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To analyze transepithelial phototherapeutic keratectomy (PTK) results using optical coherence tomography (OCT) and develop a model to guide the laser dioptric and depth settings.Casey Eye Institute, Portland, Oregon, USA.Prospective nonrandomized case series.Patients with superficial corneal opacities and irregularities had transepithelial PTK with a flying-spot excimer laser by combining wide-zone myopic and hyperopic astigmatic ablations. Optical coherence tomography was used to calculate corneal epithelial lenticular masking effects, guide refractive laser settings, and measure opacity removal. The laser ablation efficiency and the refractive outcome were investigated using multivariate linear regression models.Twenty-six eyes of 20 patients received PTK to remove opacities and irregular astigmatism due to scar, dystrophy, radial keratotomy, or previous corneal surgeries. The uncorrected distance visual acuity and corrected distance visual acuity were significantly improved (P .01) by 3.7 Snellen lines and 2.0 Snellen lines, respectively, to a mean of 20/41.2 and 20/22.0, respectively. Achieved laser ablation depths were 31.3% (myopic ablation) and 63.0% (hyperopic ablation) deeper than the manufacturer's nomogram. The spherical equivalent of the corneal epithelial lenticular masking effect was 0.73 diopter ± 0.61 (SD). The refractive outcome highly correlated to the laser settings and epithelial lenticular masking effect (Pearson R = 0.96, P .01). The ablation rate of granular dystrophy opacities appeared to be slower. Smoothing ablation under masking fluid was needed to prevent focal steep islands in these cases.The OCT-measured ablation depth efficiency could guide opacity removal. The corneal epithelial lenticular masking effect could refine the spherical refractive nomogram to achieve a better refractive outcome after transepithelial ablation.

Purpose To distinguish between corneal ectasia and contact lens–related warpage by characteristic patterns on corneal topography and optical coherence tomography (OCT) epithelial thickness maps. Setting Casey Eye Institute, Portland, Oregon, USA. Design Prospective and retrospective case series. Methods Axial and mean power maps were obtained on corneal topography systems. Epithelial thickness maps were generated using RTVue OCT. A sector divider was applied to all maps. The locations of the minimum epithelial thickness, maximum epithelial thickness, maximum axial power, and maximum mean power were determined based on sector averages. Agreement was defined as the extremums occurring in the same or adjacent sectors. Results Twenty-one eyes with keratoconus, 6 eyes with forme fruste keratoconus (better eye of asymmetric keratoconus), and 15 eyes with contact lens–related warpage were identified. The keratoconus and forme fruste keratoconus eyes had coincident topographic steepening with epithelial thinning. The locations of minimum epithelial thickness and maximum axial power agreed in 90% of the keratoconic eyes, while the minimum epithelial thickness and maximum mean power agreed in 95% of them. Conversely, the warpage eyes had coincident topographic steepening with epithelial thickening and normal pachymetry maps. The locations of maximum epithelial thickness and maximum axial power agreed in 93% of the warpage eyes, while the maximum epithelial thickness and maximum mean power agreed in all warpage eyes. Conclusion Results show that epithelial thickness maps and corneal topographic maps are powerful synergistic tools in evaluating eyes with abnormal topography and can help differentiate between keratoconus and nonectatic conditions.

PURPOSE Using Scheimpflug tomography to investigate the difference in corneal power and corneal astigmatism between 3- and 4-mm diameter zones centered on the pupil and corneal apex. METHODS A total of 90 eyes were included in this study. Axial keratometry, total refractive power, and true net power centered on the pupil and corneal apex in 3- and 4-mm diameter zones were assessed. The paired sample t test and independent sample t test were used for data comparison. RESULTS For corneal power and corneal astigmatism for the 3- and 4-mm diameter zones, the flat K values of axial keratometry, total refractive power, and true net power centered on the pupil (3-mm: 43.99 ± 1.69 D, 43.12 ± 1.71 D, 42.53 ± 1.67 D; 4-mm: 44.04 ± 1.67 D, 43.38 ± 1.71 D, 42.61 ± 1.65 D) were significantly higher than those centered on the apex (3-mm: 43.93 ± 1.69 D, 43.05 ± 1.71 D, 42.46 ± 1.67 D; 4-mm: 44.01 ± 1.67 D, 43.34 ± 1.69 D, 42.58 ± 1.65 D; all P < 0.02). However, the steep K and astigmatism magnitude values centered on the pupil (3-mm: 45.71 ± 1.73 D, 45.01 ± 1.73 D, 44.38 ± 1.69 D; 1.72 ± 0.83 D, 1.89 ± 0.86 D, 1.85 ± 0.84 D; 4-mm: 45.78 ± 1.73 D, 45.28 ± 1.74 D, 44.45 ± 1.68 D; 1.73 ± 0.84 D, 1.90 ± 0.85 D, 1.84 ± 0.85 D) were lower than those centered on the apex (3-mm: 45.81 ± 1.74 D, 45.10 ± 1.72 D, 44.50 ± 1.70 D; 1.88 ± 0.90 D, 2.05 ± 0.90 D, 2.04 ± 0.90 D; 4-mm: 45.85 ± 1.73 D, 45.34 ± 1.73 D, 44.51 ± 1.69 D; 1.83 ± 0.88 D, 2.00 ± 0.90 D, 1.93 ± 0.86 D; all P < 0.01). Compared with the 3-mm diameter zone, the corresponding 4-mm diameter zone showed higher corneal power centered on both pupil and corneal apex. CONCLUSIONS The difference in corneal power and corneal astigmatism, measured at 3 and 4 mm, centered on the pupil and the corneal apex should be noted in corneal refractive surgery and toric intraocular lens calculation.

