Ayeswarya Ravikumar

Wavefront-guided scleral lens correction in keratoconus.

Purpose To examine the performance of state-of-the-art wavefront-guided scleral contact lenses (wfgSCLs) on a sample of keratoconic eyes, with emphasis on performance quantified with visual quality metrics, and to provide a detailed discussion of the process used to design, manufacture, and evaluate wfgSCLs. Methods Fourteen eyes of seven subjects with keratoconus were enrolled and a wfgSCL was designed for each eye. High-contrast visual acuity and visual quality metrics were used to assess the on-eye performance of the lenses. Results The wfgSCL provided statistically lower levels of both lower-order root mean square (RMS) (p < 0.001) and higher-order RMS (HORMS) (p < 0.02) than an intermediate spherical equivalent scleral contact lens. The wfgSCL provided lower levels of lower-order RMS than a normal group of well-corrected observers (p << 0.001). However, the wfgSCL does not provide less HORMS than the normal group (p = 0.41). Of the 14 eyes studied, 10 successfully reached the exit criteria, achieving residual HORMS wavefront error less than or within 1 SD of the levels experienced by normal, age-matched subjects. In addition, measures of visual image quality (logVSX, logNS, and logLIB) for the 10 eyes were well distributed within the range of values seen in normal eyes. However, visual performance as measured by high-contrast acuity did not reach normal, age-matched levels, which is in agreement with prior results associated with the acute application of wavefront correction to keratoconic eyes. Conclusions Wavefront-guided scleral contact lenses are capable of optically compensating for the deleterious effects of higher-order aberration concomitant with the disease and can provide visual image quality equivalent to that seen in normal eyes. Longer-duration studies are needed to assess whether the visual system of the highly aberrated eye wearing a wfgSCL is capable of producing visual performance levels typical of the normal population.

Change in visual acuity is highly correlated with change in six image quality metrics independent of wavefront error and/or pupil diameter

It is well known that the wavefront error (WFE) of the eye varies from individual to individual with pupil diameter (PD) and age. Numerous studies have been proposed evaluating the relationship between visual acuity and WFE, but all these studies were performed with either a fixed or natural PD. It is still not clear if metrics of image quality correlate well with visual acuity independent of PD. Here we investigate the correlation between the change in visual acuity and the change in 30 image quality metrics for a range of optical quality typically established in normal eyes that varies both with age and PD. Visual acuity was recorded for 4 normal subjects using simulated blurred logMAR acuity charts generated from the point spread functions of different scaled WFEs for 6 different PDs (2-7 mm in 1 mm steps). Six image quality metrics (log neural sharpness, log visual Strehl [spatial domain], log visual Strehl [MTF method], log pupil fraction [tessellated], log pupil fraction [concentric area], and log root mean square of WFE slope) accounted for over 80% of variance in change in acuity across all WFEs and all PDs. Multiple regression analysis did not significantly increase the R(2). Simple metrics derived from WFE could potentially act as an objective surrogate to visual acuity without the need for complex models.

Six just-noticeable differences in retinal image quality in 1 line of visual acuity: Toward quantification of happy versus unhappy patients with 20/20 acuity

PURPOSE: To determine the number of just‐noticeable differences in wavefront blur necessary to induce a 1‐line loss of corrected distance visual acuity (CDVA). SETTING: Visual Optics Institute, College of Optometry, University of Houston, Houston, Texas, USA. DESIGN: Evidence‐based manuscript. METHODS: The 3.0 mm wavefront error of a well‐corrected average eye was scaled to yield 9 small steps of blur quantified in units of log visual Strehl (logVS). For each logVS value, 10 unique 3‐line acuity charts were generated. Using a temporal forced‐choice paradigm, subjects compared each test chart to a reference acuity chart and indicated which chart was blurrier. The difference between 80% and 50% on the psychometric function defined a just‐noticeable difference. The CDVA was measured up to fifth‐letter miss for several aberrated logMAR charts for 6 logVS values. The number of just‐noticeable differences necessary to lose 1 line of acuity was defined as the change in logVS necessary to lose 1 line of acuity divided by the 1 just‐noticeable difference in logVS. RESULTS: Linear regression showed that logVS = −2.98 × (logMAR acuity) − 0.31 (R 2 = 0.961). The mean just‐noticeable difference was 0.049 logVS ± 0.012 (SD), resulting in a mean of 6.1 just‐noticeable differences per line of logMAR acuity. CONCLUSIONS: The retinal image quality metric logVS was highly correlated with logMAR acuity. The 6 just‐noticeable differences in logVS before 1 line of acuity was lost may provide an objective explanation for the distinction between patients with 20/20 CDVA who are happy and patients with 20/20 CDVA who are unhappy and other aberration‐related clinical complaints when acuity is near normal. Financial Disclosure: Ms. Ravikumar, Ms. Shi, Dr.Applegate, and Dr. Bedell have no financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes.

