Developmental Medicine & Child Neurology



Case Report

Conscious visual abilities in a patient with early bilateral occipital damage


Deborah Giaschi  a1 c1, James E Jan  a2, Bruce Bjornson  a2, Simon Au Young  a3, Matthew Tata  a4, Christopher J Lyons  a1, William V Good  a5 and Peter KH Wong  a2
a1 Department of Ophthalmology, University of British Columbia (UBC), Vancouver, British Columbia, Canada.
a2 Department of Pediatrics, UBC, Canada.
a3 Department of Pediatrics, British Columbia's Children's Hospital, Canada.
a4 Department of Psychology, UBC , Canada.
a5 Smith-Kettlewell Eye Research Institute, San Francisco, CA, USA.

Abstract

A 21-year-old male presented with occipital lobes that were extensively damaged by bilateral infarcts present at birth. The absence of the striate cortex was confirmed with anatomic and functional MRI and high-resolution EEG. His cortical visual impairment was severe, but he retained a remarkable ability to see fast-moving stimuli. Horizontal optokinetic nystagmus could be elicited from either eye. Resolution acuity was close to normal providing the patient was allowed to move his head and eyes. The direction of motion in random-dot patterns could be discriminated with perfect accuracy at speeds above 2 deg/s, and the patient reported that he could ‘see’ the motion at fast but not at slow speeds. This conscious residual vision for motion is known as Riddoch's phenomenon, but it has never been reported in the complete absence of the striate cortex. Functional neuroimaging revealed activation that was outside the motion-responsive regions of the extrastriate cortex. This case demonstrates remarkable plasticity in the human visual system and may have implications for understanding the functional organization of the motion pathways.

(Accepted May 28 2003)


Correspondence:
c1 Department of Ophthalmology, BC's Children's Hospital, Room A146, 4480 Oak Street, Vancouver, BC, V6H 3V4, Canada. E-mail: giaschi@interchange.ubc.ca