia-free) were taken at two separate sessions with 45-min intervals. For comparison of the test parameters, paired t-test in the groups and unpaired t-test in between the groups were used., Results: Mean ages in the study and control groups were 10.06 ± 2.87 (range 6 and 16 years) and 9.87 ± 2.72 (range 6 and 16 years), respectively, and the difference was statistically insignificant (p > 0.05). In the study group, measurements between two sessions were significantly different for the parameters of anterior chamber depth (ACD), anterior chamber volume (ACV) and central corneal thickness (CCT) (p < 0.05), whereas none of the parameters was different between two sessions for control group., Conclusions: Cyclopentolate hydrochloride 1% instillation leads to significant decrement in CCT. ACD and ACV are the other important refractive parameters that increase significantly after cycloplegia. Effects of cycloplegia on these parameters for Pentacam measurements should be regarded for proper clinical interpretation in children., (© 2011 The Authors. Acta Ophthalmologica © 2011 Acta Ophthalmologica Scandinavica Foundation.)

To evaluate the topographic changes of cornea after pars plana vitrectomy (PPV) with the 23-gauge- (23-G) transconjunctival sutureless vitrectomy (TSV) system within the first postoperative month. In this prospective study, corneal topographic changes were evaluated in 24 eyes of 24 patients who underwent PPV with the 23-G TSV system. All eyes underwent computer-assisted videokeratography using NAVIS (Nidek Advanced Vision Information System) software preoperatively and at the first day, first week, and first month postoperatively. The topographic parameters that were analyzed statistically were the average corneal power (ACP), corneal surface cylinder (CSC), surface asymmetry index (SAI), and surface regularity index (SRI). Mean induced astigmatism was estimated by vector analysis software. The Wilcoxon test was used for statistical analysis. Mean ACP was 43.12±1.16 diopters (D) preoperatively and 42.88±1.44 D at first day (P=0.301), 43.04±1.14 D at first week (P=0.796), and 43.32±1.17 D at first month postoperatively (P=0.187). Mean CSC was 0.61±0.32 D preoperatively and 0.71±0.48 D at first day (P=0.918), 0.60±0.25 D at first week (P=0.826), and 0.70±0.33 D at first month postoperatively (P=0.414). Mean SAI was 0.12±0.05 preoperatively and 0.21±0.16 at first day (P=0.070), 0.15±0.06 at first week (P=0.176), and 0.16±0.09 at first month postoperatively (P=0.198). Mean SRI was 0.41±0.37 preoperatively and 1.05±0.41 at first day (P=0.001), 0.54±0.42 at first week (P=0.211), and 0.41±0.5 at first month postoperatively (P=0.861). Mean surgically induced astigmatism was 0.67±0.7 D at first day, 0.36±0.2 D at first week, and 0.33±0.17 D at first month postoperatively. Corneal surface and astigmatic changes were observed to be insignificant in the early postoperative period after PPV with the 23-G TSV system.

Purpose: Hereditary hyperferritinemia cataract syndrome (HHCS), an autosomal-dominant disorder characterized by hyperferritinemia and bilateral cataracts, is caused by mutations in the iron-responsive element of the ferritin light chain (FTL) gene. The purpose of this study is to describe the genotypic and phenotypic manifestations of HHCS observed in 2 large sets of unrelated American families., Methods: Forty-five patients were recruited from 2 unrelated families. Each underwent ophthalmological and general physical evaluation as well as laboratory testing of serum ferritin, iron, transferrin saturation, and total iron binding capacity. Serum DNA was evaluated for mutations by DNA amplification and sequencing of the FTL gene., Results: Numerous cortical and nuclear white opacities in a stellate pattern occurred in 22 affected individuals and were the only clinical manifestation of HHCS. Of the 22, 16 (73%) demonstrated >1.00 D of astigmatism. Genetic analysis revealed mutation G32A in Pedigree 1 and mutation G32T in Pedigree 2, both heterozygous and located in the iron-responsive element of the ferritin light chain mRNA. Serum ferritin levels of affected subjects ranged from 555 to 2,453 μg/L (normal range, 24-336 μg/L male, 11-307 μg/L female), with greater ferritin levels and more severe cataracts associated with mutation G32A., Conclusions: Most clinical and genetic findings from these families are consistent with previous reports of HHCS. Astigmatism, previously not associated with HHCS, was present in the majority. Ferritin levels and age of cataract surgery varied among subjects with both FTL gene mutations, suggesting that phenotypic variability is modulated by other genetic or environmental factors., (Copyright © 2011. Published by Mosby, Inc.)

