Occlusion properties of prosthetic contact lenses for the treatment of amblyopia
Article Outline
Background
The efficacy of opaque contact lenses as occlusion therapy for amblyopia has been established in the literature. Prosthetic contact lenses use similar tints to improve cosmesis in scarred or deformed eyes and may be an alternative in occlusion therapy. To test this idea, we determined the degree of vision penalization elicited by prosthetic contact lenses and their effect on peripheral fusion.
Methods
We tested 19 CIBA Vision DuraSoft 3 Prosthetic soft contact lenses with varying iris prints, underprints, and opaque pupil sizes in 10 volunteers with best-corrected Snellen distance visual acuity of 20/20 or better in each eye. Snellen visual acuity and peripheral fusion using the Worth 4-Dot test at near were measured on each subject wearing each of the 19 lenses.
Results
Results were analyzed with 3-factor analysis of variance. Mean visual acuity through the various lenses ranged from 20/79 to 20/620. Eight lenses allowed preservation of peripheral fusion in 50% or more of the subjects tested. Iris print pattern and opaque pupil size were significant factors in determining visual acuity (p < 0.05).
Conclusions
Sufficient vision penalization can be achieved to make occlusion with prosthetic contact lenses a viable therapy for amblyopia. The degree of penalization can be varied and different iris print patterns and pupil sizes, using peripheral fusion, can be preserved with some lenses. Prosthetic contact lenses can be more cosmetically appealing and more tolerable than other amblyopia treatment modalities. These factors may improve compliance in occlusion therapy.
Amblyopia is defined as “poor vision caused by abnormal visual development secondary to abnormal visual stimulation.”1 Common causes include strabismus, anisometropia, and deprivation, resulting in aberrant development of cortical visual centers. It is the most common cause of decreased vision in children, with a prevalence of approximately 2% in the United States.2 Treatment involves occluding or penalizing the nonamblyopic eye. Patching provides inexpensive, complete occlusion and is immediately reversible with patch removal. However, compliance can be a problem with patching therapy. Bangerter foils can be applied to spectacles to penalize vision of the nonamblyopic eye to therapeutic levels. The degree of penalization can be adjusted to the needs of individual patients while maintaining peripheral fusion.3 However, children often peer around the lens with the applied foil. Other options include blurring the nonamblyopic eye with topical atropine or high-plus lenses. Atropine drops are tolerated by some children; however, the degree of penalization can be variable and it cannot be rapidly reversed. Potential side effects must also be considered. Recent research suggests there may be benefit to treating amblyopia in patients as old as 17 years of age, which may increase the motivation for practitioners to offer more appealing treatment options.4
Several studies have shown the efficacy of occlusive contact lenses for treatment of amblyopia. Eustis and Chamberlain5 found that vision improved by at least one line in 23 of 25 amblyopic children and that 14 of 17 patients who had failed conventional treatment (patching and/or atropine) showed improvement with occlusive contact lenses. Tsubora and Yamada6 found similar improvement in 8 of 9 patients who were managed with opaque, extended-wear contact lenses. Joslin et al7 also studied children who had failed patching therapy, and they also found varying levels of success. All reviewed literature suggests that occluder contact lenses are a viable alternative to patches and other forms of penalization therapy.
Prosthetic contact lenses are marketed by a number of manufacturers with designs intended to mask scars and disfigured eyes and to provide a more normal appearance.8 These lenses can be made with opaque prosthetic pupils by the same tinting processes as the occluder contact lenses previously studied. However, to our knowledge, no studies have yet been done to determine the degree of penalization that can be achieved with the various features available in prosthetic lenses. The objective of this study is to determine the degree of vision penalization produced by the various tint options and opaque pupil sizes offered on commercially available prosthetic contact lenses and to determine if any peripheral fusion is retained with any of these lenses.
Participants and Methods
Participants
Ten healthy volunteers, ranging in age from 18 to 30 years, were recruited from among staff members and associates of the Departments of Optometry and Ophthalmology at Wilford Hall Medical Center in San Antonio, Texas. No compensation or direct benefit was given to the volunteers. Inclusion criteria for the study included documentation of a recent complete eye examination with normal findings. All participants had been examined less than 4 months before enrollment in the study. Another abbreviated examination was performed upon enrollment to confirm ocular surface health and visual acuity, with current spectacle correction being 20/20 or better in each eye, using Smart System II PC-Plus (M & S, Chicago, IL) computer-generated charts. Each participant had stereopsis of at least 40 arcsec at 40 cm, as measured by Stereotest-Circles (Stereo Optical Co., Inc., Chicago, IL), and all exhibited normal fusion (2 red dots and 2 green dots) with the Worth 4-Dot test at 40 cm. Pupil size ranged from 3 mm to 6 mm in ambient light, as measured with a Rosenbaum gauge. Exclusion criteria included preexisting ocular conditions that precluded contact lens use, pupil size less than 3 mm or greater than 6 mm, best-corrected visual acuity less than 20/20 in either eye, strabismus, and lack of peripheral fusion by the Worth 4-Dot test.