Optimizing wavefront-guided corrections for highly aberrated eyes in the presence of registration uncertainty.

Dynamic registration uncertainty of a wavefront-guided correction with respect to underlying wavefront error (WFE) inevitably decreases retinal image quality. A partial correction may improve average retinal image quality and visual acuity in the presence of registration uncertainties. The purpose of this paper is to (a) develop an algorithm to optimize wavefront-guided correction that improves visual acuity given registration uncertainty and (b) test the hypothesis that these corrections provide improved visual performance in the presence of these uncertainties as compared to a full-magnitude correction or a correction by Guirao, Cox, and Williams (2002). A stochastic parallel gradient descent (SPGD) algorithm was used to optimize the partial-magnitude correction for three keratoconic eyes based on measured scleral contact lens movement. Given its high correlation with logMAR acuity, the retinal image quality metric log visual Strehl was used as a predictor of visual acuity. Predicted values of visual acuity with the optimized corrections were validated by regressing measured acuity loss against predicted loss. Measured loss was obtained from normal subjects viewing acuity charts that were degraded by the residual aberrations generated by the movement of the full-magnitude correction, the correction by Guirao, and optimized SPGD correction. Partial-magnitude corrections optimized with an SPGD algorithm provide at least one line improvement of average visual acuity over the full magnitude and the correction by Guirao given the registration uncertainty. This study demonstrates that it is possible to improve the average visual acuity by optimizing wavefront-guided correction in the presence of registration uncertainty.

Change in visual acuity is well correlated with change in image-quality metrics for both normal and keratoconic wavefront errors

We determined the degree to which change in visual acuity (VA) correlates with change in optical quality using image-quality (IQ) metrics for both normal and keratoconic wavefront errors (WFEs). VA was recorded for five normal subjects reading simulated, logMAR acuity charts generated from the scaled WFEs of 15 normal and seven keratoconic eyes. We examined the correlations over a large range of acuity loss (up to 11 lines) and a smaller, more clinically relevant range (up to four lines). Nine IQ metrics were well correlated for both ranges. Over the smaller range of primary interest, eight were also accurate and precise in estimating the variations in logMAR acuity in both normal and keratoconic WFEs. The accuracy for these eight best metrics in estimating the mean change in logMAR acuity ranged between ±0.0065 to ±0.017 logMAR (all less than one letter), and the precision ranged between ±0.10 to ±0.14 logMAR (all less than seven letters).

A Comparison of Three Methods to Increase Scleral Contact Lens On-Eye Stability.

Purpose: To quantify on-eye rotational and translational stability of three scleral contact lens stabilization methods and to model the variation in visual acuity when these movements occur in a wavefront-guided correction for highly aberrated eyes. Methods: Three lens stabilization methods were integrated into the posterior periphery of a scleral contact lens designed at the Visual Optics Institute. For comparison, a lens with no stabilization method (rotationally symmetric posterior periphery) was designed. The lenses were manufactured and lens movements were quantified on 8 eyes as the average SD of the observed translations and rotations over 60 min of wear. In addition, the predicted changes in acuity for five eyes with keratoconus wearing a simulated wavefront-guided correction (full correction through the fifth order) were modeled using the measured movements. Results: For each lens design, no significant differences in the translation and rotation were found between left and right eyes, and lenses behaved similarly on all subjects. All three designs with peripheral stability modifications exhibited no statistically significant differences in translation and rotation distributions of lens movement and were statistically more stable than the spherical lens in rotation. When the measured movements were used to simulate variation in visual performance, the 3 lenses with integrated stability methods showed a predicted average loss in acuity from the perfectly aligned condition of approximately 0.06 logMAR (3 letters), compared with the loss of over 0.14 logMAR (7 letters) for the lens with the spherical periphery. Conclusion: All three stabilization methods provided superior stability, as compared with the spherical lens design. Simulations of the optical and visual performance suggest that all three stabilization designs can provide desirable results when used in the delivery of a wavefront-guided correction for a highly aberrated eye.

