Effect of retinal illuminance on visual acuity, visual fields and contrast sensitivity in patients with glaucoma, albinism and diabetics retinopathy
Mokhua, Matieho Belina
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Introduction: Individuals with low vision may have reduced or impaired visual acuity, visual fields, and contrast sensitivity. This may lead to impaired visual functioning, orientation and mobility. In addition, those patients may have binocular defects, colour defects and poor visual processing. Patients who are visually impaired as a result of diabetic retinopathy, albinism, and glaucoma have difficulties with execution of many visuallyguided daily tasks. Visually impaired patients in these three groups (diabetic retinopathy, albinism and glaucoma) report that their visual abilities are very dependent on lighting conditions. Filters and tinted lenses are often prescribed to low vision patients to mainly reduce their discomfort and sometimes provide improved visual performance. Method: Cross-sectional comparative design was used to examine the effect of changing retinal illumination on visual acuity, contrast sensitivity, and visual fields in participants with albinism, diabetic retinopathy and glaucoma. Measurements of these visual functions were made with and without 4% transmission neutral grey filters (NoIR U23). Results: In response to reducing the retinal illumination, there was an average significant reduction of 0.12±0.08 log units in visual acuity for participants with albinism whilst there was a significant reduction of 0.34±0.22 log units in contrast sensitivity. Glaucoma participants showed the average significant reduction in visual acuity of 0.06±0.08 log units and an average significant reduction in contrast sensitivity of 0.25±0.18 log units. Diabetic retinopathy showed the average non-significant reduction of 0.06±0.14 log units in visual acuity and a significant reduction of 0.31±0.15 log units in contrast sensitivity. Central visual fields in albinism participants showed no defects either with or without the NoIR U23 filter. Seven glaucoma participants did not show any visual field defects, whereas nine showed fields defect with the NoIR U23 filter. Four participants with glaucoma showed an improvement with the NoIR U23 filter. On the 50 points scale used for quantifying visual field size, glaucoma participants showed an average reduction of 1.6±13.3 points in response to the filters. In diabetic retinopathy participants, the average visual fields showed a significant reduction of 6.7±11.7 with the NoIR U23 filter. Eight diabetic retinopathy participants showed fields defects, and twelve did not have any visual fields defects. Conclusion: Reducing the retinal illuminance generally causes vision to become worse. Visual acuity and contrast sensitivity become worse with the NoIR U23 filter. Where there are central visual field defects with no filter, then these defects usually become larger with the filter in place. Visual field testing showed no defects for any of the albinism participants either with or without the NoIR U23 filter. Within each of the three low vision groups, there are large variations in the responses to the reduction of light entering the eye. Some individuals showed substantial changes in response to changes in lighting conditions while others, with the same ocular condition showed little or no change. This has implications for the clinician when prescribing filters. Attention should be given to the individual patient and the way in which they respond to reductions in light levels.