Search

PURPOSE: To evaluate peripheral refraction and contrast detection sensitivity in pseudophakic patients implanted with a new type of inverted meniscus intraocular lens (IOL) (Art25; Voptica SL) that was designed to provide better peripheral optics. METHODS: One month after cataract surgery, in 87 eyes implanted with the Art25 IOL, peripheral contrast detection sensitivity was measured psychophysically at 40° visual angle, both horizontally and vertically, and compared with a control group of 51 eyes implanted with standard biconvex IOLs. Thirty-one eyes with the Art25 IOL and 28 eyes from the control group were randomly selected to also measure peripheral refraction using a scanning Hartmann-Shack wavefront sensor along 80° in the horizontal meridian. RESULTS: Most patients achieved emmetropia and good visual acuity, and no significant adverse events were observed after cataract surgery with Art25 IOLs. Peripheral contrast detection sensitivity was significantly better ( P < .01) in the group with the Art25 IOL in both directions (7.78 ± 3.24 vs 5.74 ± 2.60 vertical, 10.98 ± 5.09 vs 7.47 ± 3.96 horizontal), which was in agreement with the optical quality improvement in the periphery due to a reduction of defocus (1.97 and 1.21 diopters [D] at 40° temporal and nasal sides) and astigmatism (1.17 and 0.37 D at 40° temporal and nasal sides) that was statistically significant ( P < .01) from 20° of eccentricity. CONCLUSIONS: Patients implanted with a new inverted meniscus IOL present a reduced amount of peripheral defocus and astigmatism compared to patients implanted with standard biconvex IOLs. This improvement in optical quality leads to better contrast detection sensitivity measured at 40° of eccentricity. [ J Refract Surg . 2022;38(4):229–234.]

A novel double-pass instrument and its data analysis method for the measurement of central and peripheral refraction is presented and validated in a group of healthy subjects. The instrument acquires in-vivo, non-cycloplegic, double-pass, through-focus images of the eye’s central and peripheral point-spread function (PSF) using an infrared laser source, a tunable lens and a CMOS camera. The through-focus images were analyzed to determine defocus and astigmatism at 0° and 30° visual field. These values were compared to those obtained with a lab-based Hartmann-Shack wavefront sensor. The two instruments provided data showing good correlation at both eccentricities, particularly in the estimation of defocus.

Current intraocular lenses (IOLs) are designed to substitute the cataractous crystalline lens, optimizing focus at the fovea. However, the common biconvex design overlooks off-axis performance, leading to a reduced optical quality in the periphery of the retina in pseudophakic patients compared to the normal phakic eye. In this work, we designed an IOL to provide better peripheral optical quality, closer in that respect to the natural lens, using ray-tracing simulations in eye models. The resulting design was a concave-convex inverted meniscus IOL with aspheric surfaces. The curvature radius of the posterior surface was smaller than that of the anterior surface by a factor that depended on the IOL power. The lenses were manufactured and evaluated in a custom-built artificial eye. Images of a point source and of extended targets were directly recorded at various field angles with both standard and the new IOLs. This type of IOL produces superior image quality in the whole visual field, being a better surrogate for the crystalline lens than the commonly used thin biconvex intraocular lenses.

We report a case of a patient that was implanted with an intracapsular ring during phacoemulsification cataract surgery. Namely, we report on refraction, posterior capsule transparency and IOL ACD and document photographically the appearance of the posterior capsule. It is suggested that the presence of the intracapsular ring has inhibited epithelial cell migration and prevented the formation of posterior capsule opacification (PCO) in the postoperative interval of 7 months. A comparison with the fellow eye of the same patient is made.

A handheld, standalone optical instrument was developed for the in-vivo assessment of the eye’s macular pigment optical density. The instrument is based on the reflectometry method, where the retina is illuminated with light of the appropriate spatial, temporal, and spectral characteristics and the reflected light from the fundus is collected using a high-speed photodetector. The collected light is then analysed and the corresponding value for macular pigment in the eye is computed.

Peripheral refraction is a relevant information in different areas of clinical optics, such as myopia or cataracts. We have developed and validated an optical instrument and a corresponding method for the in-vivo assessment of peripheral defocus and astigmatism from the recording of through-focus double-pass images.

Purpose:To investigate in vitro the accuracy of dynamic contour tonometry, Goldmann applanation tonometry, and Tono-Pen XL in edematous corneas.Methods:Experimental study included 20 freshly enucleated porcine eyes. Epithelium was debrided, and eyes were divided in four groups. Groups were immersed in 35%, 40%, 50%, and 60% glycerin solutions for 3 hours. Subsequently, globes were mounted in a special holder, and their intraocular pressure was hydrostatically adjusted. Intraocular pressure was measured by means of dynamic contour tonometry, Goldmann applanation tonometry, and Tono-Pen XL while adjusting true intraocular pressure to 17, 33, and 50 mm Hg. Ultrasound pachymetry was performed.Results:Mean corneal thickness was 914.5 ± 33.3 μm (730–1015 μm). In true intraocular pressure of 33 mm Hg, Goldmann applanation tonometry and dynamic contour tonometry significantly underestimated true intraocular pressure (mean Goldmann applanation tonometry: 14.7 ± 4.8 mm Hg, p Conclusion:Goldmann applanation tonometry, dynamic contour tonometry, and Tono-Pen XL underestimate intraocular pressure when measured under edematous conditions. Tono-Pen XL showed better accuracy, especially in lower true intraocular pressure. The measurement error increases when true intraocular pressure increases in all three methods.

