Utilising a visual image quality metric to optimise spectacle prescriptions for eyes with keratoconus.

PURPOSE: To compare optical performance, visual performance, and patient-perceived quality of vision with: (1) spectacles determined using subjective refraction and (2) spectacles determined using an objective optimisation method based on wavefront aberration data for eyes with keratoconus. METHODS: Thirty-seven eyes (20 subjects) with keratoconus underwent both subjective refraction and uncorrected wavefront aberration measurement. Wavefront aberration data were used to objectively identify a sphero-cylindrical refraction that optimised the visual image quality metric visual Strehl ratio (VSX). The two refractions were assembled in trial frames and worn by the subject in a random order. High-contrast visual acuity (VA), letter contrast sensitivity (CS), and the patient's short-term subjective preference were recorded for each prescription. RESULTS: Median magnitude of the dioptric difference (a measure of similarity between the subjective and objective refractions) was 2.77 D (range = 0.21-20.44 D, first quartile = 1.02 D, third quartile = 4.36 D). Sixty-eight per cent of eyes had better VA with the objective refraction and 32% of eyes gained more than one line of VA. Monocularly, objective refraction was preferred 68% of the time when looking at a distant acuity chart and 76% of the time when viewing a real-world dynamic scene. CONCLUSIONS: Objective refraction based on visual image quality derived from wavefront aberration data can be valuable in the determination of monocular spectacle refractions for individuals with keratoconus.

Case Report: When Two Is Worse Than One-Stereo Imbalance in a Case of Wavefront-guided Scleral Lenses.

SIGNIFICANCE: Wavefront-guided scleral lenses (WGSLs) reduce visually debilitating residual higher-order aberrations. Although reduced higher-order aberrations lead to improvement in monocular high-contrast visual acuity (VA), the success of the lenses in everyday life depends on additional factors such as retinal contrast, binocular balance, and stereoacuity. PURPOSE: This report describes a case where WGSLs provided improved monocular vision compared with scleral lenses (SLs) but reduced binocularity and stereoacuity. CASE REPORT: A 48-year-old woman with moderate keratoconus right eye (OD) and severe left eye (OS) was fitted with SLs and WGSLs. Visual acuity with best SLs was 20/20 -2 OD and 20/25 -2 OS. Residual higher-order root-mean-square (HORMS) wavefront error (6 mm pupil) was 0.56 µm OD and 1.38 µm OS. Visual acuity with WGSLs was 20/16 -2 OD and 20/25 +2 OS, and residual HORMS was 0.41 µm OD and 0.98 µm OS. Monocularly, WGSLs were reported to provide better VA. However, binocularly, the patient reported an "imbalanced feeling" and preferred the SLs over WGSLs. Binocular VA at distance was 20/25 with SLs and 20/25 -2 with WGSL. To investigate, the Worth Four-Dot test was performed, and the outcomes reported fusion with SLs but suppression OS at distance with WGSLs. Stereoacuity was 160 arc seconds at near and 120 arc seconds at distance with SLs and 400 arc seconds at near and >1200 arc seconds at distance with WGSLs. Dichoptic contrast balancing showed a balance point of 0.48 with SLs and 0.17 with WGSLs, indicating a strong preference toward OD. Simulation of the patient's retinal image revealed a greater difference in image contrast between the two eyes with WGSLs. CONCLUSIONS: Wavefront-guided scleral lenses reduced HORMS and improved VA compared with SLs. However, in this case, it inadvertently caused binocular imbalance. As WGSLs become more widely available, future work should include methods to optimize binocular balance to maximize overall patient satisfaction.

Quantifying the Optical and Physical Consequences of Daily Cleaning on Conventional and Wavefront-guided Scleral Lenses.

