Photoreceptor rosettes with blue cone opsin immunoreactivity in retinitis pigmentosa

Immunocytochemistry has rarely been performed on donor retinas from patients with retinitis pigmentosa (RP), due to routine storage of tissues in fixatives that reduce or destroy antigenicity. The authors have developed a method to circumvent this problem and report light and electron microscopic histopathology and immunocytochemistry of an unusual retina from a 76-year-old man with multiplex RP. The retina shows loss of photoreceptors throughout (particularly rods), shortened foveal cone outer segments, and displaced photoreceptors in rosettes and tubules, an atypical pattern for RP. Antigenicity was recovered in this retina by treatment with sodium borohydride, and 17 antigens normally found in retina are present with expected distribution, although many cells have abnormal morphology. Most cone outer segments are immunoreactive with anti-blue but not anti-red/green cone opsin, whereas blue cone sensitivity is preferentially lost in many cases of RP. Psychophysical testing of the patient's sister, who has the same retinal disease, showed reduced rod and red/green cone sensitivities. This was consistent with the diminished numbers and size of rods and red/green cones found by immunocytochemistry in her brother's retina. The sister did not show blue cone hypersensitivity characteristic of a recently described retinal degeneration known as the "enhanced S cone syndrome."