Purpose To show the importance of measuring the angular distribution of straylight as an in vitro test for intraocular lenses (IOLs). Methods The optical integration method was implemented to measure the point spread function, up to 5.1°, of IOLs immersed in a wet cell. The straylight parameter was calculated as the product of the point spread function by the squared angle. The effect of the scattered light is shown in extended images of a target surrounded by headlamps as glare sources. Three different IOLs were tested: (1) AcrySof IQ SN60WF, monofocal, (2) AcrySof IQ PanOptix, trifocal, and (3) Tecnis Symfony ZRX00, bifocal with extended depth of focus. Measurements were compared to previously reported clinical studies where the same IOL models were implanted. Results The mean amount of scattered light, between 1.0° and 5.1°, generated by each IOLs were, in deg2sr- 1 units: (1) 1.2, (2) 12.1, and (3) 33.4. Lens (3) present a high amount of straylight related to a halo of an approximate diameter of 2°. Conclusions In vitro measurements of the angular distribution of the point spread function of different types of IOLs showed important aspects related to their manufacturing quality. These results are in line with previous clinical findings where glare sensitivity was tested in the same angular range. Translational relevance In vitro measurement of angular dependence of straylight in IOLs, regardless their design, provides a valuable feedback to improve their optical quality. The minimization of the amounts of straylight positively impacts the recurrence of photic phenomena.

PURPOSE: Scattering in the eye occurs mainly at two sites: the eye's optical media and the deeper retinal layers. Although the two phenomena are often treated collectively, their spatial domain of contribution to the double-pass Point Spread Function (PSF) is different: the fundus effect is limited to the narrow and middle part of the PSF whereas scattering in the eye's optics extends also to wide angles. The objective of this work was to determine the domain of contribution at the double-pass PSF of light scattered in the ocular media and the ocular fundus, using simulated and experimental data for two different wavelengths and for two different pigmentations. METHODS: Diffuse reflection was simulated using Monte Carlo simulations for a four-layer retinal fundus model. Four situations were simulated in total for two different choroidal absorptions at two different wavelengths. Light diffusion in the fundus was the only phenomenon considered in the model. The simulations were compared against experimental fundus reflection data obtained in a previous study. RESULTS: The simulations showed that at 560 nm, diffusion in the fundus causes light to extend to a radius of 2°, independently of the choroidal pigmentation, whereas at 650 nm it extends to radii of 4.5° and 4° for low and high choroidal pigmentation respectively. Experimental data showed a similar behaviour at low angles where light diffusion in the fundus is dominant, but different at higher angles due to scattering in the ocular media. CONCLUSION: The spatial contribution of light diffused in the ocular fundus to the PSF was found to be limited to narrower angles compared to that of scattering at the ocular media. The comparison of simulated and optical data showed that beyond 2° at 560 nm and 4–4.5° at 650 nm the only phenomenon contributing to the PSF is scattering in the ocular media, whereas the fundus contribution can be assumed as negligible.

Purpose Straylight refers to an optical phenomenon that takes places in the eye and leads to a deterioration of the retinal image. Past clinical findings suggest an increase of straylight with the eye's axial length, but the aetiology of the phenomenon was unclear. The purpose of this work is to demonstrate, through raytracing, simple geometrical optics, and the well-established inverse-angle square law for the angular distribution of straylight, why straylight increases when a myopic eye is corrected with spectacles. Methods The angular dependence of straylight is investigated using geometrical optics. An expression relating the eye's 2(nd) nodal point, the ocular axial length and the eye's straylight parameter S is found. Subsequently, using a model of the human eye, the location of the 2(nd) nodal point is computed using ray tracing for different axial lengths and refractive corrections. Finally, the results are compared against psychophysical data for the straylight parameter, corrected for the subject's age. Results When correcting axial myopia using spectacles, the eye's 2(nd) nodal point shifts towards the retina and away from the scattering plane, leading to an increase in straylight. Meanwhile, straylight should theoretically decrease in hyperopic eyes. Contact lenses keep the 2(nd) nodal point relative stable, leading to a very minor change in straylight with axial length. Our model has shown good agreement with previously taken straylight measurements in real eyes, explaining the observed change of straylight with ocular axial length. Conclusion We proposed an explanation for the underlying optical mechanism for the clinically observed increase of straylight with axial myopia, when corrected with glasses. Our model predicts that the increase can be as high as 0.12 log units for a myopic eye with 10 dioptres, which agrees with prior observations.

Macular pigment is a yellowish pigment of purely dietary origin, which is thought to have a protective role in the retina. Recently, it was linked to age-related macular degeneration and improved visual function. In this work, we present a method and a corresponding optical instrument for the rapid measurement of its optical density. The method is based on fundus reflectometry and features a photodetector for the measurement of reflectance at different wavelengths and retinal locations. The method has been tested against a commercially available instrument on a group of healthy volunteers and has shown good correlation. The proposed instrument can serve as a rapid, non-midriatic, low-cost tool for the measurement of macular pigment optical density.