Purpose To compare the newer formulae, the optical coherence tomography (OCT)-based intraocular lens (IOL) power formula (OCT formula) and the Barrett True-K formula (True-K), with the methods on the American Society of Cataract and Refractive Surgery (ASCRS) calculator in eyes with previous myopic LASIK/photorefractive keratectomy (PRK). Design Prospective case series. Participants A total of 104 eyes of 80 patients who had previous myopic LASIK/PRK and subsequent cataract surgery and IOL implantation. Methods By using the actual refraction after cataract surgery as target refraction, predicted IOL power for each method was calculated. The IOL prediction error (PE) was obtained by subtracting the predicted IOL power from the power of the IOL implanted. Main Outcome Measures Arithmetic IOL PEs, variances of mean arithmetic IOL PE, median refractive PE, and percent of eyes within 0.5 diopters (D) and 1.0 D of refractive PE. Results Optical coherence tomography produced smaller variance of IOL PE than did Wang-Koch-Maloney (WKM) and Shammas ( P P Conclusions The OCT and True-K No History are promising formulas. The ASCRS IOL calculator has been updated to include the OCT and Barrett True K formulas. Trial registration: Intraocular Lens Power Calculation After Laser Refractive Surgery Based on Optical Coherence Tomography (OCT IOL); Identifier: NCT00532051; www.ClinicalTrials.gov.

Purpose. To quantify corneal epithelial thickness changes after myopic LASIK by OCT.Methods.Epithelial thickness before and after myopic LASIK were measured by a Fourier-domain OCT system. Average central (within 1 mm diameter) and paracentral epithelial thickness (5~6 mm diameter) before and after LASIK were compared. Correlation between central epithelial thickness change and laser spherical equivalent setting was evaluated. An epithelial smoothing constant was estimated based on a mathematical model published previously.Results.Nineteen eyes from 11 subjects were included in the study. Eyes had myopic LASIK ranging from −1.69 D to −6.75 D spherical equivalent. The average central epithelial thickness was 52.6 ± 4.1 μm before LASIK and 56.2 ± 4.3 μm 3 months after LASIK (p=0.002). The average paracentral epithelial thickness was 51.6 ± 6.6 μm before LASIK and 54.8 ± 4.3 μm 3 months after LASIK (p=0.007). The change in average central epithelial thickness was correlated with laser spherical equivalent (R2= 0.40,p=0.028). The epithelial smoothing constant was estimated to be 0.46 mm.Conclusions. Corneal epithelial thickens centrally and paracentrally after myopic LASIK. The extent of epithelial remodeling correlated with the amount of LASIK correction and could be predicted by a mathematical model.

Irradiated corneal tissues have been used for a variety of ophthalmic procedures including glaucoma drainage device covers and lamellar grafts. The maintenance of corneal clarity is important, as light obstructions resulting from processing or long-term storage of irradiated corneas may negatively affect vision and postoperative cosmesis. It has been reported that corneal tissues can be preserved in human serum albumin (HSA), however, the clarity of corneas after long-term storage in HSA has not been well described. Furthermore, the use of donor-pooled serum increases the risk for transmission of blood-borne diseases and may induce an immune response in the recipient. Here, we examined changes in corneal clarity due to electron-beam (e-beam) irradiation and storage in a recombinant human serum albumin (rHSA). Dark-field microscopy was employed to examine the light scattering effects of fresh and irradiated corneas. Compared to measurements taken prior to tissue preparation and e-beam treatment, irradiated corneas showed an average 2.6% increase in light scattering (P = 0.002). Irradiated corneas stored in rHSA at room-temperature for 20 months showed an average increase of 11.6% light scattering compared to fresh corneas (P ≪ 0.01), but did not negatively affect the visualization of printed text, and were deemed suitable for transplant use. Therefore, the slight increase in cornea light scattering, and resulting reduction in corneal clarity, after e-beam treatment and long-term storage in rHSA may not be clinically significant. These results suggest that e-beam sterilized corneal grafts may be used as an alternative to fresh tissue for certain ophthalmic applications.

To use Fourier-domain optical coherence tomography (OCT) to measure the angle opening distance at Schwalbe's line (AOD-SL) and determine its value in anterior chamber angle assessment.Horizontal scans of the nasal and temporal anterior chamber angles in glaucoma subjects were performed at 830 nm wavelength Fourier-domain OCT. Images were graded by 2 ophthalmologists who assessed the visibility of Schwalbe's line (SL), anterior limbus (AL), scleral spur (SS), and angle recess (AR). AOD-SL was measured with computer calipers. SL was manually identified by the termination of the corneal endothelium. Gonioscopy was used to classify anterior chamber angles according to a modified Shaffer system. Spearman ρ analysis was performed to assess correlation between AOD-SL and modified Shaffer grade. A cutoff value of AOD-SL for diagnosing occludable angles (modified Shaffer grade ≤ 1) was determined by receiver operating characteristic (ROC) analyses.Thirty-five glaucoma subjects (65 eyes) were enrolled. SL, AL, AR, and SS were visible by OCT in 97.7%, 99.2%, 87.3%, and 80.8% of eyes, respectively. Nasal and temporal AOD-SLs were 322.6 ± 200.2 µm and 341.4 ± 197.4 µm, respectively. Correlation coefficients between AOD-SL and modified Shaffer grade were 0.80 (nasal) and 0.81 (temporal). The diagnostic cutoff value of AOD-SL for occludable angles was 290 µm. The areas under the ROC curve, sensitivity, specificity values were 0.90, 0.80, 0.87 (nasal) and 0.90, 0.85, 0.77 (temporal), respectively.The measurement of AOD-SL by Fourier-domain OCT is highly correlated with gonioscopy and may be a useful noncontact method for assessing angle closure risk.