Simulated Keratometry Repeatability in Subjects with and without Down Syndrome

Purpose To assess the repeatability of simulated keratometry measures obtained with Zeiss Atlas topography for subjects with and without Down syndrome (DS). Methods Corneal topography was attempted on 140 subjects with DS and 138 controls (aged 7–59 years). Subjects who had at least three measures in each eye were included in analysis (DS: n = 140 eyes (70 subjects) and controls: n = 264 eyes (132 subjects)). For each measurement, the steep corneal power (K), corneal astigmatism, flat K orientation, power vector representation of astigmatism (J0, J45), and astigmatic dioptric difference were determined for each measurement (collectively termed keratometry values here). For flat K orientation comparisons, only eyes with >0.50 DC of astigmatism were included (DS: n = 131 eyes (68 subjects) and control: n = 217 eyes (119 subjects)). Repeatability was assessed using (1) group mean variability (average standard deviation (SD) across subjects), (2) coefficient of repeatability (COR), (3) coefficient of variation (COV), and (4) intraclass correlation coefficient (ICC). Results The keratometry values showed good repeatability as evidenced by low group mean variability for DS versus control eyes (⩽0.26D vs. ⩽0.09D for all dioptric values; 4.51° vs. 3.16° for flat K orientation); however, the group mean variability was significantly higher in DS eyes than control eyes for all parameters (p ⩽ 0.03). On average, group mean variability was 2.5 times greater in the DS eyes compared to control eyes across the keratometry values. Other metrics of repeatability also indicated good repeatability for both populations for each keratometry value, although repeatability was always better in the control eyes. Conclusions DS eyes showed more variability (on average: 2.5×) compared to controls for all keratometry values. Although differences were statistically significant, on average 91% of DS eyes had variability ⩽0.50D for steep K and astigmatism, and 75% of DS eyes had variability ⩽5 degrees for flat K orientation.

Registration tolerance of a custom correction to maintain visual acuity.

Purpose To present a predictive model of the registration tolerance for wavefront-guided correction to maintain acuity within fixed limits and demonstrate the potential utility using two typical keratoconic eyes. Methods Change in log visual Strehl was plotted as a function of translation error for a series of rotations of a wavefront-guided correction. Contour lines were added at &Dgr;log visual Strehl levels predicted to induce one- and two-line losses of logMAR visual acuity. The model was validated by regressing measured acuity loss from subjects viewing acuity charts that were degraded by the residual wavefront error resulting from the movement of wavefront-guided correction against the model’s predicted acuity. Results The model’s predicted change in acuity can be substituted for measured change in acuity (R2 = 0.91) within measurement error (±0.1 logMAR). Translation and/or rotation of a wavefront-guided correction induced asymmetric optical tolerance to movement. Induced errors depended on the wavefront error being corrected, the wavefront-guided correction design, and the amount of registration error. Conclusions Change in log visual Strehl can be used to determine the registration tolerance necessary to keep the variation in acuity within user-defined limits. This tolerance is unique for each wavefront error and wavefront-guided correction design.

Accommodative accuracy by retinoscopy versus autorefraction spherical equivalent or horizontal meridian power: Accommodative accuracy testing

To assess agreement between accommodative lag by monocular estimation method (MEM) retinoscopy and Nott retinoscopy compared to open‐field autorefraction using spherical equivalent versus power in the 180 meridian for both children and adults.

Variability in objective refraction for persons with down syndrome

PURPOSE Down syndrome (DS) is associated with ocular and cognitive sequelae, which both have the potential to influence clinical measures of refractive error. This study compares variability of autorefraction among subjects with and without DS. METHODS Grand Seiko autorefraction was performed on 139 subjects with DS (age: 8-55, mean: 25 ± 9 yrs) and 138 controls (age: 7-59, mean: 25 ± 10 yrs). Subjects with three refraction measures per eye (DS: 113, control: 136) were included for analysis. Each refraction was converted to power vector notation (M, J0, J45) and a difference in each component (ΔM, ΔJ0, ΔJ45) was calculated for each refraction pairing. From these quantities, average dioptric strength ((Equation is included in full-text article.): square root of the sum of the squares of M, J0, and J45) and average dioptric difference ((Equation is included in full-text article.): square root of the sum of the squares of ΔM, ΔJ0, and ΔJ45) were calculated. RESULTS The DS group exhibited a greater median (Equation is included in full-text article.)(1Q: 1.38D M: 2.38D 3Q: 3.41D) than control eyes (1Q: 0.47D M: 0.96D 3Q: 2.75D) (P < .001). Likewise, the DS group exhibited a greater median (Equation is included in full-text article.)in refraction (1Q: 0.27D M: 0.42D 3Q: 0.78D) than control eyes (1Q: 0.11D M: 0.15D 3Q: 0.23D) (P < .001) with 97.1% of control eyes exhibiting (Equation is included in full-text article.)≤0.50D, compared to 59.3% of DS eyes. An effect of (Equation is included in full-text article.)on (Equation is included in full-text article.)was not detected (P = .3009) nor was a significant interaction between (Equation is included in full-text article.)and group detected (P = .49). CONCLUSIONS In the current study, comparing three autorefraction readings, median total dioptric difference with autorefraction in DS was 2.8 times the levels observed in controls, indicating greater potential uncertainty in objective measures of refraction for this population. The analysis demonstrates that J45 is highly contributory to the observed variability.