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 7 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 RMS (p < 0.001) and higher-order RMS (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 higher-order RMS than the normal group (p = 0.41). Of the 14 eyes studied, 10 successfully reached the exit criteria, achieving residual higher-order root mean square wavefront error (HORMS) 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 KC 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.

It is well known that the wavefront error (WFE) of the eye varies from individual to individual, with pupil diameter and with age. Numerous studies have been proposed evaluating the relationship between visual acuity and WFE but all these studies were performed with either a fixed pupil diameter or natural pupil diameter. It is still not clear if metrics of image quality correlates well with visual acuity independent of pupil diameter. Here we investigated the correlation between the change in visual acuity and change in 30 image quality metrics for a range of optical quality typically established in normal eyes that varies both with age and pupil diameter. Visual acuity was recorded for four normal subjects using simulated blurred logMAR acuity charts generated from the point spread functions of different scaled WFEs for 6 different pupil diameters (2 to 7mm in 1mm 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 WFE’s and all pupil diameter. Multiple regression analysis did not significantly increase the R2. Simple metrics derived from wave front error could potentially act as an objective surrogate to visual acuity without the need for complex models.

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).

Purpose To determine the number of JND's of wavefront blur necessary to induce a one line loss of best corrected visual acuity (VA). Setting Visual Optics Institute, College of Optometry, University of Houston, Houston, Texas, USA. Methods The 3mm wavefront error of a well corrected average eye was scaled to yield 9 small steps of blur quantified in units of log Visual Strehl (log VS). For each level of log VS, 10 unique three line acuity charts were convolved with the resulting point spread functions. Using a temporal forced choice paradigm, subjects compared each test chart to a reference test chart indicating which chart was blurrier. The difference between 80% and 50% on the psychometric functions defined a JND. VA was measured for 6 log VS values. The number of JND's necessary to lose one line of acuity was defined as the change in log VS necessary to lose one line of acuity divided by the 1 JND in log VS. Results Linear regression revealed log VS = −2.98 * (logMAR acuity) - 0.31; R2 = 0.961. The average JND in log VS is 0.049 ±0.012 resulting in an average of 6.1 JND's per line of log MAR acuity. Conclusions The RIQ metric, log VS, is highly correlated with logMAR acuity. The 6 JND's in log VS before 1 line of acuity is lost may provide an objective explanation for the distinction between “20/20 happy” and “20/20 unhappy” and other aberration related clinical complaints when acuity is near normal.