Purpose To use Fourier-domain optical coherence tomography (OCT) to measure corneal power and calculate intraocular lens (IOL) power in cataract surgeries after laser vision correction. Setting Doheny Eye Institute, Los Angeles, California, and Cullen Eye Institute, Houston, Texas, USA. Design Prospective comparative case series. Methods Patients with previous myopic laser vision correction who had monofocal IOL implantation were enrolled. A Fourier-domain OCT system was used to measure corneal power and pachymetry. Axial length and anterior chamber depth were measured with partial coherence biometry. An OCT-based IOL formula was developed, and the mean absolution error (MAE) of postoperative refraction was compared with that for the Haigis-L formula. At Doheny, corneal power was also measured using the clinical history method, the contact lens overrefraction method, and slit-scanning tomography total optical power. Results Sixteen eyes of 16 patients were enrolled at the 2 sites. Previous laser vision correction ranged from −9.81 to −0.88 diopter (D). The MAE was 0.50 D for OCT-based IOL calculation and 0.76 D for the Haigis-L formula ( P =.14). In the 6 eyes enrolled at Doheny, the MAE of OCT-based IOL calculation was 0.60 D. In comparison, the contact lens overrefraction (MAE = 1.46 D, P P P >.05). Conclusion The predictive accuracy of OCT-based IOL power calculation was equal to or better than current standards in post-laser vision correction eyes. Financial Disclosures Drs. Tang, Li, and Huang receive grant support from Optovue Inc., Fremont, California, USA. Dr. Huang received patent royalty, stock options, travel support, and speaker honorarium from Optovue, Inc., and receives patent royalty from the Massachusetts Institute of Technology related to optical coherence tomography technology licensed to Carl Zeiss Meditec, Inc. Dr. Wang received research support from Ziemer USA, Inc., Alton, Illinois, USA. Dr. Koch is a consultant to Alcon Surgical, Inc., Fort Worth, Texas, USA.

BACKGROUND AND OBJECTIVE: To compare Asian and Caucasian anterior segment dimensions measured by optical coherence tomography (OCT). PATIENTS AND METHODS: Anterior segment OCT images were obtained in normal subjects. Four line scans were acquired at the 90°, 45°, 0°, and 135° meridians of each eye. Computer calipers acquired anterior segment dimensions of corneal diameter, anterior chamber width, corneal vault, and anterior chamber depth on OCT images. Univariate and multivariate analyses were performed to assess correlations. RESULTS: Corneal diameter was 0.5 mm narrower ( P < .01), anterior chamber width was 0.46 mm narrower ( P < .01), and corneal vault was 0.22 mm lower ( P < .01) in Asian eyes. All anterior segment dimensions decreased with age. CONCLUSION: Asian eyes had smaller anterior segments compared to Caucasian eyes. Regardless of race, anterior segment dimensions were smaller in older subjects. Age-related changes may affect the tolerability of long-term implants such as phakic intraocular lenses.

To evaluate optical coherence tomography (OCT) in the measurement of donor corneas in preparation for endothelial keratoplasty.Donor corneas were imaged by OCT while immersed in preservation medium. Central corneal thickness (CCT) was measured by OCT from the Bowman layer to the endothelium. The corneas were then mounted on an artificial anterior chamber, and the epithelium was removed. Ultrasound pachymetry (USP) was used to measure CCT just before sectioning with a microkeratome. The central graft thickness (CGT) was measured by USP. The graft was then returned to the medium and imaged by OCT.The study included 154 donor corneas. The average CCT measured by OCT (550 ± 63 μm) was thicker (P0.001) than that measured by USP (507 ± 54 μm). Similarly, the CGT measured by OCT (158 ± 41 μm) was thicker (P = 0.0005) than that measured by USP (153 ± 38 μm). The predictability of cut depth, as assessed by pooled standard deviation (SD), was better (P = 0.023) for USP (41 μm) compared with OCT (48 μm). The graft was thicker (P0.001) peripherally than centrally in OCT images. The predictability of cut depth by OCT was better (P0.001) for corneas thinner than 600 μm (SD = 45.6 μm) compared with those thicker than 600 μm (SD = 86.9 μm).The donor corneal measurements by OCT were not as predictable as those by USP. The predictability of graft thickness, however, could be optimized using OCT to select for corneas thinner than 600 μm and then using immediate precut USP to set the microkeratome depth. A graft thickness profile measured by OCT could be useful to the surgeon.

Purpose To use optical coherence tomography (OCT) to measure corneal power and calculate intraocular lens (IOL) power in cataract surgeries after myopic and hyperopic laser vision correction (LVC). Methods Patients with previous LVC were enrolled in this prospective study at two centers (Doheny Eye Institute, Los Angeles, CA, USA and Cullen Eye Institute, Houston, TX, USA). Corneal power was measured with a Fourier-domain OCT system. The intravisit repeatability of OCT corneal power measurement was evaluated by the pooled standard deviation of repeat scans. Axial length, anterior chamber depth, and automated keratometry were measured with the IOLMaster. An OCT-based IOL formula was developed. The mean absolute error (MAE) of refractive prediction for OCT-based IOL formula was calculated. The results were compared with the MAE for Haigis-L formula. Results A total of 31 eyes of 24 subjects who had uncomplicated cataract surgery with monofocal IOL implantation were enrolled in the two sites. Twenty-two eyes of 16 subjects had previous myopic LVC that ranged from −12.46D to −0.88D. Nine eyes of 8 subjects had previous hyperopic LVC that ranged from 0.66D to 5.52D. The intravisit repeatability of OCT corneal power measurement was 0.24D. For the myopic LVC group, the OCT formula had a MAE of 0.57D compared to an MAE of 0.73D for the Haigis-L formula ( p =0.19). For the hyperopic LVC group, the MAE for OCT and Haigis-L formula was 0.26D and 0.54D, respectively ( p >0.05). Conclusions Corneal power can be precisely measured with OCT. The predictive accuracy of OCT-based IOL power calculation is equal to current standards for post-LVC eyes.

