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K. Holopigian, W. Seiple, C.J. Clemens, I. Rozenbaum, R.E. Carr; Local ON and OFF System Responses in Patients with Progressive Cone Dystrophy . Invest. Ophthalmol. Vis. Sci. 2003;44(13):529.
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Purpose: Patients with cone dystrophy typically show reduced multi-focal ERG (mfERG) amplitudes within the central 10 degrees. It has been proposed that this central loss may be due to selective ON system dysfunction (Shinoda, et al., 2002). To test this proposal, we measured local ON and OFF mfERG responses in a group of patients with cone dystrophy. Methods: mfERG ON and OFF responses were recorded according to the technique of Kondo, et. al. (1998). The display was 61 scaled hexagons and each hexagon was bright for 8 frames (120 cd/m2) and dark for 8 frames (20 cd/m2) according to a binary m-sequence. mfERGs were recorded with a bipolar Burian-Allen contact lens electrode. The results for a group of patients with progressive cone dystrophy (acuity range 20/25-20/125) were compared to age-similar control subjects. A patient with fundus albipunctatus (visual acuity 20/20-) was also examined. Results: For analysis, the results from the individual hexagons were averaged into four rings. Templates based on the control subjects’ data were created for the ON and the OFF responses in each ring. These templates were fit separately for the patients’ ON and the OFF responses. The patients with cone dystrophy had ON and OFF responses that were reduced in amplitude to approximately 25% of the control values. There was no difference in the magnitude of the loss for the ON and OFF systems. In contrast, the patient with fundus albipunctatus showed a larger loss for the ON system responses than for the OFF system responses at all eccentricities. Conclusions: Patients with cone dystrophy do not show selective ON system defects since both ON and OFF system responses were equally impaired. 1. Shinoda, et al. (2002). Acta Opthalmol Scan 80, 219. 2. Kondo, et al. (1998). Invest Opthalmol Vis Sci 39, 574.
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