Harvey S Uy,1,2 Carolina Tesone-Coelho,3 Harilaos Ginis4 1Peregrine Eye and Laser Institute, Makati, Philippines; 2Department of Ophthalmology and Visual Sciences, University of the Philippines, Manila, Philippines; 3Department of Research and Development, InfiniteVision Optics, Strasbourg, France; 4Research Department, Athens Eye Hospital, Athens, Greece Purpose: Eyes that have undergone phacoemulsification with implantation of a multicomponent intraocular lens (MCIOL) may further undergo an enhancement procedure for correction of residual refractive errors. The enhancement procedure is accomplished by exchanging the front lens used in the primary surgery with another lens containing the correct dioptric power. We evaluated the efficacy and safety of enhancement procedures among eyes that received an MCIOL.Methods: A total of 25 eyes that had undergone phacoemulsification with implantation of an MCIOL were found to have a residual error of refraction (spherical equivalent ≥0.75 D) 3 months after primary cataract surgery, and underwent further enhancement surgery. The main study outcomes were uncorrected and corrected distance visual acuity, subjective refraction, anterior-chamber depth, pachymetry, and endothelial cell count.Results: There was a statistically significant improvement in uncorrected distance visual acuity of approximately two lines after enhancement surgery (0.20±0.20–0.02±0.08 logMAR, P

The purpose of this work was to evaluate peripheral image quality in the pseudophakic eye using computational, physical, and psychophysical methods. We designed and constructed a physical model of the pseudophakic human eye with realistic dimensions using a corneal phantom and a board-only camera that was pivoted around an axis that matched the anatomical center of a human retina, assuming a radius of curvature of 12 mm, while it was submersed in a 23.4 mm long water filled chamber to emulate human ocular axial length. We used this optical setup to perform direct recording of the point spread function (PSF) and the associated retinal images for a commercial intraocular lens (IOL). Additionally, psychophysical tests were carried out to investigate the impact of the off-axis astigmatism in peripheral visual performance, where spectacle-induced astigmatism simulated the pseudophakic conditions in healthy subjects. Our findings using the physical eye model confirm the existence of large amounts of astigmatism in the periphery of the pseudophakic eye. The psychophysical tests revealed a significant reduction of detection sensitivity in the peripheral visual field. The latter suggests that off-axis astigmatism in patients implanted with IOLs may have performance and safety implications for activities requiring efficient peripheral vision.

Fundus reflectometry is a common in-vivo, noninvasive method to estimate the macular pigment optical density (MPOD). The measured density, however, can be affected by the individual’s intraocular scattering. Scattering causes a reduction in the contrast of the fundus image, which in turn leads to an underestimation of the measured density. Intraocular scattering was measured optically in a group of seven young, healthy subjects using the method of optical integration and was subsequently used to correctly estimate the MPOD from fundus images. It was shown that when scattering is not considered, the measured optical density using fundus reflectometry can be underestimated by as high as 16% for our group of subjects.

Purpose.To compare ocular rigidity (OR) and outflow facility (C) in patients with nonproliferative diabetic retinopathy (NPDR) and control subjects.Methods. Twenty-four patients with NPDR (NPDR group) and 24 controls (control group) undergoing cataract surgery were enrolled. NPDR group was further divided into patients with mild NPDR (NPDR1-group) and patients with moderate and/or severe NPDR (NPDR2-group). After cannulation of the anterior chamber, a computer-controlled device was used to infuse saline and increase the intraocular pressure (IOP) in a stepping procedure from 15 to 40 mmHg. Ocular rigidity and outflow facility coefficients were estimated from IOP and volume recordings.Results. Ocular rigidity was 0.0205 μL−1in NPDR group and 0.0202 μL−1in control group (P=0.942). In NPDR1-group, OR was 0.017 μL−1and in NPDR2-group it was 0.025μL−1(P=0.192). Outflow facility was 0.120 μL/min/mmHg in NPDR-group compared to 0.153 μL/min/mmHg in the control group at an IOP of 35 mmHg (P=0.151). There was no difference in C between NPDR1-group and NPDR2-group (P=0.709).Conclusions. No statistically significant differences in ocular rigidity and outflow facility could be documented between diabetic patients and controls. No difference in OR and C was detected between mild NPDR and severe NPDR.

When setting off on a journey of discovery it often helps to have a sense of direction, a particular goal or a coveted treasure that makes all the hardships on the way to get there worthwhile. In science these treasures often come in the form of understanding, built up one tiny gold piece of insight at a time. But unlike the stories of Tolkien, the protagonists of a scientific journey cannot just set out blindly towards a vaguely‐described goal without bothering about things such as finances. Instead, each step along the way must be considered carefully before it hits the ground, while thinking ahead two or three paces, as resources are scarce and funding agencies insist each step should have a reasonable chance of success. Each step may also turn out to be in the wrong direction, or, if you are very lucky, a leap straight for the gold. Consequently these journeys are often slow, with people dedicating an entire PhD to a single step. One can imagine that under these circumstances individual travellers may lose sight of the final goal ahead. But, luckily, in science we do not walk the entire journey by ourselves. As Bernard of Chartres and Isaac Newton both suggested, we are carried on the shoulders of our forebears until it is time to make our own steps, in the hope one of us will eventually reach the treasure of understanding. In that context it is good to stop sometimes and to look at the scenery of where we are now and all the places we may go.

Introduction: A previous study has employed shear-wave ultrasound elastographic imaging to assess corneal rigidity in an ex-vivo porcine eye model. This study employs the same modality in vivo in a rabbit eye model in order to assess lens, ciliary body and total ocular rigidity changes following the instillation of atropine and pilocarpine. Methods: Ten non-pigmented female rabbits were examined. Measurements of the lens, ciliary body and total ocular rigidity as well as lens thickness and anterior chamber depth were taken with the Aixplorer system (SuperSonic Imagine, Aix-en-Provence, France) with the SuperLinear™ SL 15-4 transducer in both eyes at baseline as well as after pilocarpine and atropine instillation. The IOP was also measured with the TonoPen tonometer. Results: Changes in rigidity in the examined areas following atropine instillation were statistically not significant. Ciliary body rigidity was significantly increased whereas lens and total ocular rigidity were significantly reduced following pilocarpine instillation. The decrease in lens rigidity following pilocarpine was significantly associated with the respective increase in ciliary body rigidity. Conclusions: Shear-wave ultrasound elastography can detect in vivo rigidity changes in the anterior segment of the rabbit eye model and may potentially be applied in human eyes, providing useful clinical information on conditions in which rigidity changes play an important role, such as glaucoma, pseudoexfoliation syndrome or presbyopia.