To measure the wound geometry after femtosecond laser-enabled keratoplasty (FLEK) using optical coherence tomography (OCT).Prospective nonrandomized clinical study and laboratory study.Patients who were candidates for penetrating keratoplasty at an academic referral center.Wound architecture was measured and analyzed by OCT in 8 eyes of 8 consecutive patients who underwent FLEK. Femtosecond laser lamellar cuts were performed on 3 eye bank corneas, and the wound diameters were measured by OCT.Sutures were completely removed on average at 1 month per decade of age after surgery. No cases of wound dehiscence were noted, and graft-host tissue apposition appeared excellent on OCT. The mean spectacle-corrected visual acuity 1 month after suture removal was 20/35, and mean astigmatism was 5.0 diopters by manifest refraction and 8.7 diopters by computerized topography. The measured graft diameter was smaller than the laser setting by 2.5% (P = 0.007). The cut diameters of the eye bank corneas were also slightly smaller than the laser setting.FLEK offers benefits of rapid wound healing and predictable wound geometry. The measured wound geometry agreed well with laser setting other than a small systematic deviation that could be explained by the mechanics of corneal applanation during the laser cut. OCT is a useful tool to measure the actual graft diameter after FLEK.

Purpose To evaluate the repeatability of Fourier-domain optical coherence tomography (OCT) measurements of the thickness of femtosecond laser–created laser in situ keratomileusis (LASIK) flaps. Setting Doheny Eye Institute, University of Southern California, Los Angeles, California, USA. Design Case series, evaluation of diagnostic technology. Methods In this consecutive series, Fourier-domain OCT (RTVue) was used to measure flap thickness 1 week after LASIK. Flaps were created with a Pulsion 60 kHz femtosecond laser programmed for 110 μm flap thickness. Each eye was scanned 2 times with a radial pachymetry pattern and 1 time with a horizontal line scan. Flap thicknesses were measured at 6 positions across the corneal flap (ie, ±0.5 mm, ±1.5 mm, and ±2.5 mm from the center on the horizontal and vertical meridians). The within-grader flap thickness repeatability and between-grader reproducibility were calculated by pooled standard deviations (SDs). Results Twenty-one eyes were measured. The mean flap thickness measurements were highly predictable at all positions. Thickness SDs varied from 5.3 to 9.5 μm and uniformity, from 121.7 to 126.5 μm. The within-grader repeatability was 3.3 to 6.4 μm based on the same image measured at different times and 4.7 to 7.4 μm for different images. The between-grader reproducibility was 4.0 to 9.0 μm. There was no statistically significant asymmetry between the nasal side and the temporal side, the superior side and the inferior side, or the pericentral area and the central area of the corneal flap. Conclusions The femtosecond laser created LASIK flaps with uniform and predictable thicknesses. Fourier-domain OCT gave highly repeatable flap-thickness measurements. Financial Disclosure Drs. Rosas Salaroli, Zhang, Branco Ramos, and Allemann have no financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes.

Laser in situ keratomileusis (LASIK) and other laser vision correction procedures are popular surgical options for the correction of myopia, astigmatism, and hyperopia. An unfortunate consequence of laser vision correction is the difficulty it creates for accurately calculating intraocular lens (IOL) power for cataract surgery.1,2 Increasingly, people who have had laser vision correction will face this problem as they age and develop cataracts. Theoretic formulae, including SRK/T, Hoffer Q, and Holladay II, are the current standards for calculating IOL power, and each works well on eyes that have not had keratorefractive surgery. The achieved refractions after cataract surgery are mostly within 0.50 diopters (D) of the target refraction.3–5 Three biometric parameters are essential in these formulae: axial length, corneal power, and IOL depth (or effective lens position [ELP]). The IOL depth cannot be known before surgery and is predicted by its statistical association with other biometric parameters.6 Prior laser vision correction introduces error in corneal power measurement. The corneal power is determined by both anterior and posterior corneal surfaces. However, conventional methods for measuring corneal power, such as manual keratometry, automated keratometry, and Placido-ring topography, measure only the anterior surface. The posterior corneal power is extrapolated by assuming a fixed relationship between the anterior and posterior curvatures. This assumption is implicit in the use of a fixed keratometric index to convert anterior corneal curvature to a dioptric corneal power value.7 The assumption does not hold in eyes after laser vision correction, which alters the anterior curvature but leaves the posterior surface unchanged.8–10 After myopic laser vision correction, conventional keratometry overestimates corneal power, which could lead to a biased IOL calculation and a hyperopic outcome after cataract surgery.11,12 The trend is opposite for patients with prior hyperopic laser vision correction.13 Corneal tomography systems can measure the posterior corneal power. Both slit-scanning tomography and rotating Scheimpflug-camera imaging have been used for this purpose.14–19 These devices provide convenient alternative methods to calculate IOL power for eyes with prior laser vision correction. These alternatives are particularly valuable when preoperative refractive surgery data are not available. In addition to these devices, optical coherence tomography (OCT) can also be used to measure posterior corneal power. Tang et al20 recently reported good repeatability and accuracy when using OCT to measure total corneal power. Compared to other types of corneal tomography, OCT has higher axial resolution and better accuracy in corneal measurement in the presence of opacities.21 In this article, we report the development of an OCT-based IOL formula and study its accuracy in a series of cataract surgery patients without prior laser vision correction.

