Because of the wide variety of patterns exhibited both genetically and clinically, retinitis pigmentosa may be considered better as a degenerative retinal process than a specific disease entity. When selected for its most typical manifestations, however, retinitis pigmentosa appears as a well recognized and distinct retinopathy.Psychophysical and physiological techniques have gradually been accumulating evidence on the pathogenesis of this disease. Careful examination of dark adaptation reveals that both rod and cone thresholds are affected more severely.1,2 At certain stages the rod-free fovea can have the lowest thresholds to all visible wavelengths,1,3 a condition not observed in normal vision. This inversion in the normal threshold contours of the retina has been well delineated by Zeavin and Wald4 who emphasized the disease's unique selectivity for affecting rod vision.The profound reduction of the electroretinogram (ERG) at most stages of the retinopathy imply that the process involves large
GOURAS P, CARR RE. Electrophysiological Studies in Early Retinitis Pigmentosa. Arch Ophthalmol. 1964;72(1):104–110. doi:10.1001/archopht.1964.00970020106022
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