Introduction
As corneal ectasias progress in severity, the range of viable ophthalmic correction modalities decreases, and visual symptoms are most successfully alleviated using rigid contact lenses. Conventional (spherocylindrical) scleral lenses are gaining popularity due to superior comfort as well as improved visual quality resulting from targeting lower-order (spherocylindrical) aberrations and masking 60 to 70% of higher-order aberrations.1 Despite these improvements in optical quality, residual higher-order aberrations often remain statistically elevated1-3 relative to typical levels4 – even while wearing best conventional standard-of-care scleral lenses – and can lead to decreased visual performance and/or patient dissatisfaction. When clinicians exhausted conventional correction modalities, patients with severe ectasia were faced with the difficult choice between remaining dissatisfied with poor visual performance or undergoing invasive surgical interventions. Modern technology now offers another option, namely, wavefront-guided (WFG) corrections.
Wavefront-guided scleral lenses target lower- and higher-order aberrations that remain uncorrected through best conventional lenses. These WFG corrections have been successfully demonstrated in laboratory settings2,3 and translated into the daily lives of individuals with corneal ectasias.1 Wavefront-guided lenses are manufactured by multiple surfacing laboratories and are fit by a number of research groups as well as private practitioners. Being customized to the measured aberrations of individual eyes, WFG corrections are the ophthalmic reification of personalized medicine.
This report describes a case of severe keratoconus that was referred for penetrating keratoplasty because visual quality expectations were unsatisfied, and no further improvement could be made using conventional corrections. Such situations occur in keratoconus, where dissonance has been documented5 between visual expectations of the patient and the ability of spherocylindrical lenses to satisfy those expectations. Ultimately, using a WFG scleral lens, the visual goals of this individual were subjectively satisfied, and visual performance reached typical clinical benchmark levels. At a follow-up visit six months after the initial dispensing, those objective and subjective requirements were still being satisfied.
CASE REPORT
A 33-year-old male presented to the Visual Optics Institute at the University of Houston College of Optometry, dissatisfied with the best corrected visual quality in his left eye. He had been deemed ineligible for corneal crosslinking and intrastromal ring implants and had been referred for penetrating keratoplasty due to no improvement being possible to his habitual spherocylindrical scleral lens. Corneal topography (Pentacam HR, Oculus Inc., Arlington WA) confirmed bilateral, asymmetric, severe keratoconus (see Supplementary Materials for curvature, thickness, and elevation maps). Disease severity6 and steepest keratometry (Kmax) are quantified in Table 1.
Table 1.
Summary of diagnostic and performance data across four conditions: unaided, as well as aided with a habitual scleral lens, new spherocylindrical (SCA) scleral lens, and wavefront-guided (WFG) scleral lens. Severity7 of ectasia based on A: anterior corneal radius of curvature (mm), B: posterior corneal radius of curvature (mm), C: thinnest pachymetry (μm). Visual acuity is the mean of three unique ETDRS logMAR charts, using per-letter scoring, a termination rule of five incorrect. Higher-order (HO) root mean square (RMS) wavefront error (WFE) (μm) and the common (base-10) logarithm of the visual Strehl ratio9 (logVSX) are calculated over a 5-mm pupil diameter. Typical eye norms for HO RMS WFE5 and letter contrast sensitivity are appended for comparison.