To evaluate the repeatability of Fourier-domain optical coherence tomography (OCT) pachymetric mapping and compare central corneal thickness (CCT) measurements by OCT, ultrasound pachymetry, and scanning-slit tomography.Doheny Eye Institute, University of Southern California, Los Angeles, California, USA.A Fourier-domain OCT system was used to map the corneal thickness in normal eyes with scans centered on the corneal vertex or the pupil. Repeatability of central and pericentral map sectors was assessed by pooled standard deviation. The CCT measurements were compared between the OCT, ultrasound, and scanning-slit devices.Pupil centration (SD: 1.3 microm central, 1.8 to 3.8 microm pericentral) provided better repeatability than vertex centration (SD: 1.7 microm central, 2.4 to 5.7 microm pericentral) in all sectors (P.035). The mean CCT was 536.9 microm +/- 27.0 (SD) by OCT, 556.6 +/- 30.5 microm by ultrasound, and 537.2 +/- 32.6 microm by scanning-slit tomography (acoustic factor 0.92). The CCT measured by OCT was significantly thinner than by ultrasound pachymetry (P = .007; mean difference -19.7 microm; 95% limits of agreement [LoA], -40.4 to 0.9 microm) but not than by scanning-slit tomography (P = .2637; mean difference -0.3 microm; 95% LoA, -24.0 to 23.5 microm). The CCT by OCT correlated well with ultrasound and scanning-slit CCTs (r = 0.940 and r = 0.934, respectively).Pachymetric mapping with Fourier-domain OCT was highly repeatable. Repeatability was better with pupil-centered scans than with corneal vertex-centered scans. Ultrasound pachymetry, Fourier-domain OCT, and scanning-slit tomography should not be used interchangeably for CCT assessment.

PURPOSE To use optical coherence tomography (OCT) to detect previous refractive surgery in donor corneas. METHODS We constructed a tabletop OCT scanner operating at 1310-nm wavelength. Donor corneas at the Cleveland Eye Bank were scanned while sealed within the sterile container immersed in Optisol GS. OCT scanning was performed with 7.6-mm-long lines (512 axial scans) along 8 meridians. Anterior and posterior corneal surfaces were automatically mapped using image processing software that we developed. Curvature was computed from the best parabolic fit in the central 5-mm diameter. Layered analysis of the stromal reflectivity was also performed. Twenty-nine corneas from 19 donors were examined. Five had a history of laser in situ keratomileusis (LASIK). RESULTS The flap interfaces could not be visualized on slit-lamp or OCT images but were confirmed by histology. The death-to-scan time was 22.1 +/- 11.4 (SD) hours for normal corneas and 100.6 +/- 57.5 hours for LASIK corneas. The anterior surface power was 67.5 +/- 2.5 D in control corneas and 64.5 +/- 2.4 D in LASIK corneas (P = 0.023). There was no significance between the 2 groups in terms of posterior curvature and thickness parameters. The anterior/posterior reflectivity ratio in the central 4-mm diameter was significantly lower in post-LASIK corneas than in control (P < 0.05). CONCLUSIONS OCT provides thickness, topography, and reflectivity maps of donor corneas without taking them out of preservation medium and container. The anterior curvature and the anterior/posterior stromal reflectivity ratio may be useful for detecting previous LASIK.

Purpose To investigate intrastromal corneal ring segment depth with a high-speed corneal optical coherence tomography (OCT) system. Setting Doheny Eye Institute, University of Southern California, Los Angeles, California, USA. Methods A prospective observational case series comprised 4 eyes of 4 patients receiving Intacs intrastromal corneal ring segments (Addition Technology, Inc.) for keratoconus. Optical coherence tomography (OCT) was performed between 7 days and 43 days after implantation. Results The slitlamp impression of intrastromal corneal ring segment implantation depth did not correlate well with OCT measurements ( r 2 = 0.68). The fractional implantation depth was correlated with several surgical variables using a stepwise multivariate regression model, and 2 statistically significant correlations were found. The position of the distal portions of the ring segments was shallower than that of the portion closer to the insertion site ( P = .003). Segments placed in the inferior cornea ( P = .008) experienced more distal shallowing. Shallower depth was associated with greater fractional anterior stromal compression ( P = .04). Conclusions Shallower placement of intrastromal corneal ring segments may result in more complications, such as epithelial–stromal breakdown and extrusion, because of the greater anterior stromal tensile strain. The distal and inferior portions of intrastromal corneal ring segments tended to be placed at a shallower depth. Optical coherence tomography provided precise measurement of ring segment depth and may help identify implants that pose a greater risk for depth-related complications.

Purpose To develop an optical coherence tomography (OCT) pachymetry map–based keratoconus risk scoring system. Settings Doheny Eye Institute, University of Southern California, Los Angeles, California, and Brass Eye Center, New York, New York, USA; Department of Ophthalmology, Affiliated Eye Hospital of Wenzhou Medical College, Wenzhou, China. Design Cross-sectional study. Methods Fourier-domain OCT was used to acquire corneal pachymetry maps in normal and keratoconus subjects. Pachymetric variables were minimum, minimum−median, superior–inferior (S–I), superonasal–inferotemporal (SN–IT), and the vertical location of the thinnest cornea (Ymin). A logistic regression formula and a scoring system were developed based on these variables. Keratoconus diagnostic accuracy was measured by the area under the receiver operating characteristic (ROC) curve. Results One hundred thirty-three eyes of 67 normal subjects and 82 eyes from 52 keratoconus subjects were recruited. The keratoconus logistic regression formula = 0.543 × minimum + 0.541 × (S–I) − 0.886 × (SN–IT) + 0.886 × (minimum–median) + 0.0198 × Ymin. The formula gave better diagnostic power with the area under the ROC than the best single variable (formula = 0.975, minimum = 0.942; P P =.08). Conclusion The OCT corneal pachymetry map–based logistic regression formula and the keratoconus risk scoring system provided high accuracy in keratoconus detection. These methods may be useful in keratoconus screening. Financial Disclosure Oregon Health and Science University (OHSU) and Drs. Huang, Li, and Tang have a significant financial interest in Optovue, Inc., a company that may have a commercial interest in the results of this research and technology. These potential conflicts of interest has been reviewed and managed by OHSU. Dr. Brass receives speaker honoraria from Optovue, Inc. No other author has a financial or proprietary interest in any material or method mentioned.

