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Related Experiment Videos

Pattern electroretinograms after cerebral hemispherectomy.

P Azzopardi1, S M King, A Cowey

  • 1Department of Experimental Psychology, University of Oxford, South Parks Road, Oxford OX1 3UD, UK. paul.azzopardi@psy.ox.ac.uk

Brain : a Journal of Neurology
|May 17, 2001
PubMed
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Cortically blind patients after hemispherectomy retain retinal ganglion cell function, suggesting intact extrastriate cortex is needed for visual awareness, not just retinal integrity.

Area of Science:

  • Neuroscience
  • Ophthalmology
  • Visual System Research

Background:

  • Cortical blindness can result from damage to the primary visual cortex or optic radiations, sometimes with residual visual discrimination.
  • Cerebral hemispherectomy leads to hemianopia, where patients cannot discriminate visual stimuli even with forced-choice methods.
  • A hypothesis suggested that hemispherectomy causes extensive retinal ganglion cell degeneration, impairing visual information transmission.

Purpose of the Study:

  • To investigate retinal ganglion cell function in patients with cerebral hemispherectomy and functional blindness.
  • To determine if retinal degeneration explains the lack of visual discrimination after hemispherectomy.
  • To explore the role of extrastriate cortex in mediating visual responses.

Main Methods:

Related Experiment Videos

  • Assessed retinal ganglion cell function using electroretinography (ERG) in three hemispherectomized patients.
  • Recorded steady-state pattern ERGs with achromatic and chromatic stimuli from both affected and unaffected eyes.
  • Analyzed the second harmonic (2f(0)) component of the ERG signal, indicative of retinal ganglion cell function.

Main Results:

  • ERG results from hemispherectomized patients were comparable to those with striate cortex lesions.
  • No significant differences in ERG amplitude were found between the blind and sighted hemiretinae within patients.
  • Retinal ganglion cells survived in hemispherectomized patients, indicating degeneration is not the cause of functional blindness.

Conclusions:

  • The absence of residual vision after hemispherectomy is not due to complete retinal ganglion cell degeneration.
  • Intact extrastriate cortex appears necessary for voluntary responses to visual stimuli in scotomas.
  • This challenges the notion that retrograde degeneration solely explains visual field defects after extensive brain lesions.