| Unaided | Habitual scleral |
SCA scleral |
WFG scleral |
Six month follow up |
||
|---|---|---|---|---|---|---|
| Left eye | ||||||
| Disease severity: grading 7 | A | 4 (4.34) | ||||
| B | 4 (3.17) | |||||
| C | 3 (332) | |||||
| Steepest keratometry (Kmax) (D) | 84.7 | |||||
| Visual acuity | logMAR ±SD |
+0.20 ±0.06 | +0.06 ±0.04 | −0.05 ±0.01 | −0.03 | |
| Snellen | 6/9 | 6/7.5+2 | 6/6+2 | 6/6+1 | ||
| HO RMS WFE | 8.551 | 1.159 | 1.154 | 0.437 | 0.498 | |
| Letter contrast sensitivity ±SD | 4 cpd | 1.07 ±0.02 | 1.29 ±0.05 | 1.56 ±0.06 | ||
| 8 cpd | 0.74 ±0.05 | 1.06 ±0.05 | 1.30 ±0.09 | |||
| 16 cpd | 0.32 ±0.08 | 0.67 ±0.06 | 0.85 ±0.06 | |||
| logVSX | less negative is better | −1.627 | −1.618 | −0.727 | ||
| Typical eye norms | ||||||
| HO RMS WFE ±SD | 30-39 y/o 5 | 0.174 ±0.062 | ||||
| Letter contrast sensitivity ±SD | 4 cpd | 1.65 ±0.12 | ||||
| 8 cpd | 1.45 ±0.13 | |||||
| 16 cpd | 1.18 ±0.16 |
Residual wavefront aberrations (Figure 1) were measured (COAS HD, Johnson and Johnson Vision, Santa Ana, CA) while wearing the habitual scleral lens. Although higher-order root mean square (RMS) wavefront error was reduced by 86% from unaided, the residual (14% uncorrected) aberrations were more than six times the age-matched levels of typical eyes at the same pupil diameter (5 mm) and well outside the 95% normative range.4 Aided logMAR visual acuity was poor +0.20 (6/9 Snellen) (mean of three unique ETDRS charts; per-letter scoring; termination after five letters incorrect). Letter contrast sensitivity (mean of three measures) was outside the 95% range of typical control eyes on the same system (Cambridge Research Systems, Kent, UK) for 4, 8, and 16 cycles per degree fundamental spatial frequencies (Table 1), and the patient complained of halos and starbursts (see point spread function in Figure 1).
Figure 1.
Total wavefront error (μm) and simulated retinal images of four conditions for the left eye of a 33 year old with severe keratoconus. Retinal point spread functions and simulated retinal images are generated in the patient’s perceptual point of view rather than from the clinician perspective. Snellen equivalents of the logMAR letter sizes are: 0.5 = 6/18, 0.4 = 6/15, 0.3 = 6/12, 0.2 = 6/9. Horizontal and vertical extents of the inset point spread function boxes are 50 minutes of arc.
Prior to designing a WFG lens, a new spherocylindrical scleral lens was manufactured1,3 in Boston XO material (hexafocon A; Dk = 100; Bausch and Lomb, Rochester, NY). Although minor improvements to optical and visual performance were achieved by refining this new spherocylindrical lens (Table 1, Figure 1), the overall clinical evaluation agreed with the previous practitioner in that no substantial improvement was made to the habitual correction, and optical quality and visual performance remained noticeably inferior to the fellow eye and markedly worse than normal.
Wavefront error measured through the best conventional lens was used to design an individualized WFG scleral lens that targeted residual aberrations in the 2nd to 5th Zernike radial orders. The WFG lens followed the macro designs of the best conventional lens: same material, 18.1 mm total diameter, −12 D base sphere power, 10 mm back optic zone diameter, and six posterior surface curves. Tolerance for lens movement is inversely proportional to the magnitude of the wavefront-guided correction; the high levels of aberrations in this case required accurate lens stabilization on-eye (both translation and rotation) which was accomplished using a toric peripheral annulus in the fifth concentric zone.1,3 The orientation of this toric peripheral annulus was adjusted to compensate for the rotation component of the settled lens position.1,3 Additionally, the WFG optical correction was offset7 from the geometric lens center by −0.4507 mm horizontally (nasally) and +0.6550 mm vertically (superiorly) to position the correction over the pupil center by compensating for the measured inferior-temporal settling of the scleral lens on-eye. These offsets were calculated from high resolution photographs of reference engravings on the lens surface (see Supplementary Material).1,3
Higher-order aberrations residual through the WFG lens were 94% less than unaided and 60% less than those residual through the best conventional and habitual scleral lenses (Table 1). Visual acuity and letter contrast sensitivity improved substantially to within typical levels, and visual image quality – quantified by logVSX (base-10 logarithm of the visual Strehl ratio8) – increased by almost a log unit with the WFG lens (Table 1). The patient reported reduced halos and scatter and described the subjective visual quality as superior to that provided by other corrections. Patient care was transferred to the University Eye Institute (clinic).
At a follow-up six months after dispensing, the WFG lens provided a similar level of higher-order aberration correction (residual RMS 0.498 μm; 94% less than unaided) – this agreed with lens durability expectations.9 Corrected visual acuity remained within typical levels; letter contrast sensitivity was not measured in clinic. The patient reported continued satisfaction in subjective visual quality and referral for penetrating keratoplasty remained unnecessary.