Author(s): Tang, Maolong; Li, Yan; Chamberlain, Winston; Louie, Derek J; Schallhorn, Julie M; Huang, David | Abstract: PurposeTo differentiate between keratoconus and contact lens-related corneal warpage by combining focal change patterns in anterior corneal topography, pachymetry, and epithelial thickness maps.MethodsPachymetry and epithelial thickness maps of normal, keratoconus, and warpage, and forme fruste keratoconus (FFK) eyes were obtained from a Fourier-domain optical coherence tomography (OCT). Epithelial pattern standard deviation (PSD) was calculated and combined with two novel indices, the Warpage Index and the Anterior Ectasia Index, to differentiate between normal, keratoconus, and warpage eyes. The values of the three parameters were compared between groups.ResultsThe study included 22 normal, 31 keratoconic, 11 warpage, and 8 FFK eyes. The epithelial PSD was normal (l 0.041) for 100% normal eyes and abnormal (g 0.041) for 100% of keratoconic eyes, 81.8% of warpage eyes, and 87.5% of FFK eyes. The Anterior Ectasia Index of normal eyes (1.66 ± 0.74) was significantly lower than that for the keratoconus eyes (17.5 ± 7.17), the warpage eyes (2.98 ± 1.69), and the FFK eyes (6.95 ± 5.86). The Warpage Index was positive in all warpage eyes and negative for all keratoconic and FFK eyes except three wearing rigid gas-permeable contact lens.ConclusionsThe epithelial PSD can distinguish normal from keratoconus or warpage, but does not distinguish between these two conditions. The Anterior Ectasia Index is abnormal in keratoconus but not warpage. The Warpage Index is positive for warpage and negative for keratoconus, except in cases where keratoconus and warpage coexist. Together, the three parameters are strong tripartite discriminators of normal, keratoconus, and warpage.

Purpose To evaluate the accuracy of the optical coherence tomography–based (OCT formula) and Barrett True K (True K) intraocular lens (IOL) calculation formulas in eyes with previous radial keratotomy (RK). Methods In 95 eyes of 65 patients, using the actual refraction following cataract surgery as target refraction, the predicted IOL power for each method was calculated. The IOL prediction error (PE) was obtained by subtracting the predicted IOL power from the implanted IOL power. The arithmetic IOL PE and median refractive PE were calculated and compared. Results All formulas except the True K produced hyperopic IOL PEs at 1 month, which decreased at ≥4 months (all P < 0.05). For the double-K Holladay 1, OCT formula, True K, and average of these three formulas (Average), the median absolute refractive PEs were, respectively, 0.78 diopters (D), 0.74 D, 0.60 D, and 0.59 D at 1 month; 0.69 D, 0.77 D, 0.77 D, and 0.61 D at 2 to 3 months; and 0.34 D, 0.65 D, 0.69 D, and 0.46 D at ≥4 months. The Average produced significantly smaller refractive PE than did the double-K Holladay 1 at 1 month (P < 0.05). There were no significant differences in refractive PEs among formulas at 4 months. Conclusions The OCT formula and True K were comparable to the double-K Holladay 1 method on the ASCRS (American Society of Cataract and Refractive Surgery) calculator. The Average IOL power on the ASCRS calculator may be considered when selecting the IOL power. Further improvements in the accuracy of IOL power calculation in RK eyes are desirable.

Purpose. To assess optical coherence tomography (OCT) for guiding design and fit of a prosthetic device for corneal disease.Methods. A prototype time domain OCT scanner was used to image the anterior segment of patients fitted with large diameter (18.5–20 mm) prosthetic devices for corneal disease. OCT images were processed and analyzed to characterize corneal diameter, corneal sagittal height, scleral sagittal height, scleral toricity, and alignment of device. Within-subject variance of OCT-measured parameters was evaluated. OCT-measured parameters were compared with device parameters for each eye fitted. OCT image correspondence with ocular alignment and clinical fit was assessed.Results. Six eyes in 5 patients were studied. OCT measurement of corneal diameter (coefficient of variation, %), cornea sagittal height (%), and scleral sagittal height (%) is highly repeatable within each subject. OCT image-derived measurements reveal strong correlation between corneal sagittal height and device corneal height () and modest correlation between scleral and on-eye device toricity (). Qualitative assessment of a fitted device on OCT montages reveals correspondence with slit lamp images and clinical assessment of fit.Conclusions. OCT imaging of the anterior segment is suitable for custom design and fit of large diameter (18.5–20 mm) prosthetic devices used in the treatment of corneal disease.

OCT can accurately map corneal, epithelial, stromal thicknesses, and measure corneal curvatures. It’s useful in keratoconus screening, intraocular lens power calculation, phototherapeutic keratectomy guidance, imaging of corneal diseases, surgeries (implantation and transplantation).

Background and objective: The aim of this laboratory study was to investigate an alternative corneal trephination technique, femtosecond laser-enabled keratoplasty (FLEK), for inserting and stabilizing the depth of a metallic alloy intrastromal corneal ring (ISCR) for penetrating keratoplasty (PKP). Patients and methods: The FLEK procedures were performed on eye bank corneas mounted on an artificial anterior chamber. An angled mushroom pattern cut formed an elbow to support 7.5- and 8.0-mm ISCRs at 300 μm depth. Optical coherence tomography (OCT) was used to visualize the position of the inserted ISCR. Results: OCT images showed that the diameters of the femtosecond laser cut patterns matched the size of the respective ISCRs. Both rings rested stably on the corneal rims even prior to suturing. After suturing, the depths for the 7.5-mm and 8.0-mm ISCRs were measured by OCT to be 301.0 μm and 299.5 μm, respectively. Conclusion: The angled mushroom pattern cut by femtosecond laser may improve the predictability and stability of the ISCR position within the wound in PKP performed by FLEK.

