Katrina E. Parker

Performance of wavefront-guided soft lenses in three keratoconus subjects

Purpose. To examine whether custom wavefront-guided soft contact lenses provide visual and optical performance equivalent to habitual gas permeable (GP) corrections in three keratoconus subjects. Methods. Custom wavefront-guided soft contact lenses were produced and evaluated at the Visual Optics Institute, College of Optometry, University of Houston for three habitual GP-wearing keratoconus subjects. Photopic high and mesopic low contrast logarithm of minimum angle of resolution visual acuity (logMAR VA) and residual second to tenth order optical aberrations experienced with these custom soft lenses were recorded and compared with the subjects’ habitual GP correction. Results. All three subjects wearing custom soft lenses reached the established exit criterion of photopic high contrast (HC) logMAR VA equal to or better than values recorded with their habitual GP lens. HC logMAR VA for GP and custom soft lens correction was 0.01 ± 0.05 and 0.00 ± 0.02 for KC1, 0.20 ± 0.02 and 0.14 ± 0.02 for KC2, and 0.04 ± 0.09 and −0.05 ± 0.05 for KC3, respectively. In addition, KC2 reached the exit criterion of high-order aberration levels equal to or less than values with their habitual GP lens (GP lens: 0.394 ± 0.024 &mgr;m, custom lens: 0.381 ± 0.074 &mgr;m). Conclusions. Custom wavefront-guided soft contact lenses have been demonstrated to provide equivalent photopic HC logMAR VA to that achieved with habitual GP correction in three keratoconus subjects. Future emphasis will be placed on surpassing habitual GP performance and reaching a normal age-matched criterion for both VA and aberration measures. Achieving these goals may require a more thorough understanding of the relationship between visual performance and residual aberration experienced during custom lens wear through the use of image quality metrics predictive of visual performance.

On-eye performance of custom wavefront-guided soft contact lenses in a habitual soft lens-wearing keratoconic patient

PURPOSE To assess visual, optical, and fitting characteristics for wavefront-guided soft contact lenses produced for one habitual soft lens-wearing moderate keratoconic eye. METHODS A process for production and evaluation of custom wavefront-guided soft contact lenses was developed. Wavefront aberrations were quantified with the COAS-HD wavefront sensor (Wavefront Sciences); soft contact lenses containing both high and low order aberrations were designed with custom software and produced using an ophthalmic lens lathe. Photopic high and low contrast logMAR visual acuity were recorded with the lens in place over an artificial 5-mm pupil and residual 2nd to 10th order root-mean-square (RMS) aberrations were analyzed over a 5-mm pupil. Comparisons were made to the eyes habitual toric soft contact lens using t tests. RESULTS Photopic high contrast values for habitual and final custom contact lenses for a 5-mm pupil were 0.07+/-0.06 and -0.08+/-0.05, respectively. Photopic low contrast values were 0.73+/-0.06 and 0.62+/-0.07, respectively. Habitual and final custom correction low order RMS over a 5-mm pupil were 2.08 and 0.34 microm, and high order RMS levels were 0.77 and 0.39 microm, respectively. CONCLUSIONS The final custom contact lens showed 1.5 lines of improvement for photopic high contrast (P=.03) and 1 line for photopic low contrast (P=.11) over a 5-mm pupil compared to habitual correction. Low and high order aberrations were reduced by 84% and 50% over a 5-mm pupil, respectively. Further improvements in performance of custom lenses may be achieved with further wavefront iterations.

Uncorrected Wavefront Error and Visual Performance During RGP Wear in Keratoconus