DISCUSSION
This report describes a patient that was failed by the prevailing standard of care after exhausting the full range of conventional clinical corrections. This case also illustrates a dissonance5 between the expectations of patients and clinicians: Although the clinicians achieved a well-fit spherocylindrical scleral lens that substantially reduced aberrations (from unaided), these improvements nonetheless left the patient far from typical levels of visual performance and still generally dissatisfied with the quality of vision. Part of this dissonance stems from insensitivity of high contrast visual acuity to capture visual quality. Because more than six just-noticeable-differences in blur can be perceived before one line of visual acuity is lost,10 individuals with keratoconus might achieve nearly typical levels of visual acuity, despite poor subjective visual quality that does not meet their needs.
Rather than having to consider invasive ocular surgery at a young age, this case demonstrates how visual performance can be recovered in severe ectasia by using WFG corrections. Because keratoconus onset is usually during adolescence,6 these individuals experience typical visual stimulation during the sensitive and critical periods of neural development. Hence, correcting the acquired optical consequences (higher-order aberrations) of the disease should facilitate visual performance returning to typical levels.
Naturally, these performance gains come at a cost; both time and financial investments are required from the patient and clinician. While the physical integrity of a WFG correction remains intact over time,9 clinicians should consider the rate of disease progression when advocating for this technology. Here, the patient was willing and able to invest the time, and disease progression was sufficiently stable such that typical levels of visual performance were maintained. Small changes in higher-order aberrations at the follow-up (clinic) visit might be due to the lens resting at a different position or orientation to the measurements at the dispensing (laboratory) visit, or due to subtle disease progression.
Most contact lens clinicians already possess a high resolution means of photographing a lens on an eye that should suffice for quantifying lens position (see Supplementary Material). The additional instrument required for WFG corrections is a wavefront sensor that aligns with the line of sight of the eye – these instruments are increasingly commonplace and inexpensive. Moreover, specialty contact lenses are frequently motivated by optical challenges, and by providing comprehensive descriptions of ocular optics, wavefront sensors afford clinicians unrivaled perspectives into the experiences of patients (see the simulated retinal images in Figure 1). Most complexity in fitting a WFG lens involves obtaining a healthy and stable conventional scleral lens fit. Thereafter, the addition of the WFG correction is relatively straightforward,1-3 provided that a good quality wavefront error measurement can be obtained. In eyes with significant corneal opacification or scarring, obtaining high integrity wavefront error measurements can be challenging.
Wavefront-guided lens technology is no longer confined to research laboratories – patients are thriving with these lenses in their everyday lives. The only patients that should choose between living with poor visual quality or submitting to invasive corneal surgery are those clinically ineligible for scleral lenses. This case exemplifies how some individuals remain underserved by typical standards of clinical care and illustrates how clinicians can transform the existence of these individuals using modern individualized technology.
Supplementary Material
Figure S1. Slitlamp photographs of the wavefront-guided lens on the eye showing engravings on the anterior lens surface used to evaluate lens rotation and translation.
Figure S2. Corneal topography (curvature, elevation, and thickness) maps from the Pentacam HR (Oculus Inc., Arlington WA).
Figure S3. Second-order and higher-order (third through fifth orders) Zernike aberration coefficients for the four conditions described in this case (unaided, habitual scleral lens, new conventional (spherocylindrical) scleral lens, and wavefront-guided scleral lens).
ACKNOWLEDGEMENTS
National Eye Institute R01EY019105 (JDM and RAA), P30EY07551 (core grant to UH). The authors thank Katrina Parker for clinical assistance, Hope Queener for software support, and Sarver and Associates (Cookeville, TN) for the use of Visual Optics Laboratory software. The University of Houston holds patent interests on wavefront-guided corrections on which JDM and RAA are listed as inventors.
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Associated Data
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Supplementary Materials
Figure S1. Slitlamp photographs of the wavefront-guided lens on the eye showing engravings on the anterior lens surface used to evaluate lens rotation and translation.
Figure S2. Corneal topography (curvature, elevation, and thickness) maps from the Pentacam HR (Oculus Inc., Arlington WA).
Figure S3. Second-order and higher-order (third through fifth orders) Zernike aberration coefficients for the four conditions described in this case (unaided, habitual scleral lens, new conventional (spherocylindrical) scleral lens, and wavefront-guided scleral lens).