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ON-pathway dysfunction in a patient with acquired unilateral night blindness
C S Barnes1, M G Brigell, K R Alexander
1Department of Neurology, and the Neuroscience and Aging Institute, Loyola University Chicago, Maywood, Illinois 60153, USA.
Purpose:
To investigate possible functional correlates of an apparent ON-pathway defect observed in the cone electroretinogram of a patient with acquired unilateral night blindness.
Method:
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.
Results:
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.
Conclusions:
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.