Increased intraocular scatter degrades quality of vision, especially in the presence of glare sources. Standard tests, such as visual acuity, are not well suited to capture this condition. There are specific methods to measure intraocular scatter, but require dedicated instruments. In this work, we propose a method to estimate the amount of scatter by combining to sequential measurements of the contrast sensitivity function for two conditions, with and without a glare source. We applied the approach in a group of young subjects with no know ocular pathology fitted with photographic diffusing filters. The straylight estimates were compared with those provided by two alternative techniques, one based on the compensation comparison method and the other the optical integration. The results obtained with the three approaches were in a good agreement, demonstrating the feasibility of the proposed method.

The 9th European Meeting on Visual Physiological Optics (VPO2018) was held August 29-31, 2018, in Athens, Greece. This issue of the Journal of the Optical Society of America A (JOSA A) is a dedicated feature, including numerous articles that span a large range of visual optics related topics, ranging from geometrical optics to visual psychophysics and from optical metrology to ophthalmic diagnostic technologies. The next VPO meeting will be held August 2020 in Cambridge, UK.

Ioannis G Pallikaris, Nela R Stojanovic, Harilaos S Ginis Institute of Vision and Optics, Department of Medicine, University of Crete, Heraklion, Crete, Greece Purpose: The aim of this study is to demonstrate the functionality of a new design of a thick endocapsular open ring for prevention of anterior capsule opacification (ACO) and posterior capsule opacification (PCO). Setting: The Institute of Vision and Optics, University of Crete and University Hospital of Heraklion, Crete, Greece. Design: Prospective, interventional pilot study. Methods: Fifteen patients (17 eyes) underwent cataract surgery with phacoemulsification. During surgery, a thick endocapsular open ring (peripheral capsule reconstructor) was inserted into the capsular bag, prior to intraocular lens (IOL) implantation. Six different models of IOL were implanted. Postoperatively, the degree of ACO and PCO was evaluated and described as none, mild, moderate, or severe. Results: The mean follow-up period was 30±8.06 months (range: 12–36 months). At the last follow-up, mild PCO was observed in only three eyes and mild ACO in three patients. The centration of IOLs was good in all but one eye, which had a tilted IOL. Conclusion: The results of this pilot study suggest that the implantation of a new design of thick endocapsular open ring is feasible and may contribute to the prevention of PCO and ACO after cataract surgery. Keywords: intraocular implant, cataract, phacoemulsification, silicone

A novel mathematical and physical method of generating complete ocular wavefronts, based on the parametrization and numerical optimization of the discrete cosine spectrum of the phase maps.

Light scattering in the eye affects the quality of vision and its effect increases with aging and related pathologies, such as cataracts. Simulating methods were developed in order to reproduce the effects of this phenomenon. We introduce a statistical model of wavefront perturbations at the pupil plane of the eye that replicates the characteristic angular distribution of the light distribution over the retina. Our approach is based on the parameterization of the discrete cosine spectrum of the wavefront perturbation. The model performance was experimentally validated with a dedicated setup using a liquid crystal on silicon device as a spatial phase modulator. This instrument can be used for further visual experiments with controlled induction of light scattering.

Purpose. Corneal haze is a well-known pathology associated with decreased corneal transparency and increased ocular scattering. Clinically, haze is typically estimated as the amount of backscattered light observed in a slit lamp examination while the small angle forward scattering cannot be directly observed. It was the purpose of this study to demonstrate a single-pass technique to objectively measure forward scattering properties of excised rabbit corneas. Methods. Six rabbits (twelve eyes) were used in this study. All eyes underwent photorefractive keratectomy for 4Di n a 6 mm ablation zone. Seven weeks later, the rabbits were examined under general anesthesia. All eyes expressed mild to severe haze. A purposely-developed single pass optical setup was used both to estimate the angular distribution and fraction of forward light scattering in excised rabbit corneas. Moreover, subjective clinical corneal haze evaluation was performed as well as corneal confocal microscopy of all corneas. Finally, the corneas were histopathologically examined. Results. Light scattering in the rabbit corneas followed a narrow forward peaked distribution. A new parameter, Ballistic Ratio, was introduced to represent a parameter for absolute quantification of forward light scatter, corresponding to the power ratio of the radiation that is not scattered by each sample. A negative correlation between clinically subjective corneal haze and forward scatter (Pearson’s Coefficient 0.23) was found, which suggests the relation between increased forward and backward scatter. Activated myofibroblasts, collagen irregularities and vacuoles present in a sub-epithelial layer over the treated area of the cornea had characteristic dimensions in accordance to the measured scatter distribution. Conclusions. Corneal light scatter associated with the increased amount of haze after excimer laser ablation has a narrowly forward distribution that can be attributed to the subepithelial structures observed in treated corneas. (Optom Vis Sci 2008;85:843–848)