Purpose: To determine the spherical wave aberration of the human eye based on corneal topography., Methods: Based on the pre- and postoperative status of 146 consecutive eyes (median patient age 36 years), the correlations between spherical aberration and asphericity and between corneal and ocular spherical aberrations were determined using simple linear regression methods. The asphericity (Q) values for which spherical aberration equals zero as well as the reference Q values for which corneal spherical aberration equals ocular spherical aberration have been determined. Patients underwent LASIK using the AMARIS excimer laser platform (SCHWIND eye-tech-solutions). All ablations were based on aspheric aberration-neutral profiles., Results: Corneal and ocular spherical aberrations correlate well with Q value and the value p · R(-3) in patients before and after LASIK for myopic astigmatism. A Q value of -0.19 to -0.27 can provide zero ocular spherical aberration in patients before and after LASIK for myopic astigmatism. Ocular spherical aberration is induced at a rate of half the induced corneal spherical aberration. A reference Q value of -0.12 to +0.01 can provide corneal spherical aberration equal to ocular spherical aberration in patients before and after LASIK for myopic astigmatism., Conclusions: Ocular and corneal wave aberrations are two different concepts that are not interchangeable. As for spherical aberration, a simple static model with a reference cornea deviating from a Cartesian oval can provide a 2:1 correspondence between corneal and ocular spherical aberration., (Copyright 2011, SLACK Incorporated.)

Purpose: To examine the efficacy and safety of topography-based limbal relaxing incision (LRI) surgery., Methods: Forty-four eyes of 36 consecutive patients who underwent cataract surgery more than 1 month previously, had refractive against-the-rule astigmatism of ≥2.00 diopters (D), and were scheduled to undergo LRI surgery were enrolled in the study. Patients were randomized into two groups-a topography-based LRI group (19 eyes of 14 patients) and a conventional LRI group (25 eyes of 22 patients). The topography-based LRI procedure comprised 3 steps: placing a mark on the cornea and conjunctiva, identifying this mark in the topographic image, and performing LRI based on the location of the mark. In the conventional LRI group, the horizontal meridian was marked under a slit lamp and LRIs were made based on the position of the horizontal mark., Results: Corneal astigmatism in the topography-based LRI group before and 1 month after surgery was 2.03±0.92 D and 1.33±0.69 D, respectively (P=.014). Corneal astigmatism in the conventional LRI group before and 1 month after surgery was 2.36±0.77 D and 0.93±0.70 D, respectively (P<.0001). Fourier harmonic analysis of the topography data demonstrated that regular astigmatism was significantly decreased in the two groups. The mean regular astigmatism was not significantly different before and after LRI between groups, whereas the variances (mean of the deviation squared from its mean) of regular astigmatism were significantly different between groups 1 month after LRI., Conclusions: Compared with conventional LRI surgery, a topography-based procedure may reduce the deviation of the effect of LRIs., (Copyright 2011, SLACK Incorporated.)

Purpose: To describe the effect of the corneal asphericity and toricity on the map patterns and best fit sphere (BFS) characteristics in elevation topography., Methods: The corneal surface was modeled as a biconic surface of principal radii and asphericity values of r1 and r2 and Q1 and Q2, respectively. The apex of the biconic surface corresponded to the origin of a polar coordinates system. Minimization of the squared residuals was used to calculate the values of the radii of the BFSs and apex distance (A-values: z distance between the corneal apex and the BFS) of the modeled corneal surface for various configurations relating to commonly clinically measured values of apical radius, asphericity, and toricity., Results: Increased apical radius of curvature and increased prolateness (negative asphericity) led to an increase in BFS radius but had opposite effects on the A-value. Increased prolateness resulted in increased BFS radius and A-value. Increasing toricity did not alter these findings. Color-plot elevation maps of the modeled corneal surface showed complete ridge patterns when toricity was increased and showed incomplete ridge and island patterns when prolateness was increased., Conclusions: High A-values in patients with corneal astigmatism may result from steep apical curvature and/or high prolateness (negative asphericity). The BFS radius may help in distinguishing between these 2 causes of increased A-values. Increased prolateness and decreased apical radius of curvature (often seen in keratoconus) have opposite effects on the BFS radius but similar effects on the apex distance.

Purpose: To evaluate the relationships between keratometry and collagen fibrillar structure of cornea by circular polarization biomicroscopy., Methods: Thirty-four subjects (63 eyes) were included in this study. Intraocular pressure (IOP) was measured, and keratometry was done with an automated keratometer. When the corneal astigmatism was larger than 0.75 diopter, corneal topography was done. After pupil dilation, the examiner placed a circular polarizing filter in front of the subject's eye. The images were captured by a camera connected to the slit lamp. Interfocal distance and angle were measured with ImageJ. The correlations between corneal astigmatism and interfocal distance-angle were examined by double angle vector diagram. Scalar analyses were done for the correlations between subject age and interfocal distance, between IOP and interfocal distance, and between mean cornea power and interfocal distance., Results: The mean age of the 34 subjects was 59 ± 16 years. Mean interfocal distances and angles determined by double angle vector diagram were 4.67 mm and -20.5 degrees in the right eye and 3.73 mm and +24.2 degrees in the left eye. The correlation between age and interfocal distance and between IOP and interfocal distance were statistically insignificant (P = 0.913 and 0.361, respectively). The interfocal distance and angle showed no statistically significant correlation with corneal astigmatism by vector analysis (P = 0.221 and 0.850, respectively). The fibrillar structure pattern in circular polarizing biomicroscopy showed no statistically significant relationship with the bow tie pattern in corneal topography (P = 0.762). However, analysis of the correlation between mean corneal power and interfocal distance showed a statistically significant, but weak positive correlation (r = 0.326, P = 0.019)., Conclusions: Interfocal distance determined through circular polarizing biomicroscopy showed a positive correlation with mean corneal power. But age, IOP, and corneal astigmatism did not show a significant correlation with interfocal distance and angle.

