Night blindness with depolarizing pattern of ON/OFF response in electroretinogram: a case report

To present a patient who has night blindness with a depolarizing pattern of ON/OFF response by electroretinography (ERG).

A 43-year-old woman had had night blindness and poorly corrected visual acuity since childhood. Parental consanguinity was noted. The patient had suffered from mental retardation, epilepsy, and mild cerebellar ataxia. Corrected visual acuity was 20/30 in the right eye and 20/25 in the left. Goldmann perimetry showed no scotoma but slight depression with internal isoptors. No evidence for rod activity was observed by Goldmann-Weekers adaptometry. The ocular fundi appeared normal.

Conventional full-field ERGs to scotopic (dim and bright flash) and photopic (bright flash and flicker) stimuli were recorded. Photopic ERG responses to long flash stimulation (200 ms) were also examined.

The scotopic responses to dim flash were non-recordable, while those to bright flash were severely reduced. The photopic responses to bright flash were decreased. The amplitudes of flicker responses also were significantly decreased, and the implicit times of those responses were prolonged. Although the amplitudes of a- and d-waves to long flash stimulation were reduced, those of the b-wave were within normal range. The implicit times of a-, b- and d-waves were significantly prolonged. The patient showed a normal rise for the photopic b-wave but lacked a normal falling slope after the b-wave peak. An OFF-response late-negativity was also noted.

The abnormal ON/OFF response found in the patient could be diagnosed as depolarizing pattern, characterized by elevation of the plateau to a positive potential above the prestimulus baseline. Since the ERG waveforms and clinical features found in our patient were different from those in previous reports, her ERG findings might reflect another retinal physiological mechanism.