Materials and Methods
Approval from the Institutional Review Board at Wilford Hall Medical Center was obtained. Informed consent was obtained from each volunteer, and data and files were maintained in compliance with the Health Insurance Portability and Accountability Act. Nineteen CIBA Vision DuraSoft 3 Prosthetic (D3SL) soft contact lenses with various tint patterns (www.cibavision.com) were tested. These lenses are approved by the United States Food and Drug Administration for use on seeing and nonseeing eyes and are most commonly used to create a cosmetically normal-appearing eye in cases of anterior segment injury or deformity. However, another approved indication listed is for “occlusion therapy conditions such as diplopia, amblyopia, or extreme photophobia.”9 Eighteen of the tested lenses had a base curve of 8.6 mm, diameter of 14.0 mm, and plano power. The 19th lens, the opaque occluder lens, is currently marketed with only one base curve of 8.3 mm. All lenses were made of phemfilcon A and had a water content of 55%, approved for up to 7 days of continuous wear.8 Each lens was made with one of 4 tint options: iris print color (blue or brown), iris print density (single or double layer of iris print), with or without an underprint (light or dark underprint), and an opaque pupil size of 3, 4, or 5 mm (Figure 1). One lens had a 12.5 mm black occlusive center similar to the occlusive lenses used in previous studies.
FIG 1.
Cosmetic comparison between the 12.5 mm occluder lens (left) and a prosthetic lens with a 5 mm opaque pupil (right).
Contact lenses were applied in random order to the same eye with each volunteer. Distance visual acuity in the penalized eye and presence or absence of peripheral fusion with the Worth 4-Dot test at 40 cm was determined with each lens in place and recorded. All participants were tested in the same room under the same lighting conditions. Slit-lamp examination was performed three times during each session to determine if any ocular surface disruption had occurred, in which case the session would end for the day. However, all slit-lamp exams were normal and all subjects completed the testing in a single session. The results were collated and analyzed using a 3-factor analysis of variance.
Results
Individual visual acuity with each lens ranged from 20/40 to 20/800, with mean visual acuity ranging from 20/79 to 20/620 (see Table 1). There was no significant difference in penalization of visual acuity between the blue or brown iris print (p = 0.78) or between single prints and double prints (p = 0.97). Mean visual acuity decreased with increased size of the opaque pupil. The difference between 3 mm and 5 mm pupils was significant (p = 0.01). The addition of light or dark underprint caused a significant decrease in visual acuity compared with lenses without underprint (p < 0.001). The 12.5 mm opaque occluder lens provided significantly greater penalization than lenses with light or dark underprints (p < 0.01).
Table 1. Mean visual acuity with range in parentheses for each print pattern and opaque pupil size tested
| Print pattern | 3 mm opaque pupil | 4 mm opaque pupil | 5 mm opaque pupil |
|---|---|---|---|
| Blue single-print iris | 20/80 (20/50-20/125) | 20/96 (20/50-20/125) | 20/146(20/80-20/400) |
| Brown single-print iris | 20/80 (20/40-20/125) | 20/101(20/50-20/200) | 20/158(20/80-20/200) |
| Blue double-print iris | 20/95 (20/50-20/125) | 20/136(20/80-20/200) | 20/165(20/80-20/400) |
| Brown double-print iris | 20/79 (20/50-20/125) | 20/115(20/50-20/200) | 20/161(20/80-20/400) |
| Blue iris, light underprint | 20/320 (20/200-20/400) | 20/440(20/400-20/600) | 20/400(20/200-20/600) |
| Brown iris, dark underprint | 20/400 (20/200-20/600) | 20/490(20/400-20/800) | 20/420(20/400-20/600) |
| 12.5 mm opaque occluder | 20/620 (20/400-20/800) | ||
All 8 lenses with 3 mm and 4 mm opaque pupils allowed preservation of peripheral fusion in at least 50% of subjects, while penalizing mean visual acuity to at least 20/79 (see Table 2). The lenses with 5 mm opaque pupils caused a significant decrease in peripheral fusion compared with the 3 mm (p = 0.043), yet was preserved in some subjects. Peripheral fusion was eliminated by all lenses with light and dark underprints and by the 12.5 mm print pattern on the occluder lens in all subjects.