SIGNIFICANCE: An equivalent 12 months of cleaning did not induce significant changes in the optical aberrations or base curves of scleral lenses. PURPOSE: This study aimed to test whether an equivalent of 12 months of manual cleaning alters the optical and physical properties of conventional and wavefront-guided scleral lenses. METHODS: Twelve scleral lenses (four repeats of three designs, termed A, B, and C) were manufactured in Boston XO material: design A, -5.00 D defocus; design B, -5.00 D defocus with -0.153-µm vertical coma; and design C, -5.00 D defocus with a full custom wavefront-guided correction (second to fifth Zernike radial orders) of an eye with severe keratoconus. One lens of each design group served as a control and was not cleaned. To simulate a year of cleaning, seven individuals cleaned nine lenses (three from each group) twice a day for 27 days using the palm technique and commercially available cleaners, resulting in 378 cleanings of each lens. Lens aberrations were optically profiled and base curve radii were measured at baseline and after every 42nd cleaning. Differences in higher-order root mean square (HORMS) wavefront error and base curve radii associated with cleaning were compared with clinical benchmarks and using sign tests. RESULTS: For the experimental lenses, median change in Seidel spherical dioptric power was +0.01 D (maximum, +0.025 D). Median change in HORMS wavefront error was 0.013 µm (maximum, 0.019 µm). All lenses exhibited HORMS changes less than one-eighth equivalent diopters (P = .002). Median percentage change in HORMS wavefront error in the three wavefront-guided lenses was 0.96% (maximum, 1.25%). Median change in base curve radii was 0.00 mm, with all lenses exhibiting changes (P = .002), less than the American National Standards Institute tolerance of 0.05 mm. CONCLUSIONS: Cleaning over an equivalent 12-month period did not induce clinically significant changes in the optical or base curve properties of conventional or wavefront-guided scleral lenses.

Case Report: What Are We Doing for Our "20/20 Unhappy" Scleral Lens Patients?

SIGNIFICANCE: Scleral lenses (SLs) partially mask higher-order aberrations (HOAs) in highly aberrated eyes. Although visual acuity (VA) may show satisfactory quantitative clinical outcomes during SL wear, residual (uncorrected) HOAs can leave subjective visual quality goals unmet. PURPOSE: The purpose of this study was to report a case where a "20/20 unhappy" patient with SLs was able to meet visual goals with wavefront-guided SLs. CASE REPORT: A 40-year-old male with bilateral keratoconus, whose Snellen VA with SLs was 20/20 right eye (OD) 20/16 left eye (OS), reported halos and glare at night and perceptual smearing. When viewing a point of light, a "Ferris wheel" shadowing was observed OD and a U-shaped shadowing OS. Residual higher-order root mean square wavefront error was 0.49 µm OD and 0.39 µm OS; visual image quality measured by visual Strehl ratio was 0.067 OD and 0.092 OS (pupil size, 4.00 mm). Wavefront-guided SLs reduced residual higher-order root mean square to 0.19 µm OD and 0.25 µm OS, VA improved to 20/10 OD and 20/13 OS, and visual Strehl improved to 0.150 OD and 0.121 OS. The patient reported reduced smearing, shadowing, and night vision concerns, meeting his visual expectations and goals. CONCLUSIONS: Wavefront sensing quantifies both lower and HOAs, which can cause visual dissatisfaction in individuals with highly aberrated eyes, despite sometimes reaching typical levels of VA. As wavefront-guided SLs targeting these residual aberrations to improve visual image quality become more available, they should be considered for 20/20 unhappy patients when conventional clinical options are unsatisfactory.

The Impact of Misaligned Wavefront-guided Correction in a Scleral Lens for the Highly Aberrated Eye.

SIGNIFICANCE: To achieve maximum visual benefit, wavefront-guided scleral lens corrections (WGCs) are aligned with the underlying wavefront error of each individual eye. This requirement adds complexity to the fitting process. With a view toward simplification in lens fitting, this study quantified the consequences of placing WGCs at two pre-defined locations. PURPOSE: This study aimed to quantify performance reduction accompanying the placement of the WGC at two locations: (1) the average decentered location (ADL; average decentration observed across individuals wearing scleral lenses) and (2) the geometric center (GC) of the lens. METHODS: Deidentified residual aberration and lens translation data from 36 conventional scleral lens-wearing eyes with corneal ectasia were used to simulate WGC correction in silico. The WGCs were decentered from the eye-specific pupil position to both the ADL and GC locations. The impact of these misalignments was assessed in terms of change (from the aligned, eye-specific pupil position) in higher-order root mean square (HORMS) wavefront error, change in log of the visual Strehl ratio (logVSX), and predicted change in logMAR visual acuity (VA). RESULTS: As expected, HORMS increased, logVSX decreased, and predicted VA was poorer at both ADL and GC compared with the aligned condition (P < .001). Thirty-four of 36 eyes had greater residual HORMS, and 33 of 36 eyes had worse logVSX values at the GC than at the ADL. In clinical terms, 19 of 36 eyes at the ADL and 35 of 36 eyes at the GC had a predicted loss in VA of three letters or greater. CONCLUSIONS: The placement of the WGC at either ADL or GC is predicted to lead to a noticeable reduction in VA for more than half of the eyes studied, suggesting the simplification of the fitting process is not worth the cost in performance.