Purpose. To examine the relationship between uncorrected residual wavefront error and visual performance (VP) in rigid gas permeable (RGP) contact lens-wearing keratoconic eyes. Methods. Seven eyes from six subjects (six moderate, one severe) were studied (mean ± SD age: 42.71 ± 11.38 years). Significant corneal scarring was an exclusion criterion. Measurements were taken with RGP lenses in place. After pupil dilation, the VP measures of high contrast logMAR visual acuity (VA) and Pelli-Robson contrast sensitivity (PRCS) were measured through a 5-mm artificial pupil. Wavefront error was measured using a Shack–Hartmann wavefront sensor and calculated over 5 mm. For both VP and wavefront error, comparisons were made to previously collected normal values by calculating the interval encompassing 95% of normals, then reporting how many of the seven keratoconic eyes fell outside the normal interval. Additionally, second to sixth order aberrations were processed into four previously reported image quality metrics: root mean square of the wavefront (RMSw), root mean square of the slope (RMSs), average blur strength (Bave) and diameter containing 50% light energy (D50) and regressed against VP measures. Results. Five of seven keratoconic eyes fell outside the normal interval (−0.23 to 0.09) for VA and two of seven fell outside the normal interval (1.59 to 2.03) for PRCS. Five of seven keratoconic eyes fell outside the normal interval (0.07 to 0.35 &mgr;m) for total higher order RMS. Linear regressions demonstrated relationships between both VA and PRCS and the image quality metrics RMSw, D50, RMSs, and Bave with R2 values for VA = 0.30, 0.30, 0.47, 0.62, and PRCS = 0.21, 0.15, 0.45, 0.75 respectively. Conclusions. VP in RGP-wearing keratoconic eyes is reduced and higher order wavefront aberrations are elevated compared to normals. Metrics of retinal image quality demonstrate a relationship between keratoconic VP and residual wavefront aberrations. This relationship suggests developing corrections that more completely correct aberrations may improve visual performance in keratoconus.

The precision of wavefront refraction compared to subjective refraction and autorefraction.

Purpose. To determine the precision (repeatability) of several methods of calculating refraction from higher-order wavefront aberration data and to compare these wavefront refractions with lower-order (LO) wavefront refraction, subjective refraction, and autorefraction. Methods. Four clinicians refracted 16 normal participants aged 23.6 ± 1.2 years, 69% female with an average spherical equivalent refractive error of −3.03 ± 2.55 D, median sphere −2.50 D (minimum −7.50, maximum +4.75), and median cylinder −0.50 D (minimum −3.00, maximum 0). Participants were cyclopleged and underwent subjective refraction, autorefraction on two machines (Nidek AR-800, Topcon KR-8000), and wavefront sensing using the Wavefront Sciences Complete Ophthalmic Analysis System. Wavefront error was used to calculate: LO refraction, refractions that incorporated higher-order spherical and astigmatism terms from up to the 4th, 6th, and 10th orders (PCM4, PCM6, and PCM10), and a method based on optimizing image quality metrics [wavefront analysis technology (WAT) refraction]. Within and between examiner agreements for total dioptric difference were determined using Bland–Altman limits of agreement (LOA). Results. The interexaminer LOA for individual measurements for M, J0, J45 were: Topcon (±0.18, ±0.10, ±0.06), Nidek (±0.28, ±0.16, ±0.09), LO (±0.17, ±0.10, ±0.06), PCM4 (±0.26, ±0.09, ±0.06), PCM6 (±0.37, ±0.17, ±0.34), PCM10 (±0.54, ±0.32, ±0.40), WAT (±0.28, ±0.20, ±0.15), and subjective refraction (±0.48, ±0.20, ±0.13) and averaging across three measures LOA: Topcon (±0.15, ±0.08, ±0.05), Nidek (±0.21, ±0.13, ±0.07), LO (±0.12, ±0.06, ±0.04), PCM4 (±0.16, ±0.05, ±0.04), PCM6 (±0.23, ±0.09, ±0.19), PCM10 (±0.29, ±0.19, ±0.24), and WAT (±0.18, ±0.12, ±0.10). The within-examiner LOA for M, J0, J45 were: Topcon (±0.08, ±0.04, ±0.02), Nidek (±0.13, ±0.07, ±0.05 D), LO (±0.11, ±0.07, ±0.04), PCM4 (±0.17, ±0.07, ±0.04 D), PCM6 (±0.28, ±0.12, ±0.24 D), PCM10 (±0.42, ±0.24, ±0.32 D), and WAT (±0.19, ±0.14, ±0.09 D). Conclusions. All objective refractions except for PCM10 were more repeatable across clinicians than subjective refraction. The precision of all refractions were improved by an expected amount through averaging over multiple measurements. Wavefront refractions were not as precise as standard autorefractions, although not clinically significantly worse.