Table 2. Percentage of patients retaining peripheral fusion for each print pattern and opaque pupil size tested
| Print pattern | 3 mm opaque pupil | 4 mm opaque pupil | 5 mm opaque pupil |
|---|---|---|---|
| Blue single-print iris | 70% | 70% | 30% |
| Brown single-print iris | 70% | 50% | 40% |
| Blue double-print iris | 80% | 50% | 40% |
| Brown double-print iris | 50% | 50% | 30% |
| Blue iris, light underprint | 0% | 0% | 0% |
| Brown iris, dark underprint | 0% | 0% | 0% |
| 12.5-mm opaque occluder lens | 0% |
Discussion
The results of this study suggest that visual penalization to therapeutic levels can be achieved by using contact lenses designed primarily for cosmetic purposes. This treatment option offers patients, parents, and providers another occlusion option that many patients and parents may find more cosmetically pleasing than many other modalities (Figure 1). Improved cosmesis may improve compliance, especially in older children who are more susceptible to social pressures. Additionally, varying the size of the opaque pupil can allow providers to tailor the degree of penalization while potentially leaving peripheral fusion intact. This could be an important factor in patients with tenuous fusion and heterophoria, which may become a tropia under other regimens. Greater penalization can be achieved with addition of underprints, but at the expense of peripheral fusion.
Disadvantages of contact lenses have to be weighed against any potential benefit before embarking on this type of therapy. Appropriate contact lens fitting and surveillance for lens-related complications can be time-consuming and costly, and it requires significant cooperation between providers, patient, and parents. Time must be spent to determine appropriate penalization and reasonable color match. As with any contact lens there is risk of keratopathy, dry eyes, abrasion, and infectious keratitis. Cost is another consideration because prosthetic lenses can cost up to $200 each. It is also important to note that standard prosthetic lenses are currently available in base curves, ranging from 7.8 mm to 9.4 mm, and diameters, ranging from 13.5 mm to 15.0 mm.1 Providers considering this form of occlusion therapy in younger children will need to know that these parameters work well for patients about 7 years of age and older but rarely work well for younger pediatric patients. Clear lenses with custom parameters can be tinted to order, including opaque pupils and underprints. Base curves of 7.3 and 7.6 mm and a diameter of 11.5 mm work well for almost all of our pediatric contact lens patients who cannot wear standard lenses. We would like to see manufacturers offer these lenses in sizes more appropriate for younger patients and make them available in 4-packs for planned replacement. Until they do, providers may find it necessary to custom tint individual occluder contact lenses for their patients younger than the ages of 5 or 6 years.
This study simply demonstrated incremental penalization capabilities of commercially available prosthetic contact lenses in normal eyes. Because we did not test this form of occlusion therapy on amblyopic patients, we cannot be certain that the degree of penalization will be the same when worn on a dominant eye or during near tasks. This modality might be the best choice for most patients, but the improvement in cosmesis may improve compliance in amblyopia treatment with older children. Future studies using amblyopic subjects might provide more insight into the use of incremental penalization with prosthetic contact lenses as a useful therapeutic option.
Literature Search
MEDLINE and OVID databases were searched from 1970 to the present with the following terms: occluder contact lenses, patching contact lenses, prosthetic contact lenses, occlusion therapy, and amblyopia therapy. Three papers reporting occlusion therapy with all-black soft contact are cited. None discussed occlusion therapy with prosthetic contact lenses or occluder lenses with variable pupil sizes.
References
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- In: Wright KW, Spiegel PH editor. Pediatric Ophthalmology and Strabismus. 2nd ed.. New York (NY): Springer-Velag; 2003;
- . The development of peripheral fusion in strabismic amblyopes using the Bangerter foil. J AAPOS. 2006;10:76
- . Randomized trial of treatment of amblyopia in children aged 7 to 17 years. Arch Ophthalmol. 2005;123:437–447
- . Treatment for amblyopia: Results using occlusive contact lens. J Pediatr Ophthalmol Strabismus. 1996;33:319–322
- . Treatment of amblyopia by extended-wear occlusion soft contact lenses. Ophthalmologica. 1994;208:214–255
- . The effectiveness of occluder contact lenses in improving occlusion compliance in patients that have failed traditional occlusion therapy. Optom Vis Sci. 2002;79:376–380
- . Tyler's Quarterly Soft Contact Lens Parameter Guide. 2007;24:32–35no. 3
- . Section III B. 1999;3;21 Dec
PII: S1091-8531(08)00150-X
doi:10.1016/j.jaapos.2008.04.008
© 2008 American Association for Pediatric Ophthalmology and Strabismus. Published by Elsevier Inc. All rights reserved.