Purpose To study the accuracy and repeatability of anterior, posterior, and net corneal power measured by Fourier-domain optical coherence tomography (OCT). Setting Doheny Eye Institute, Los Angeles, California, USA. Design Cross-sectional study. Methods A Fourier-domain OCT system (RTVue) was used to scan normal eyes, eyes after myopic laser in situ keratomileusis (LASIK), and keratoconic eyes. After the corneal surfaces were delineated, the system calculated anterior and posterior corneal powers by curve fitting over the central 3.0 mm diameter area. Net corneal power was calculated using a thick-lens formula. The repeatability of the calculations was evaluated by the pooled standard deviation of 3 measurements from the same visit. The net corneal power values were compared with standard automated keratometry measurements (IOLMaster). Results The repeatability of Fourier-domain OCT net corneal power was 0.19 diopters (D), 0.26 D, and 0.30 D in the normal, post-LASIK, and keratoconus groups, respectively. The Fourier-domain OCT net corneal power was significantly lower than keratometry by a mean of −1.21 D, −2.89 D, and −3.07 D, respectively (P Conclusions Corneal power measured by Fourier-domain OCT achieved good repeatability in all 3 groups. The repeatability was better than slower time-domain OCT systems. Because Fourier-domain OCT directly measures both anterior and posterior corneal surfaces, it may produce more consistent results than standard keratometry in post-LASIK and keratoconic eyes in which the anterior–posterior corneal curvature ratios are altered by surgery or disease. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes.

Background and Objective:To study the reproducibility of tear meniscus measurement with high-speed high-resolution Fourier-domain optical coherence tomography (FD-OCT).Patients and Methods:Twenty normal participants were enrolled in this prospective study. The lower tear meniscus in the right eye of each subject was imaged by vertical scans centered on the inferior cornea and the lower eyelid using an FD-OCT system (RTVue; Optovue, Inc., Fremont, CA) with a corneal adaptor. The system performs 26,000 axial scans per second and has a 5-micron axial resolution. Each subject was examined at two visits 30 to 60 days apart. Each eye was scanned twice on each visit. The scans were taken 2 seconds after a blink. The lower meniscus height, depth, and cornea–meniscus angle were measured with a computer caliper. The cross-sectional area was calculated using a two-triangle approximation.Results:The between-visits coefficient of variation was 17.5%, 18.0%, 35.5%, and 12.2% for meniscus height, depth, area, and angle, respectively. The intraclass correlations for these parameters were 0.605, 0.558, 0.567, and 0.367, respectively.Conclusion:FD-OCT measures lower tear meniscus dimensions and area with higher between-visits reproducibility than previous OCT instruments. FD-OCT may be a useful way to measure dry eye severity and treatment effectiveness.

To detect abnormal corneal thinning in keratoconus using pachymetry maps measured by high-speed anterior segment optical coherence tomography (OCT).Cross-sectional observational study.Thirty-seven keratoconic eyes from 21 subjects and 36 eyes from 18 normal subjects.The OCT system operated at a 1.3 microm wavelength with a scan rate of 2000 axial scans per second. A pachymetry scan pattern (8 radials, 128 axial scans each; 10 mm diameter) centered at the corneal vertex was used to map the corneal thickness. The pachymetry map was divided into zones by octants and annular rings. Five pachymetric parameters were calculated from the region inside the 5 mm diameter: minimum, minimum-median, inferior-superior (I-S), inferotemporal-superonasal (IT-SN), and the vertical location of the thinnest cornea. The 1-percentile value of the normal group was used to define the diagnostic cutoff. Placido-ring-based corneal topography was obtained for comparison.The OCT pachymetric parameters and a quantitative topographic keratoconus index (keratometry, I-S, astigmatism, and skew percentage [KISA%]) were used for keratoconus diagnosis. Diagnostic performance was assessed by the area under the receiver operating characteristic (AROC) curve.Keratoconic corneas were thinner. The pachymetric minimum averaged 452.6+/-60.9 microm in keratoconic eyes versus 546+/-23.7 microm in normal eyes. The 1-percentile cutoff was 491.6 microm. The thinnest location was inferiorly displaced in keratoconus (-805+/-749 microm vs -118+/-260 microm; cutoff, -716 microm). The thinning was focal (minimum-median: -95.2+/-41.1 microm vs -45+/-7.7 microm; cutoff, -62.6 microm). Keratoconic maps were more asymmetric (I-S, -44.8+/-28.7 microm vs -9.9+/-9.3 microm; cutoff, -31.3 microm; and IT-SN, -63+/-35.7 microm vs -22+/-11.4 microm; cutoff, -48.2 microm). Keratoconic eyes had a higher KISA% index (2641+/-5024 vs 21+/-19). All differences were statistically significant (t test, P0.0001). Applying the diagnostic criteria of any 1 OCT pachymetric parameter below the keratoconus cutoff yielded an AROC of 0.99, which was marginally better (P = .09) than the KISA% topographic index (AROC, 0.91).Optical coherence tomography pachymetry maps accurately detected the characteristic abnormal corneal thinning in keratoconic eyes. This method was at least as sensitive and specific as the topographic KISA.Proprietary or commercial disclosure may be found after the references.

