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Editors Selection IGR 9-4

Examination methods: Cortical visual function

Comment by Christopher Bowd on:

13819 Depth perception deficits in glaucoma suspects, Gupta N; Krishnadev N; Hamstra SJ et al., British Journal of Ophthalmology, 2006; 90: 979-981

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Recent histological, electrophysiological and fMRI evidence suggests that LGN and visual cortex structure and function are compromised in glaucoma. In the current study, Gupta et al. (IGR 8-2: 409) provide what might be additional evidence of geniculo-cortical pathway deficits in glaucoma patients (n = 18) and glaucoma suspects (by disc or IOP, n = 16). The authors report significant decreases in stereoacuity in these groups, compared to healthy participants (n = 19), and suggest that this finding may be attributable to a relative delay in cortical input from one eye relative to the other affecting cortical binocular interactions (as the authors acknowledge, an alternate explanation for these findings is a spatial sampling defect at the retinal ganglion cell level undetected by perimetry).

While the differences in stereoacuity are large among groups (148.1 arcsec, 144.1 arcsec and 26.6 arcsec, respectively, for glaucoma, suspect and healthy participants), the magnitude of the measurements (and their accuracy) is likely influenced by the stereoacuity assessment technique used. The Frisby test takes a sensory continuum of disparity values (a continuous variable) and renders it a discrete variable with an artificial range (ranging between 20 arcsec and 340 arcsec) with large intervals (ranging between 20 arcsec and 190 arcsec) essentially making stereoacuity 'measurements' rough estimates. Overall the significant results of Gupta and colleagues are intriguing and it would be very interesting to more accurately quantify the differences in stereoacuity among glaucoma, glaucoma suspect and healthy individuals using a rigorous psychophysical technique.

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