Alignment of a wavefront-guided scleral lens correction in the presence of a lens capsulotomy.

PURPOSE: To demonstrate the necessity of aligning a wavefront-guided scleral lens (WGSL) optical correction to the eye's effective pupil, with misalignments leading to reduced performance. CASE REPORT: A 34 year old subject with a history of failed LASIK in the left eye, leading to penetrating keratoplasty, extracapsular extraction of the crystalline lens and neodymium:yttrium-aluminum-garnet (Nd:YAG) laser posterior capsulotomy, enrolled in a study examining WGSL performance. Habitual logMAR acuity OS (aided with a scleral lens) was +0.04. Residual higher order root mean square (HORMS) wavefront error (WFE) was 0.28 µm (Φ =4.75 mm, mean age-matched norm =0.17 µm), and objective over-refraction was -0.30 -0.54 × 008. When a WGSL (targeting aberrations up to the 5 th radial order) was manufactured with the wavefront-guided optics aligned to the center of the dilated pupil, logMAR acuity worsened to +0.15, residual HORMS WFE worsened to 0.44 µm (Φ =4.75 mm), and objective over-refraction increased to +1.19 -0.30 × 122. Slit lamp imagery revealed that the effective pupil was no longer defined by the iris of the eye, but rather the capsular opening created by the capsulotomy. When the WGSL was redesigned to align the wavefront-guided optics to the center of the capsular opening, logMAR acuity improved to -0.14, residual HORMS WFE reduced to 0.17 µm (Φ =4.75 mm) and objective over-refraction reduced to +0.20 -0.15 × 111. CONCLUSION: WGSLs are an emerging option for patients with highly aberrated, ectatic and post-surgical corneas whose visual symptoms cannot be alleviated with conventional corrections. However, alignment of the optics of the WGSL to the underlying optics of the eye over the effective pupil is critical in achieving good optical and visual performance.

Acquisition of Plasmid with Carbapenem-Resistance Gene blaKPC2 in Hypervirulent Klebsiella pneumoniae, Singapore.

The convergence of carbapenem-resistance and hypervirulence genes in Klebsiella pneumoniae has led to the emergence of highly drug-resistant superbugs capable of causing invasive disease. We analyzed 556 carbapenem-resistant K. pneumoniae isolates from patients in Singapore hospitals during 2010-2015 and discovered 18 isolates from 7 patients also harbored hypervirulence features. All isolates contained a closely related plasmid (pKPC2) harboring blaKPC-2, a K. pneumoniae carbapenemase gene, and had a hypervirulent background of capsular serotypes K1, K2, and K20. In total, 5 of 7 first patient isolates were hypermucoviscous, and 6 were virulent in mice. The pKPC2 was highly transmissible and remarkably stable, maintained in bacteria within a patient with few changes for months in the absence of antimicrobial drug selection pressure. Intrapatient isolates were also able to acquire additional antimicrobial drug resistance genes when inside human bodies. Our results highlight the potential spread of carbapenem-resistant hypervirulent K. pneumoniae in Singapore.

Do Polymer Coatings Change the Aberrations of Conventional and Wavefront-guided Scleral Lenses?

