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Rodney Stedall M.C. Optom (UK) Dip Optom FOA (SA)
Hazel Sacharowitz Dip Optom FOA (SA) FAAO
Ria Theotakanis Dip Optom FOA (SA)

Abstract: The authors proposed that fi tting a Plano iris-tinted contact lens (clear pupil) to a person with oculocutaneous albinism will increase visual comfort by reducing glare sensitivity. The study concerns the hypothesis that there will be an improvement in contrast sensitivity as well as a reduction in glare discomfort when using this mode of treatment. Subjects were fi tted with either a Plano iris tinted contact lens with a clear pupil (experimental group) or with a clear Plano contact lens (control group). Contrast sensitivity was measured in both groups with and without a simulated glare source.

Results showed a signifi cant difference in contrast values in the experimental group when comparing results with and without the contact lens under glare conditions. For the control group, no signifi cant difference was noted under no glare conditions, yet under glare conditions, one eye showed signifi cant difference. It was further noted that the mean contrast sensitivity of the experimental group seemed to improve in all settings (with and without glare) after the fi tting of an iris tinted contact lens. Due to the small number of subjects in this study, we cannot however conclusively say that visual comfort was enhanced with the fi tting of iris tinted contact lenses.

Oculocutaneous albinism is the most common type of albinism in Africa1,2. Persons with oculocutaneous albinism are characterised by varying degrees of congenital hypopigmentation3,4 including a reduction in the pigment melanin in the hair, skin and eyes. Low vision management5 options are often directed towards controlling illumination with tinted lenses, ultraviolet protection coatings, aperture or coloured contact lenses, visors and hats to reduce symptoms of photophobia. In the normally pigmented eye, iris pigmentation controls the amount of light entering the eye. However, the lack of iris pigmentation in a person with albinism may result in the person experiencing disabling glare and reduced visual function in bright surroundings. Rubin6 describes disability glare as glare that reduces visibility of a target due to the presence of a light source elsewhere in the visual fi eld. Light from the glare source is scattered by the ocular media and forms a veiling luminance which reduces the contrast and thus the visibility of the target. Discomfort glare on the other hand, refers to the sensation experienced when the overall illumination is too bright, for example when the sun is refl ected off a shiny surface such as a windscreen. The complaint of sensitivity to light and trouble seeing in the bright sun in persons with albinism was assumed to be as a result of reduced contrast sensitivity in the presence of glare (disability glare). Disability glare responses can be obtained by comparing conventional visual function tests such as visual acuity or contrast sensitivity in the presence and absence of a glare source.

Methods and materials
Twenty four subjects between the ages of 11 and 20 years where randomly fi tted with either clear (control group) or iris-tinted (experimental group) Plano soft contact lenses. All subjects were scholars from Prinshof School for the Visually Impaired and were identified as having oculocutaneous albinism. Eleven of the subjects of mixed gender where randomly allocated in the control group and the remaining thirteen subjects formed the experimental group as can be seen in Table 1.

Subjects wearing habitual spectacle corrections were instructed not to remove the spectacles during all testing procedures. Visual acuity was assessed using the EDTRS high contrast acuity chart7 at standard illumination levels. Contrast sensitivity was repeatedly measured with the Pelli-Robson Contrast Sensitivity Chart8-10 Clement Clark at standard room illumination with and without a glare source.

The assessment was divided into six stages and each stage was administered and recorded by the same examiner throughout the study in order to maintain consistency and increase accuracy. Visual acuity was assessed in the first stage using the high contrast Lighthouse Distance Visual Acuity Test Chart11 at the appropriate testing distance and with standard illumination. A sequence of measuring right eye distance visual acuity followed by measurement of the left eye and then both eyes was followed throughout the study. Results were scored12 by recording the total number of letters read correctly. Each letter read added one point to the score; each line added five points. This method follows the ETDRS protocol and was shown by Raasch et al13 to provide greater accuracy when multiple measurements have to be averaged, compared or otherwise statistically manipulated.

Contrast sensitivity levels were then measured using the Pelli- Robson letter sensitivity chart with and without a simulated glare stimulus. Glare was simulated using a round 22 watt fl uorescent 21cm bulb mounted in a black plastic cone that was positioned at a distance of 15cm from the eye base as can be seen in Figure 1.

The glare source can be a spot, bar, ring of light or an extended bright background according to Rubin6. Extended glare sources, such as the annulus produced by a circular fl uorescent tube, cause fewer afterimage problems and are said to be better accepted by patients14. Two charts with different letter sequences but otherwise identical were positioned at a distance of 1 meter from the subject at the level of the subject's eyes. The luminance of the white areas was approximately 100cd/m2. In keeping with the scoring protocol of the Pelli- Robson chart, subjects were instructed to read each letter across the chart starting with the dark letters in the upper left-hand corner. A forced choice procedure whereby the subject is asked to identify the letters and the examiner determines whether the answers are correct or incorrect was followed. Subjects were instructed to continue until two of the three letters in a triplet were read incorrectly. Forced-choice tests yield more reliable results than criteriondependent tests, especially with unpracticed observers15. The mean results were calculated for the right eye, left eye and both eyes and are represented in Table 2.