The authors report a case of post-LASIK interface fluid syndrome that led to epithelial ingrowth, a sequelae that had not been reported to date. The interface fluid was caused by steroid-induced ocular hypertension. On post-LASIK day 49, the interface fluid, epithelial ingrowth, and noncellular reflective deposits were visualized by confocal microscopy and high-resolution Fourier-domain optical coherence tomography. No inflammatory cells or infectious organisms were seen. These high-resolution imaging technologies were useful in the noninvasive evaluation of the location and nature of flap interface pathologies at the microstructural level. [Ophthalmic Surg Lasers Imaging; 2008;39:S80-S82.]

Purpose To study the architecture of clear corneal incisions for phacoemulsification cataract surgery using optical coherence tomography (OCT). Setting Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, California, USA. Methods This prospective study comprised 20 eyes of 20 patients 1 month after cataract surgery performed by 1 of 2 experienced surgeons. Temporal clear corneal single-plane incisions were made with 3.0 mm metal keratomes. Each eye was scanned before and 1 month after surgery with a prototype high-speed anterior segment OCT system (Carl Zeiss Meditec, Inc.). The OCT scans were repeated 3 times during the same visit. The length of the corneal incision, thickness of the cornea, and position of the incision (distance from external wound edge to scleral spur) were measured using a computer caliper. The angle of the incision relative to the corneal surface was then calculated. Results The mean corneal incision length was 1.81 mm ± 0.27 (SD), the mean corneal thickness at the incision was 747 ± 67μm, and the mean distance between the incision and the scleral spur was 1.46 ± 0.24 mm. The mean angle of the incision was 26.8 ± 5.5 degrees. The measurements were repeatable to within ±0.072 mm (pooled standard deviation) for the incision length, ±11 μm for the corneal thickness, and ±0.042 mm for the position of the incision. Conclusions Optical coherence tomography allowed excellent evaluation of corneal incisions in cataract surgery postoperatively. Measurements of wound dimensions using OCT were highly repeatable.

Purpose To evaluate corneal opacities with optical coherence tomography (OCT). Design Prospective observational case series. Participants Twenty-three eyes of 19 patients with corneal opacities referred to a tertiary medical center. Methods Twenty-three consecutive eyes with corneal opacities were imaged with a high-speed corneal OCT prototype (Carl Zeiss Meditec, Inc., Dublin, CA). The OCT system operates at a speed of 2000 axial scans per second and a wavelength of 1.3 μm. Slit-scanning tomography (Orbscan II, software version 3.12; Bausch & Lomb, Inc., Rochester, NY) and ultrasound pachymetry (Corneo-Gage Plus; Sonogage, Cleveland, OH) also were performed. Main Outcome Measures Central cornea thickness was measured by the 3 instruments. Results In eyes with central opacities (n = 17), OCT central cornea thickness measurements were statistically equivalent to ultrasound pachymetry, whereas Orbscan II measurements were significantly less than ultrasound pachymetry (difference, −132.7±143 μm; P = 0.006). The OCT and ultrasound pachymetry results were obtained for all eyes, whereas Orbscan was unable to provide readings in 4 eyes. In eyes with off-center opacities (n = 6), OCT and Orbscan II central cornea thickness measurements were statistically equivalent to ultrasound pachymetry. The OCT measurements of epithelial thickness and scar depth also were demonstrated. Conclusions Optical coherence tomography provides consistent pachymetry mapping, whereas Orbscan II significantly underestimates corneal thickness in the presence of central corneal scars. Optical coherence tomography could be valuable in the planning of surgical treatment of corneal scars.

To characterize keratoconus and pellucid marginal degeneration (PMD) on mean curvature maps.Observational case series.A retrospective analysis of clinical records of 19 keratoconus eyes and eight PMD eyes. Keratometric mean curvature maps were computed from a placido-disk-based corneal topography system. The peak location and amplitude of distortions were quantified by fitting two-dimensional Gaussian functions. Computer simulations of keratoconic corneal topography were used to help interpret the results.Keratoconus and PMD eyes had a characteristic localized increase in convexity (cone) on mean curvature maps. Computer simulations showed that the peak on the mean curvature map accurately represented the peak of the cone-like distortion. However, the peak location and appearance of the same conic distortion on axial and tangential maps were greatly influenced by coexisting astigmatism. The Gaussian function provided an excellent model of keratoconus on mean curvature maps, with a mean cross-correlation of 0.80. According to Gaussian fitting, the vertical cone peak locations were -1.10 +/- 0.43 mm (mean +/- SD) in keratoconus eyes and -1.94 +/- 0.53 mm in PMD eyes (P.01). The locations of peaks on axial and tangential maps differed considerably from those on mean curvature maps. Advanced keratoconus tended to have higher cones (amplitude 13.31 +/- 6.87 diopters) than early keratoconus (amplitude 10.65 +/- 1.56 diopters).Gaussian fitting of mean curvature maps accurately quantifies the peak location and amplitude of the cone in keratoconus and PMD eyes. This new topographic analysis might be useful in the diagnosis and tracking of corneal ectatic diseases.

Purpose To evaluate changes in anterior chamber (AC) morphology induced by cataract extraction using anterior segment optical coherence tomography (OCT). Design Prospective comparative observational case series. Methods Thirty-two eyes of 32 patients underwent OCT imaging of the angle before and after cataract surgery. Anterior chamber depth (ACD), angle opening distance at 500 μm (AOD 500 ) and trabecular-iris space at 500 μm (TISA 500 ) were measured pre- and postoperatively. Preoperative lens thickness (LT) and lens position (LP) were calculated. Results ACD, AOD 500 , and TISA 500 increased significantly after cataract extraction ( P P = .0083) as did ACD and TISA 500 ( P = .0001). TISA 500 correlated with LP ( P = .0001) but not with LT ( P = .74). Conclusions Changes in angle morphology after cataract surgery can be imaged and objectively quantified by anterior segment OCT. Lens position may have a greater influence on angle width than LT.