Nature of the cone ON-pathway dysfunction in melanoma-associated retinopathy.
OBJECTIVE
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 MAR syndrome whose sera produced immunolabeling of retinal bipolar cells participated in the study. Full-field ERGs were recorded in response to brief flashes, to rapid-on and rapid-off sawtooth stimuli at a temporal frequency of 8 Hz, and to sine-wave stimuli at temporal frequencies ranging from 8 to 96 Hz. Fundamental responses to the sine-wave stimuli were evaluated within the context of a vector-summation model of the depolarizing bipolar cell (DBC) and hyperpolarizing bipolar cell (HBC) contributions to the response fundamental. 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 control subjects.


RESULTS
The patients with MAR 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 and timing. The ERG temporal response functions of the patients with MAR 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 increments but only a minimal delay to decrements.


CONCLUSIONS
Within the context of the vector-summation model, the ERG findings in the patients with MAR 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 patients with MAR to luminance increments may represent a late response of the OFF system to increment onset.
Alexander
Kenneth R
KR
Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois 60612, USA. kennalex@uic.edu
Barnes
Claire S
CS
Fishman
Gerald A
GA
Milam
Ann H
AH
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D004596:Electroretinography; D005074:Evoked Potentials, Visual; D006801:Humans; D007395:Interneurons / Q000502:physiology; D008297:Male; D008545:Melanoma / Q000150:complications / Q000503:physiopathology*; D008875:Middle Aged; D010257:Paraneoplastic Syndromes / Q000150:complications / Q000503:physiopathology*; D017949:Retinal Cone Photoreceptor Cells / Q000503:physiopathology*; D012164:Retinal Diseases / Q000209:etiology / Q000503:physiopathology*; D012878:Skin Neoplasms / Q000150:complications / Q000503:physiopathology*; D014786:Vision Disorders / Q000209:etiology / Q000503:physiopathology; D014795:Visual Pathways / Q000503:physiopathology*