Empirical Advanced Orthokeratology Through Corneal Topography: The University of Houston Clinical Study

Purpose. Traditionally, orthokeratology has used diagnostic lenses to determine the best fit. The purpose of this study was to determine the efficacy of fitting empirically from corneal topography, without the use of diagnostic lenses. Methods. Twenty-nine subjects, 18 to 37 years old, with myopia of 1.00 to 4.00 diopters (D) and astigmatism of no more than 1.50 D, were entered into this 6-month study. Corneal topography, scanning slit topography and corneal thickness (Orbscan), confocal microscopy, ultrasound corneal thickness, aberrometry, and biomicroscopy were used to assess corneal changes. Unaided logMAR high-contrast visual acuity, subjective refraction, and questionnaires were used to monitor vision and symptoms. Follow-up visits were scheduled after 1 day, 1 week, 2 weeks, 1 month, 3 months, and 6 months. Results. For 6-month data, unaided logMAR acuity improved from 0.78 ± 0.26 in the right eye and 0.75 ± 0.22 in the left eye to 0.06 ± 0.18 in the right eye and 0.04 ± 0.16 in the left eye. Myopia decreased from –2.55 ± 0.87 D in the right eye and −2.47 ± 0.89 D in the left eye to +0.45 ± 0.74 D in the right eye and −0.17 ± 0.69 D in the left eye. Shape factor, using corneal topography, increased from 0.85 ± 0.13 in the right eye and 0.85 ± 0.15 in the left eye to 1.28 ± 0.32 in the right eye and 1.30 ± 0.29 in the left eye. Both eyes showed a decrease in lower-order aberrations (i.e., defocus) and an increase in higher-order aberrations (i.e., spherical aberrations and coma). Conclusions. Myopia reduction after 1 week was clinically insignificant from the 1-month results, indicating that the full effect is achieved by 1 week. Neither total nor epithelial corneal thickness varied significantly from baseline measurements.

Controlled induction of spherical aberration with custom soft contact lenses

Background:  This study investigated the non‐invasive induction of spherical aberration (SA) levels consistent with complication‐free wavefront‐guided (WFG) refractive surgery using custom WFG soft contact lenses and quantified the resulting impact on visual performance.

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 r2 adjusted values of 0.19, 0.27, 0.32, and 0.34, respectively; p = 1.48 × 10−4 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 (r2 adjusted = 0.15, p = 2.37 × 10−5). 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.

Orthokeratology: An Academic Perspective.

V arious methods of correcting and/or preventing myopia through manipulation of ocular structures and/or exercises have been reported over the last 300 years. With the introduction of PMMA corneal contact lenses, eye care practitioners began to notice that many young myopic contact lens wearers seemed to have some improvement in their vision, a reduction in their myopic progression, or both. In 1962, George Jessen became the first clinician to report on attempts to deliberately alter corneal curvature with PMMA contact lenses using his “orthofocus” techniques, which later became known as “orthokeratology.” In 1970, Grant and May reported on a fitting method using larger diameter lenses and maintaining the contact lens base curve at 0.12 D to 0.50 D flatter than the flat keratometry reading. Their techniques were emulated by other orthokeratologists for many years. Over the next 25 years, a multitude of reports on the results obtained through orthokeratology were published. Unfortunately, most of these “studies” were uncontrolled and anecdotal in nature with extremely variable results. There were four prospective investigations with some controls that were conducted from 1973 to 1984. Based on these studies, conventional orthokeratology fell into disfavor among most eye care practitioners and was declared not to be a viable option for the correction of myopia in the optometric and ophthalmological literature. It was during this period that most schools/colleges of optometry barely mentioned orthokeratology or did so in a negative way. Nevertheless, clinicians who advocated orthokeratology continued to refine the technique and improve lens designs until the first reverse geometry lens design in a high Dk material was introduced in 1989, creating a renewed interest among clinicians. However, it was not until 2002, when the first Food and Drug Administration (FDA) approval for overnight corneal reshaping was obtained by Paragon Vision Inc. (Mesa, Az) for its CRT lens design that the schools or colleges began to provide more instruction in this area. FDA approval of the B+L VST procedure for orthokeratology was also granted in 2004, which provided even more options to the practitioner. Over the last 10 to 12 years, there has been an increasing emphasis on understanding and preventing myopia progression, which has paralleled the development of orthokeratology. This is largely due to the increase in the prevalence of myopia in the United States from 25% (1971–1972) to 46% (1999–2004) and promising results in myopia research. Historically, management options have been limited as compared with the increasingly accepted forms of treatment today. Orthokeratology, soft multifocal contact lenses, and atropine therapy are currently an essential part of the clinician’s armamentarium for attempting to decrease myopic progression. So, how are future optometrists being educated on these options? What fitting modalities are being used in optometric education today? And is it enough?