Background and Objective: To compare functional and morphological outcomes of 1.8-mm versus 2.2-mm microincision coaxial cataract surgery (MCCS)., Patients and Methods: Thirty eyes of 30 patients that underwent MCCS were randomized to two groups: 1.8-mm MCCS (group 1: 15 eyes) and 2.2-mm MCCS (group 2: 15 eyes)., Results: There were no significant between-group differences in uncorrected visual acuity, best-corrected visual acuity, keratometric astigmatism, and endothelial cell count. One day postoperatively, a greater increase of corneal thickness at the incision site was observed in group 1 compared to group 2 using anterior segment optical coherence tomography with no significant differences in tunnel morphometric features and confocal microscopy showed more tunnel edema in group 1 versus group 2 that resolved in both groups., Conclusion: Both 1.8- and 2.2-mm torsional MCCS were safe and efficient with easy surgical maneuvers and excellent functional and morphological results; 1.8-mm MCCS induced slightly greater tunnel edema shortly after surgery that resolved in the medium term., (Copyright 2011, SLACK Incorporated.)

Background: Tilted disc syndrome (TDS) is associated with characteristic ocular findings. The purpose of this study was to evaluate the ocular, refractive, and biometric characteristics in patients with TDS., Methods: This case-control study included 41 eyes of 25 patients who had established TDS and 40 eyes of 20 healthy control subjects. All participants underwent a complete ocular examination, including refraction and analysis using Fourier transformation, slit lamp biomicroscopy, pachymetry, keratometry, and ocular biometry. Corneal topography examinations were performed in the syndrome group only., Results: There were no significant differences in spherical equivalent (P = 0.13) and total astigmatism (P = 0.37) between groups. However, mean best spectacle-corrected visual acuity (Log Mar) was significantly worse in TDS patients (P = 0.003). The lenticular astigmatism was greater in the syndrome group, whereas the corneal component was greater in controls (P = 0.059 and P = 0.028, respectively). The measured biometric features were the same in both groups, except for the lens thickness and lens-axial length factor, which were greater in the TDS group (P = 0.007 and P = 0.055, respectively)., Conclusions: Clinically significant lenticular astigmatism, more oblique corneal astigmatism, and thicker lenses were characteristic findings in patients with TDS., (Copyright © 2010 American Optometric Association. Published by Elsevier Inc. All rights reserved.)

Purpose: To define the ocular parameters associated with anisometropic ambylopia in children with severe hyperopia, myopia, or astigmatism in 1 eye., Methods: Anisometropic and fellow eyes of 13 children, ages 7-8, with anisometropia >3.0 D and amblyopia without strabismus or other visually significant ocular pathology were studied. Axial length, corneal curvature, anterior chamber depth, and corneal diameter measurements of amblyopic and fellow eyes were obtained using the IOL Master (Carl Zeiss Meditec, Dublin, CA)., Results: Comparing amblyopic eyes with unaffected fellow eyes as reference, patients with anisohyperopia had shorter axial lengths by an average of 1.49 mm (p = 0.001), and patients with anisomyopia had longer axial lengths by an average of 2.26 mm. Corneal astigmatism was the source of amblyogenic refractive error in 1 child., Conclusions: In children with anisometropic amblyopia, interocular differences in spherical refractive error was attributed to axial length with no differences in corneal curvature, whereas the anisoastigmatism observed in 1 case was attributed to asymmetric corneal curvature., (Copyright © 2010 American Association for Pediatric Ophthalmology and Strabismus. Published by Mosby, Inc. All rights reserved.)

Wave aberrations of isolated ex vivo porcine crystalline lenses were measured by using a point-diffraction interferometer. This method allowed us to gain greater insight into the detailed aberration structure of eye lenses showing systematic presence of some dominant aberrations. In order of significance, astigmatism together with spherical aberration, coma, and trefoil are the main aberrations present in all lenses. We found a high correlation between the axis of both astigmatism and trefoil with the Y-shaped suture planes of the lens, revealing a subtle relationship between the induced aberrations and the histological features.