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Markus Groppe, Charles L. Cottriall, Rukhsana Safa, Susan M. Downes, Robert E. MacLaren; Identification And Functional Assessment Of Residual Cones Present In Eyes With End Stage Retinal Dystrophy. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4593.
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A recent report identified the presence of residual non-functional cones in patients with end-stage rod cone dystrophies. We therefore sought to identify the prevalence of residual cones in a large cohort of patients with end-stage retinal dystrophy and to identify any specific functional test which might demonstrate survival of these cells in the presence of otherwise extremely poor vision.
Thirty eyes of thirty patients with end-stage inherited retinal degeneration (26 retinitis pigmentosa and 4 cone-rod dystrophy) underwent comprehensive ophthalmic examination including visual acuity, electrical evoked phosphene (EEP) threshold, spectral-domain optical coherence tomography (OCT), fundus photography and pupillometry.
Most patients achieved perception of light vision (n=25). The remainder had either peripheral hand movement detection (n=3) or no light perception (n=2). In 9 eyes residual foveal cones were found on OCT examination. Patients with residual foveal cones had significantly increased phosphene sensitivity to electrical stimulation, as evidenced by a lower rheobase compared to eyes without cones (0.87mA vs 1.43mA, p=0.03). There was a significant linear correlation between residual pupil constriction and minimum threshold for electrically evoked phosphenes (p=0.019),but no significant difference in patients with and without residual cones in their light pupil constriction reflex (p=0.12).
Patients with endstage retinitis pigmentosa and cone-rod dystrophy with low or absent vision demonstrate residual visual function on pupillometry and EEP, suggesting that these tests may useful in detecting surviving cells. We identified a subgroup of retinitis pigmentosa patients with residual foveal cones who have an increased sensitivity to electrical currents but do not show an improved light pupil constriction reflex. This supports the observation that these cells do not respond to light but their presence may be associated with improved sensitivity to electrical stimuli.
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