Purpose. To describe a new software tool for the detailed presentation of corneal topography measurements variability by means of color-coded maps. Methods. Software was developed in Visual Basic to analyze and process a series of 10 consecutive measurements obtained by a topographic system on calibration spheres, and individuals with emmetropic, low, high, and irregular astigmatic corneas. Corneal surface was segmented into 1200 segments and the coefficient of variance of each segment’s keratometric dioptric power was used as the measure of variability. The results were presented graphically in color-coded maps (Variability Maps). Two topographic systems, the TechnoMed C-Scan and the TOMEY Topographic Modeling System (TMS-2N), were examined to demonstrate our method. Results. Graphic representation of coefficient of variance offered a detailed representation of examination variability both in calibration surfaces and human corneas. It was easy to recognize an increase in variability, as the irregularity of examination surfaces increased. In individuals with high and irregular astigmatism, a variability pattern correlated with the pattern of corneal topography: steeper corneal areas possessed higher variability values compared with flatter areas of the same cornea. Numerical data permitted direct comparisons and statistical analysis. Conclusions. We propose a method that permits a detailed evaluation of the variability of corneal topography measurements. The representation of the results both graphically and quantitatively improves interpretability and facilitates a spatial correlation of variability maps with original topography maps. Given the popularity of topography based custom refractive ablations of the cornea, it is possible that variability maps may assist clinicians in the evaluation of corneal topography maps of patients with very irregular corneas, before custom ablation procedures. (Optom Vis Sci 2007;84:E962–E968)

Purpose: A variety of anti-glaucomatous shunt designs have been proposed so far. This study evaluates the feasibility of a novel shunt design, the intra-scleral parathalamus implant (IPI), in a rabbit eye model. Methods: Ten healthy albino rabbits were included. Measurements of the IOP, using TonoPenXL, as well as ocular rigidity (OR) and aqueous outflow facility (AO), using a previously described methodology, were performed in both eyes of each animal. Subsequently, the IPI was implanted at the left eye of all animals whereas the right eye served as control. Measurements of IOP were repeated at weekly intervals for 2 months postoperatively whereas measurements of OR and AO were repeated at the 1st and 2nd postoperative week. Results: The IOP decreased significantly whereas the AO increased significantly postoperatively at the operated eyes. A significant postoperative decrease in OR was also recorded at the operated eyes. Respective differences at the fellow eyes were statistically not significant. Two animals developed postoperative complications and were excluded from follow-up. Conclusions: Results imply that the implantation of the IPI is feasible in rabbit eyes with significant favorable effects on the IOP, AO and OR.

Purpose The intraocular pressure (IOP) is determined by a dynamic equilibrium between the production and outflow of the aqueous humour. The relationship between IOP and the outflow rate through the conventional and unconventional pathway is quantified by the outflow facility coefficient (C). The purpose of this study is to employ a direct (manometric) tonographic technique and determine C as well as its inverse, resistance (R), as a function of IOP in the living human eye. Methods Nineteen cataract patients were enrolled in the study. An intraoperative manometric device was used to measure IOP. After cannulation of the anterior chamber, the IOP was increased by infusion of controlled amounts of saline solution. At 40 mmHg, the infusion stopped, and a pressure sensor recorded the IOP. The measured pressure–volume relationship was considered in order to convert pressure changes to corresponding ocular volume changes. An appropriate mathematical model was applied to calculate C and (its inverse), R. Results The average C was 0.0672 ± 0.0296 μl/min/mmHg at 40 mmHg and 0.2652 ± 0.1164 μl/min/mmHg at 20 mmHg. There was a strong dependence of coefficient C on IOP in all subjects (p

PURPOSE: The aim of the current study was to control the hypothetical effects of decreased laser energy delivered to the peripheral cornea during phototherapeutic keratectomy (PTK) and provide quantitative calculation of induced low and high order aberrations. METHODS: We employed a model eye to simulate the refractive effect of homogeneous laser corneal irradiation, as in PTK, for different laser fluences (range 125 to 225 mJ/cm2) and treatment depths up to 200 pm. RESULTS: The hyperopic shift induced by the relatively lower energy delivered at the peripheral ablation zone during PTK was proportional to the treatment depth and inversely proportional to the energy fluence. The hyperopic shift calculated using the above ablation parameters was lower compared to previously reported clinical results. Higher order wavefront aberration (total root mean square) changes were of minimal significance for treatment depths up to 200 urn. CONCLUSIONS: After PTK, a hyperopic shift cannot be attributed to the energy delivery method alone. Modification of laser energy delivery algorithms may only minimize PTK-induced hyperopia. [J Refract Surg 2003;19:443-448]

Optical measurement of straylight in the human eye is a challenging task. Issues such as illumination geometry, detector sensitivity and dynamic range as well as various inherent artifacts must be addressed. We developed a novel instrument based on the principle of double-pass optical integration adapted for fast measurements in a clinical setting. The experimental setup was validated using four different diffusers introduced in front of the eyes of ten subjects. Measurement limitations and future implications of rapid optical measurement of straylight in ophthalmic diagnosis are discussed.

The photoablatable lenticular modulator (PALM) technique is a method developed at the University of Crete for the correction of corneal surface irregularities. The PALM technique refers to corneal excimer laser phototherapeutic keratectomy through a gel used as a masking agent. The authors describe the basic principles of the PALM procedure as well as the refractive and visual outcome of selected cases with different types of corneal irregularities treated with this technique

BACKGROUND: Corneal hydration is an important factor in laser corneal ablation. In photorefractive keratectomy (PRK), corneal ablation rate and final ablation surface quality are strongly dependent on corneal hydration. We used, a spectroscopic technique for monitoring corneal hydration during PRK. METHODS: Hydroxyethylmethacrylate (HEMA) was employed for corneal hydration modeling. Hydrated HEMA samples were irradiated with a pulsed Nd:YAG laser (1064 run, 10 mJ/pulse, pulse duration 15 nsec). Successive emission spectra corresponding to different degrees of hydration were recorded on a gated optical multichannel analyzer. The weight of the sample and hence its water content was monitored during the entire procedure with a sensitive balance. One rabbit and one human cornea were used to demonstrate the spectral analogy between the model and corneal tissue. RESULTS: The most noticeable dependence on water content of the substrate was that of atomic emission lines of Ca at 393 nm and 396 nm. CONCLUSION: Plasma emission spectra exhibited significant dependence on sample hydration. This dependence can be used for estimation of water content of irradiated model material and real cornea. [J Refract Surg 1998;14:655-660]