Subjects were then randomly fitted with either a clear soft contact lens or an iris-tinted soft contact lens illustrated in Figure 2. The control iris-tinted contact lens used was a disposable clear Plano Proclear lens with a light transmission at 560nm of 94%. The experimental subjects were fitted with Plano Hydron Z6 contact lenses that were tinted in a "doughnut" fashion using a dark amber brown tint with a 4.5mm clear pupil and 11.5mm outside diameter. The clear pupil had a visible light transmission of 94% and the amber tint measured 14% transmission at 560nm which is similar to the 17% absorption of natural melanin pigment16 of the eye. Pupil size and iris colour were noted. All subjects were given a minimum of fi fteen minutes to adapt to the contact lenses and then asked a series of questions as indicated in Table 3 relating to day-to-day adaptations to glare sensitivity. The subjects were then reassessed for contrast sensitivity using the Pelli-Robson sensitivity chart with the same non-glare and glare test sequence and procedure as before the contact lens was inserted. The right contact lens was removed standing near an external glare source and the subject was asked to compare the two eyes and questioned as to which eye was now more sensitive to light.

Disability glare can be modeled in terms of veiling luminance scattered into the test target from a glare source. The veiling luminance effectively reduces image contrast and the amount of scattered glare light determines the magnitude of contrast deduction. In a study of glare sensitivity with simulated ocular turbidity, the glare light caused contrast sensitivity to decline rapidly, while acuity remained near normal17. Tests based on contrast sensitivity measures should therefore be more sensitive to disability glare than tests based on acuity alone. The Pelli-Robson chart has been widely used by researchers and was chosen as it is easy for young subjects to understand due to its similarity to letter acuity testing, it is fast to administer and has proven18-20 reliability. This variable contrast chart consists of 16 triplets of letters arranged in 8 rows of two triplets each. The letters remain constant in size and each subtends 2.8 degrees at a 1 meter test distance. As the subjects read across the chart the letters reduce in contrast. The last triplet in which the subject reads 2 of 3 letters correctly, determines the level of contrast sensitivity. Ruben6 reported that it makes sense to measure contrast sensitivity to assess disability glare due to the phenomenon that disability glare can be modeled in terms of veiling luminance scattered into the test target from the glare source. The veiling luminance effectively reduces image contrast. The amount of scattered glare light will determine the magnitude of the contrast reduction and thus contrast sensitivity is measured in order to assess disability glare.

The reduction of pigment in both the anterior and the posterior segment of an oculo-cutaneous albinotic eye produces diffused intraocular light and increased ocular light scatter within the eye. Van den Berg21 reported that people with retinal hypopigmentation have increased intra-ocular light scatter. Rosenblum et al22 used colored fi lters to study their effect on visual function in visually impaired subjects with different kinds of ocular pathology. All subjects including those with albinism, reported subjective improvement including reduction of photophobia, eyestrain and eye discomfort. These results correlate with verbal responses to the questionnaire in this study. Hoeft and Hughs23 found that subjects with albinism benefi ted from amber tints with a gradual cut-off at 500nm. Dark amber fi lters which cut off the short-wave part of the spectrum signifi cantly decrease light sensitivity and diminish symptoms of photophobia and high glare sensitivity. Barron24 suggested that opaque artifi cial iris lenses and dark translucent tinted lenses may reduce photophobia and glare by creating an artifi cial light stop. Iris tinted soft contact lenses with an amber brown tint in a "doughnut-like" fashion where thus designed for this preliminary study.

Statistical analysis using before and confounding variables confi rmed no signifi cant difference in the experimental and control groups. A comparison of the contrast sensitivity results before a contact lens was fi tted with and without simulated glare is presented in Table 4.

The mean value is represented. The bracketed value is the standard deviation. Similarly, Table 5 represents the mean value of the contrast sensitivity for each group after being fi tted with either a clear or tinted contact lens. Statistically no signifi cant difference was found between the control and experimental groups thus making the groups comparable. Table 6 represents outcome results when comparing the mean results with and without an iris-tinted contact lens under the different glare conditions. The value in brackets represents the Signifi cance or "p" value. A "p value" less than 0.05 in the experimental group represent a significant difference in results when comparing subjects with and without the contact lens. A "p" value greater than 0.05 in the control group represents a signifi cant difference in results when comparing subjects with and without the contact lens. The outcome results show a signifi cant difference in contrast values in the experimental group when comparing results with and without a contact lens under glare conditions. The results without glare are not as conclusive possibly due to the small number of subjects in the study. However, when studying the slope in the Figures 3 and 4, the mean contrast sensitivity of the experimental groups increased in all settings (with and without glare) after the fi tting of an iristinted contact lens. The gradient of the slope of the control group indicates that the clear contact lens had less effect on the contrast sensitivity findings.

Eye care practitioners are aware that many patients with albinism complain of visual discomfort in bright light. Responses from the questionnaire confi rm this clinical impression and reduced contrast sensitivity responses under simulated glare confi rm a change in the visual system. However, we cannot conclusively say that visual discomfort was improved with the fi tting of iris tinted contact lenses probably due to the small number of subjects in the study. The contact lenses provided a natural appearance when indoors and outdoors and were readily accepted by the subjects. Further research is indicated to relate disability glare fi ndings to the subjective visual comfort experienced.

We wish to thank Cooper Vision (SA) (Pty) Ltd for sponsoring the contact lenses and Prinshof School for the Visually Impaired for their support.

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