SIGNIFICANCE: The findings of this study indicate that patients could simultaneously be offered the individualized optical correction of wavefront-guided (WFG) lenses and the superior comfort afforded by polymer coatings. This could be helpful to patients with ectasia suffering ocular dryness or dependent on scleral lenses for lengthy periods of wear. PURPOSE: Wavefront-guided scleral lenses target lower- and higher-order aberrations of individual eyes using submicrometer-level contours in the anterior lens surface. Hydrophilic polyethylene glycol (PEG) polymer coatings applied to lens surfaces improve comfort and wettability. This study aimed to quantify aberration changes (e.g., masking) when applying polymer coatings to WFG and conventional scleral lenses. METHODS: Two control lenses (remained uncoated) and 14 experimental lenses (two repeated builds of seven aberration designs: one spherical, two coma, four full WFG [second- to fifth-order aberrations]) were manufactured, and aberrations were measured (mean of three) by two operators before and after coating. Root mean square (RMS) and visual image quality (logVSX) differences were calculated for 6-mm diameters. RESULTS: Median RMS aberration change due to coating was 0.012 µm (range, 0.008 to 0.057 µm). Maximum logVSX change due to coating was 0.073, predicting an approximately one letter change in acuity. Instrument sensitivity was 0.002 µm. Acute instrument and operator variabilities (standard deviations of individual [second- to fifth-order Zernikes] were all <0.027 µm). Longitudinal variability (control lenses) was low: all less than 0.017 µm. Although RMS of differences between repeated builds of all lenses was less than 0.25 D and not statistically significant, relatively, manufacture constituted the major variability, and RMS difference between repeated builds was at least four times greater than the effect of coating (median, 0.167 µm; range, 0.088 to 0.312 µm). CONCLUSIONS: Application of polymer coatings caused measurable changes in aberrations of WFG and conventional scleral lenses; however, these were clinically and statistically insignificant and within variability of repeated lens manufacture. In their current states, WFG lenses and polymer coatings could be used simultaneously.

Comparison of Wavefront-guided and Best Conventional Scleral Lenses after Habituation in Eyes with Corneal Ectasia.

SIGNIFICANCE: Visual performance with wavefront-guided (WFG) contact lenses has only been reported immediately after manufacture without time for habituation, and comparison has only been made with clinically unrefined predicate conventional lenses. We present comparisons of habitual corrections, best conventional scleral lenses, and WFG scleral lenses after habituation to all corrections. PURPOSE: The purpose of this study was to compare, in a crossover design, optical and visual performance of eyes with corneal ectasias wearing dispensed best conventional scleral lens corrections and dispensed individualized WFG scleral lens corrections. METHODS: Ten subjects (20 eyes) participated in a randomized crossover study where best conventional scleral lenses and WFG scleral lenses (customized through the fifth radial order) were worn for 8 weeks each. These corrections, as well as each subject's habitual correction and normative data for normal eyes, were compared using (1) residual higher-order aberrations (HORMS), (2) visual acuity (VA), (3) letter contrast sensitivity (CS), and (4) visual image quality (logarithm of the visual Strehl ratio, or logVSX). Correlations were performed between Pentacam biometric measures and gains provided by WFG lenses. RESULTS: Mean HORMS was reduced by 48% from habitual to conventional and 43% from conventional to WFG. Mean logMAR VA improved from habitual (+0.12) to conventional (-0.03) and further with WFG (-0.09); six eyes gained greater than one line with WFG over conventional. Area under the CS curve improved by 26% from habitual to conventional and 14% from conventional to WFG. The percentage of the eyes achieving normal levels were as follows: HORMS, 40% for conventional and 85% for WFG; VA, 50% for conventional and 85% for WFG; and CS, 60% for conventional and 90% for WFG. logVSX improved by 16% from habitual to conventional and 25% further with WFG. Reduction in aberrations with WFG lenses best correlated with posterior cornea radius of curvature. CONCLUSIONS: Visual performance was superior to that reported with nonhabituated WFG lens wear. With WFG lenses, HORMS and logVSX significantly improved, allowing more eyes to reach normal levels of optical and visual performance compared with conventional lenses.

Is an objective refraction optimised using the visual Strehl ratio better than a subjective refraction?