PURPOSE: To present a case of phacoemulsification and implantation of an accommodating intraocular lens (IOL) in a patient with cataract formation after previous refractive surgery. METHODS: A 50-year-old man, who initially had photorefractive keratectomy to correct moderate myopia, developed a cataract in one eye. He subsequently underwent phacoemulsification and implantation of a ICU accommodating IOL, as he wished to remain spectacle independent. RESULTS: The patient's distance vision was fully restored. However, accommodative function, which was assessed using subjective and novice objective techniques, was only partially restored. CONCLUSIONS: Although the accommodating IOL fully restored the patient's distance vision, accommodative function was only partially restored. [J Refract Surg. 2006;22:106-108.]

To compare ocular rigidity (OR) and outflow facility (C) coefficients in medically treated open-angle glaucoma (OAG) patients and controls, and to investigate differences in ocular pulse amplitude (OPA) and pulsatile ocular blood flow (POBF) between the two groups.Twenty-one OAG patients and 21 controls undergoing cataract surgery were enrolled. Patients with early or moderate primary or pseudoexfoliative OAG participated in the glaucoma group. A computer-controlled system, consisting of a pressure transducer and a microstepping device was employed intraoperatively. After cannulation of the anterior chamber, IOP was increased by infusing the eye with microvolumes of saline solution. IOP was recorded after each infusion step. At an IOP of 40 mm Hg, an IOP decay curve was recorded for 4 minutes. OR coefficients, C, OPA, and POBF were estimated from IOP and volume recordings.There were no differences in age or axial length in the two groups. The OR coefficient was 0.0220 ± 0.0053 μl(-1) in the OAG and 0.0222 ± 0.0039 μl(-1) in the control group (P = 0.868). C was 0.092 ± 0.082 μL/min/mm Hg in the glaucoma group compared with 0.149 ± 0.085 μL/min/mm Hg in the control group at an IOP of 35 mm Hg (P0.001) and 0.178 ± 0.133 μL/min/mm Hg vs. 0.292 ± 0.166 μL/min/mm Hg, respectively, at an IOP of 25 mm Hg (P0.001). There were no differences in OPA or POBF between the two groups in baseline and increased levels of IOP (P0.05).Manometric data reveal lower C in OAG patients and increased C with increasing IOP. There were no differences in the OR coefficient, OPA, and POBF between medically treated OAG patients and controls, failing to provide evidence of altered scleral distensibility and choroidal blood flow in OAG.

Intraocular scattering affects fundus imaging in a similar way that affects vision; it causes a decrease in contrast which depends on both the intrinsic scattering of the eye but also on the dynamic range of the image. Consequently, in cases where the absolute intensity in the fundus image is important, scattering can lead to a wrong estimation. In this paper, a setup capable of acquiring fundus images and estimating objectively intraocular scattering was built, and the acquired images were then used for scattering compensation in fundus imaging. The method consists of two parts: first, reconstruct the individual’s wide-angle Point Spread Function (PSF) at a specific wavelength to be used within an enhancement algorithm on an acquired fundus image to compensate for scattering. As a proof of concept, a single pass measurement with a scatter filter was carried out first and the complete algorithm of the PSF reconstruction and the scattering compensation was applied. The advantage of the single pass test is that one can compare the reconstructed image with the original one and see the validity, thus testing the efficiency of the method. Following the test, the algorithm was applied in actual fundus images in human eyes and the effect on the contrast of the image before and after the compensation was compared. The comparison showed that depending on the wavelength, contrast can be reduced by 8.6% under certain conditions.

PURPOSE To study the relative impact of genetic and environmental factors on the variability of intraocular scattering within a classical twin study. METHODS A total of 64 twin pairs, 32 monozygotic (MZ) (mean age: 54.9 ± 6.3 years) and 32 dizygotic (DZ) (mean age: 56.4 ± 7.0 years), were measured after a complete ophthalmologic exam had been performed to exclude all ocular pathologies that increase intraocular scatter as cataracts. Intraocular scattering was evaluated by using two different techniques based on a straylight parameter log(S) estimation: a compact optical instrument based in the principle of optical integration and a psychophysical measurement. Intraclass correlation coefficients (ICC) were used as descriptive statistics of twin resemblance, and genetic models were fitted to estimate heritability. RESULTS No statistically significant difference was found for MZ and DZ groups for age (P = 0.203), best-corrected visual acuity (P = 0.626), cataract gradation (P = 0.701), sex (P = 0.941), optical log(S) (P = 0.386), or psychophysical log(S) (P = 0.568), with only a minor difference in equivalent sphere (P = 0.008). Intraclass correlation coefficients between siblings were similar for scatter parameters: 0.676 in MZ and 0.471 in DZ twins for optical log(S); 0.533 in MZ twins and 0.475 in DZ twins for psychophysical log(S). For equivalent sphere, ICCs were 0.767 in MZ and 0.228 in DZ twins. Conservative estimates of heritability for the measured scattering parameters were 0.39 and 0.20, respectively. CONCLUSIONS Correlations of intraocular scatter (straylight) parameters in the groups of identical and nonidentical twins were similar. Heritability estimates were of limited magnitude, suggesting that genetic and environmental factors determine the variance of ocular straylight in healthy middle-aged adults.

