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KR Alexander, CS Barnes, GA Fishman, AH Milam; Electrophysiological Assessment of Cone ON-Pathway Dysfunction in Melanoma-Associated Retinopathy . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1190.
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Purpose: To establish the basis for an ON-pathway abnormality of the cone system in melanoma-associated retinopathy (MAR) through analysis of the electroretinogram (ERG) and visual evoked potential (VEP). Methods: Two patients with the MAR syndrome whose sera produced strong, specific immunolabeling of retinal bipolar cells participated in the study. ERGs were recorded in response to: (1) brief flashes, (2) rapid-on and rapid-off sawtooth stimuli at a temporal frequency of 8 Hz, and (3) sinewave stimuli at temporal frequencies ranging from 8 to 96 Hz. Fundamental responses to the sinewave stimuli, derived from spectral analysis, were evaluated within the context of a vector summation model of depolarizing bipolar cell (DBC) and hyperpolarizing bipolar cell (HBC) contributions to the response fundamental (Kondo and Sieving, 2001). VEPs were recorded to the onset of luminance increments and decrements that had contrasts of 10%, 20%, and 50%. The patients’ results were compared with those of age-similar groups of 10 (ERG) and 10 (VEP) control subjects. Results: The MAR patients showed abnormal ERG responses to luminance increments, consisting of a marked attenuation of the initial portion of the b-wave, but their ERG responses to luminance decrements were normal in amplitude, timing, and waveform shape. The ERG temporal response functions of the MAR patients had normal amplitudes at frequencies of 32 Hz and higher, with a constant phase lag across these frequencies, but larger-than-normal amplitudes at frequencies below 32 Hz, and a phase lead at 8 Hz. Their VEP responses showed a marked delay to luminance increments, but only a minimal delay to decrements. Conclusion: Within the context of the vector summation model, the ERG findings from the MAR patients are more consistent with an attenuation of the DBC contribution to the ERG response than with a DBC response delay. The delayed VEP responses of the MAR patients to luminance increments may represent the response of the OFF system to increment onset.
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