'On' response defect in paraneoplastic night blindness with cutaneous malignant melanoma

Response properties of rod and cone systems were assessed in a patient with an acquired form of night blindness associated with a metastatic cutaneous malignant melanoma. The night blindness, a sensation of shimmering lights, and selective reductions in the amplitudes of both rod and cone electroretinographic (ERG) b-waves were present before and after chemotherapy, confirming that this disorder was a paraneoplastic consequence of the melanoma rather than a response to chemotherapy. During ERG testing with flashes of extended duration, the cone b-wave abnormality was found to be a predominant loss of the cone ERG 'on' response with relative preservation of the 'off' response, similar to that observed in patients with congenital stationary night blindness. An impairment in signal transmission specific for retinal 'on' pathways may be a primary defect in both of these forms of night blindness.