Corneal biomechanical properties are usually measured by strip extensiometry or inflation methods. We developed a two-dimensional (2D) flap extensiometry technique, combining the advantages of both methods, and applied it to measure the effect of UV-Riboflavin cross-linking (CXL). Corneal flaps (13 pig/8 rabbit) from the de-epithelialized anterior stroma (96 μm) were mounted on a custom chamber, consisting of a BK7 lens, a reflective retina, and two reservoirs (filled with Riboflavin and silicone oil). Stretching the corneal flap during five pressure increase/decrease cycles (0-30 mm Hg) changed the refractive power of the system, whose Zernike aberrations were monitored with a ray-tracing aberrometer. Porcine flaps were used to test the system. Rabbits were treated with CXL unilaterally in vivo following standard clinical procedures. Flaps were measured 1 month postoperatively. An analytical model allowed estimating Young's modulus from the change in surface (strain) and pressure (stress). Confocal microscopy examination was performed before, and at different times after CXL. Flap curvature changed with increased function of IOP in pig flaps (23.4 × 10 -3 D/mm Hg). In rabbit flaps curvature changed significantly less in 1 month post CXL (P = 0.026) than in untreated corneas [17.0 vs. 6.36 millidiopter (mD)/mm Hg]. Young's modulus was 2.29 megapascals (MPa) in porcine corneas, 1.98 MPa in untreated rabbit corneas, and 4.83 MPa in 1 month post CXL rabbit corneas. At the same time, highly reflective structures were observed in the rabbit midstroma after treatment. 2D flap extensiometry allows estimating corneal elasticity in vitro. The measurements are spatially resolved in depth, minimize the effects of corneal hydration, and preserve the integrity of the cornea. The method proved the efficacy of CXL in increasing corneal rigidity after 1 month in rabbits. © Association for Research in Vision and Ophthalmology, Supported by European Young Investigator Award Grant EURYI 05-102-ES, the Spanish Government Grants FIS2008-02065 and FIS2011-25637 (SM), and a Formacion de Personal Investigador (FPI) Predoctoral Fellowship (SK).

The purpose of this study is to evaluate in-vitro the immediate effect of corneal collagen cross-linking (CXL) on corneal hydration and stiffness. Forty-two corneal buttons from freshly enucleated porcine eyes were immersed in riboflavin 0.1% in dextran 20% dilution for 3 h in order for their hydration to reach equilibrium. Corneal buttons where divided into two groups; the first group was stored in dark conditions while the other group was irradiated with UV radiation (370 nm) for 30 min to simulate CXL according to the clinically applied protocol. After irradiation, all corneas were immersed in dextran 20% solution for 3 additional hours. Subsequently, each button underwent weighing, thickness measurement, and was mounted in a special device for the measurement of force versus deformation by compression. Finally, all corneal buttons were dehydrated for 48 h in a desiccating oven set at 62 °C and weighed again to obtain their dry mass. Hydration (%) of each button was calculated. Mean corneal hydration in the irradiated and the non-irradiated group of corneas was 69.8 and 72.2%, respectively (p

Purpose A photo-polymerisable hydrophilic material (PEG/Irg) has been previously evaluated in terms of biocompatibility and toxicity in a series of laboratory animals. It was the purpose of this study to evaluate the bio-mechanical effect of lamellar implants created from PEG/Irg in porcine cadaver eyes. Methods Twenty porcine corneas where removed along with a 3 mm corneoscleral rim, de-epithelialised and mounted on an artificial anterior chamber. The pressure was maintained at 22 mmHg hydrostatically. In each cornea, a circular lamellar pocket (7mm diameter) was created manually. Thirty microliters of PEG/Irg in liquid form were injected in each pocket. A rigid contact lens was pressed on top of the cornea and the excessive quantity of PEG/Irg was leaked out of the pocket. The cornea was then irradiated with UV light (390nm, 4mW/cm2) and the PEG/Irg underwent a polymerization and the associated phase transition to form a rigid film. Mechanical measurements were performed by means of a purposely-developed device featuring a stepping motor and a load cell. By keeping the pressure constant the role of corneal stiffness is isolated. The force as a function of indentation was recorded for each specimen before and after the in-situ creation of the PEG/Irg film. Results The mean slope of force versus indentation for the reinforced group was 166.72 (±74.14) and the mean slope for the non-reinforced group was 116.94 (±21.16). The two-tailed P value equals 0.0033, equally meaning that the difference between those two groups was statistically different. Conclusion According to the results, there was a significant biomechanical reinforcement of the cornea following the in-situ creation of the polymer film.

Purpose To develop and demonstrate a new optical technique for the measurement of light scatter in the human eye based on extended source imaging in a double pass configuration. Methods The experimental setup is based on a double-pass (DP) configuration. Series of disks of uniform radiance having angular dimensions ranging from 0 to 9.1 degrees (radius) are projected on to the eye's retina and DP images are recorded by a cooled electron-multiplied CCD camera. Two spatially separated sub-apertures at the pupil are used for stimulus projection and imaging to minimise back-scatter and reflections. The derivative of the intensity of each recorded disk with respect to disk radius (in angular units) was fitted to a mathematical model of the wide-angle double pass point-spread function (PSF) and from that the underlying single-pass PSF was computed. The setup was first validated using artificial eyes with known scattering properties and used in a group of normal human eyes. Results The derivative of central disk intensity with respect to disk radius was measurable up to the complete range of the angular dimensions of the projected disks (9.1 degrees of visual field). Different features can be obtained from the estimated PSF to characterize not only the amount of scatter but also its angular dependence. Conclusion A new optical method to measure scatter in the eye was developed and demonstrated. The procedure is sensitive enough to consistently detect differences in the light scatter intensity between normal healthy eyes and can be a significant step towards the complete optical characterization of the eye.

