Evidence is consolidated to support the hypothesis that long periods of almost complete light exclusion will have therapeutic benefit for patients with early stages of hereditary retinitis pigmentosa. The hypothesis is based on observations on effects of light on photoreceptors of normal rats and on photoreceptors of rats with either vitamin A deficiency or hereditary retinal dystrophy, on electrophysiological studies of patients with early retinitis pigmentosa, and on measurements of retinal oxygen utilization in humans and animals with retinal degenerations. Almost complete light exclusion can be best accomplished with an opaque flush-fitting scleral contact lens. If this hypothesis is correct and light exclusion is begun in the earliest stages, it may be possible to double the patient's visual lifetime by keeping one retina in reserve in darkness while the other retina functions but degenerates in light.
Berson EL. Light Deprivation for Early Retinitis Pigmentosa: A Hypothesis. Arch Ophthalmol. 1971;85(5):521–529. doi:10.1001/archopht.1971.00990050523001
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