ON-pathway dysfunction in a patient with acquired unilateral night blindness

To investigate possible functional correlates of an apparent ON-pathway defect observed in the cone electroretinogram of a patient with acquired unilateral night blindness.

Visual evoked potentials were recorded to the onset of a grid pattern consisting of either incremental or decremental squares. Saccadic eye movements were measured to luminance increments and decrements presented 5 degrees from fixation. The patient's results were compared with normative data.

Visual evoked potential latencies were prolonged to incremental stimulation of the patient's affected left eye but were within normal limits for the other three conditions (increments and decrements, right eye; decrements, left eye). A similar pattern of asymmetry between latencies to incremental and decremental stimulation of the affected eye was observed for saccadic eye movements.

The observed predominant delay in response to luminance increments supports the hypothesis of an ON-pathway dysfunction in this patient with acquired unilateral night blindness.