PURPOSE: To prospectively examine whether using the visual image quality metric, visual Strehl (VSX), to optimise objective refraction from wavefront error measurements can provide equivalent or better visual performance than subjective refraction and which refraction is preferred in free viewing. METHODS: Subjective refractions and wavefront aberrations were measured on 40 visually-normal eyes of 20 subjects, through natural and dilated pupils. For each eye a sphere, cylinder, and axis prescription was also objectively determined that optimised visual image quality (VSX) for the measured wavefront error. High contrast (HC) and low contrast (LC) logMAR visual acuity (VA) and short-term monocular distance vision preference were recorded and compared between the VSX-objective and subjective prescriptions both undilated and dilated. RESULTS: For 36 myopic eyes, clinically equivalent (and not statistically different) HC VA was provided with both the objective and subjective refractions (undilated mean ± S.D. was -0.06 ± 0.04 with both refractions; dilated was -0.05 ± 0.04 with the objective, and -0.05 ± 0.05 with the subjective refraction). LC logMAR VA provided by the objective refraction was also clinically equivalent and not statistically different to that provided by the subjective refraction through both natural and dilated pupils for myopic eyes. In free viewing the objective prescription was preferred over the subjective by 72% of myopic eyes when not dilated. For four habitually undercorrected high hyperopic eyes, the VSX-objective refraction was more positive in spherical power and VA poorer than with the subjective refraction. CONCLUSIONS: A method of simultaneously optimising sphere, cylinder, and axis from wavefront error measurements, using the visual image quality metric VSX, is described. In myopic subjects, visual performance, as measured by HC and LC VA, with this VSX-objective refraction was found equivalent to that provided by subjective refraction, and was typically preferred over subjective refraction. Subjective refraction was preferred by habitually undercorrected hyperopic eyes.

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.

Factors accounting for the 4-year change in acuity in patients between 50 and 80 years.

PURPOSE: It is well known that acuity slowly decreases in the later decades of life. We wish to determine the extent by which 4-year longitudinal acuity changes can be accounted for by changes in optical quality, or combination of optical quality metrics and of age between 50 and 80 years. METHODS: High-contrast logMAR acuity, 35 image quality metrics, 4 intraocular scatter metrics, and 4 Lens Opacification Classification System III metrics and entry age were measured on one eye of each of the 148 subjects. Acuity change between baseline and the last visit was regressed against change in each metric for all eyes and a faster changing subset of 50 eyes with a gain or loss of four or more letters. RESULTS: Average change across 148 subjects was a 1.6 ± 4 letter loss (t148 = 4.31, p < 0.001) and loss for the faster changing subset was 3.4 ± 6.1 letters (t50 = 2.73, p = 0.008). The multiple-regression model for faster changing eyes included change in point spread function entropy, posterior subcapsular cataract, and trefoil and baseline age (sequential r adjusted values of 0.19, 0.27, 0.32, and 0.34, respectively; p = 1.48 × 10 for the full four-factor model). The same variables entered the multiple-regression model for the full 148 data set where most of the acuity measurements were within test-retest error and accounted for less of the variance (r adjusted = 0.15, p = 2.37 × 10). CONCLUSIONS: Despite being near noise levels for the measurement of acuity, change in optical quality metrics was the most important factor in eyes that lost or gained four or more letters of acuity. These findings should be generalizable given that our 4-year acuity change is essentially identical to other studies and indicate that these optical quality markers can be used to help identify those on a faster track to an acuity change.

Detecting significant change in wavefront error: how long does it take?

PURPOSE: Measurement noise in ocular wavefront sensing limits detection of statistically significant change in high-order wavefront error (HO WFE). Consequently, measurement noise is problematic when trying to detect progressive change in HO WFE. Our aims were to determine the necessary amount of time to detect age-related change in HO WFE given measurement variability and HO WFE composition and magnitude; and to minimise the length of time necessary to detect change. METHODS: Five subjects with 0.26 to 1.57 micrometres root mean square HO WFE (HORMS) over a 6 mm pupil were measured 12 times in 10 to 15 minutes using a custom Shack-Hartmann wavefront sensor. Each individual's standard deviation of measures was used to calculate the 95% confidence interval around their mean HO RMS. Data previously reported on the rate of change in the HO RMS due to normal ageing and pupil diameter were used to calculate time to detect change exceeding this interval given measurement variability. RESULTS: Single measurements limit statistical detection to a range of eight to 30 years.Increasing the number of WFE measurements per visit decreases time to detection (for example, seven measurements reduce the range to three to 14 years). The number of years to detect a change requires consideration of the subject's measurement variability,level and distribution of aberrations and age. Uncertainty in locating pupil centre accounts for 39 +/- 8 per cent of the total variability. CONCLUSIONS: The ability to detect change in HO WFE over a short period due to normal ageing is difficult but possible with current WFE measurement technology. Single measurements of HO WFE become less predictive of true HO WFE with increasing measurement variability. Multiple measurements reduce the variability. Even with proper fixation and instrument alignment, pupil centre location uncertainty in HO WFE measurements is a non-trivial contributor to measurement variability.