Purpose Several instruments and methods are applied for the non invasive measurement of intraocular pressure, ocular rigidity and pulsatily blood flow. Most of this instruments and methods are based on the deformation force-area principle. The purpose of this study was to present a novel device for the measurement of intraocular pressure, ocular rigidity and pulsatily blood flow. Methods The device consists of an opto-mechanical head comprising a deformation sensor and a force sensor, a camera and a microstepping motor. The deformation sensor is an optoelectronic device consisting of two beamsplitters a plano-convex lens, an illuminating fiber and a receiving fiber. Eighty three eyes were enrolled in a preliminary study, the intraocular pressure was measured with the novel device followed by a Goldman applanation tonometer measurement. Results The average IOP measured by the device was 17 (std 5.38) mmHg and the average rigidity coefficient was 0.01013 (std 0.039)μl-1, the IOP measured by the GAT was 13.9 (std 3.23) mmHg. The statistical analysis indicated a significant statistical difference (p=9*10-8) between the two devices. Conclusion Significant errors of the measurement are related to the centration of the optical head and the hand driven indentation. To overcome these limitations the device was upgraded with the addition of a coaxial camera for centration control and a microstepping motor for the applanation movement. An investigation of the accuracy and repeatability of the system with these new additions is underway.

Purpose The wavelength dependence of the light scattering is related with the characteristics of the inhomogeneities in the ocular media, and therefore, an objective assessment could be used to the early detection of underlying ocular pathologies. We developed a new optical instrument for measuring light scattered in the human eye at different wavelengths. Methods Using a double-pass configuration, series of disks of uniform radiance with an increasing angular dimension are sequentially projected on to the retina. As a light source, a white light halogen lamp is spectrally filtered by using a liquid crystal tunable filter, selecting three different wavelengths: 550, 600 and 650 nm (FWHM = ± 50 nm). The disk’s retinal images are recorded by a cooled electron-multiplied CCD camera. The derivative of intensity at the center of each disk’s retinal image with respect to its radius provides the eye’s wide-angle double-pass point-spread function (PSF). The method was applied in an artificial eye with different levels of induced scattering, and in a group of normal subjects. Results In the artificial eye, the increasing scattering induced is successfully discriminated at the more eccentric angular domain of the wide-angle PSFs. In the group of subjects, the estimated wide-angle PSFs differ from the lower to the larger wavelengths. The PSF at 550 nm is characterized by more intense light scatter in the angular range between 5 and 10 degrees, while the PSF at the 650nm showed a relatively increased scattered light between 0 and 2 degrees. This would be related to the deeper interaction of th Conclusion An optical objective method is sensitive enough to detect consistently differences in light scatter for different wavelengths.

Purpose The intraocular pressure (IOP) is determined by a dynamic equilibrium between the production and the outflow of the aqueous humor. The dependence of outflow facility on IOP may be related to the biomechanical properties of the eye. This study examines the relationship between the outflow facility and IOP for the living human eye using an invasive manometric device. Methods An intraoperative invasive manometric device was used to measure the IOP of fifty four eyes from fifty four cataract patients. The measurements were performed before cataract surgery. The anterior chamber of the eye was cannulated to a microstepping pump and the pressure was recorded by a pressure transducer through special developed computer software. The IOP was artificially increased to 40 mmHg by infusion of BSS in the anterior chamber of the eye. The IOP decay curve was recorded. A mathematical model was developed to calculate the outflow facility coefficient. Results The average outflow facility coefficient was 0.328 (SD 0.093) μl/min/mmHg. From the data analysis the outflow facility coefficient was proved to have a non linear correlation with IOP. This non linear behavior of outflow facility was approximated with an exponential mathematical model. Conclusion The invasive method of measuring in vivo outflow facility coefficient employed in this study, avoiding the errors of tonography may provide accurate data on the dependence of outflow facility coefficient on IOP. These data, in conjunction with ocular rigidity measurements may facilitate our understanding of the relationship between the biomechanical properties of the eye and the anatomical changes in the trabecular area at elevated IOP levels.

PURPOSE: Seven existing and three new image quality metrics were evaluated in terms of their effectiveness in predicting subjective cycloplegic refraction. METHODS: Monochromatic wavefront aberrations (WA) were measured in 70 eyes using a Shack-Hartmann based device (Complete Ophthalmic Analysis System; Wavefront Sciences). Subjective cycloplegic spherocylindrical correction was obtained using a standard manifest refraction procedure. The dioptric amount required to optimize each metric was calculated and compared with the subjective refraction result. Metrics included monochromatic and polychromatic variants, as well as variants taking into consideration the Stiles and Crawford effect (SCE). WA measurements were performed using infrared light and converted to visible before all calculations. RESULTS: The mean difference between subjective cycloplegic and WA-derived spherical refraction ranged from 0.17 to 0.36 diopters (D), while paraxial curvature resulted in a difference of 0.68 D. Monochromatic metrics exhibited smaller mean differences between subjective cycloplegic and objective refraction. Consideration of the SCE reduced the standard deviation (SD) of the difference between subjective and objective refraction. CONCLUSIONS: All metrics exhibited similar performance in terms of accuracy and precision. We hypothesize that errors pertaining to the conversion between infrared and visible wavelengths rather than calculation method may be the limiting factor in determining objective best focus from near infrared WA measurements.