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CT Trevethan, A Sahraie, L Weiskrantz; Pupillometric Investigation of Spatial Vision in Cortically Blind . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3907.
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Purpose: Pupillary responses elicited by the onset of spatial gratings with space-averaged luminance matched to the background, have been reported to provide an objective measure of spatial processing in normal observers. A previous study has also demonstrated their presence in a cortically blind subject. We aimed to investigate whether such findings can be generalised and whether the technique can be applied to probe for spatial processing within the field defect of six cortically blind subjects. Methods:Sinusoidal grating stimuli were generated on a PC and presented on a calibrated SVGA monitor. The pupillary responses were recorded using an ASL5000 pupillometer with modified head-rest mounted optics providing a resolution better than 0.01mm. The stimulus target was a static, vertical sinewave grating (spatial frequency range 0.5 - 7 cycle/degrees) presented within a circular aperture subtending 10 degrees at a viewing distance of 760mm. The space-averaged luminance matched the background. The pupillary responses were obtained for both sighted and blindfield stimulus presentations. Results: We have demonstrated pupil grating responses to a range of spatial frequencies within the blindfield of 5 out of the 6 cortically blind subjects tested. The blindfield response amplitudes were attenuated and the peak sensitivity is shifted to lower spatial frequencies compared to sighted field responses. Conclusion: Pupil grating responses have been demonstrated in 5 out of 6 hemianopic subjects tested. All the subjects with a clear blindfield pupil grating responses, also showed evidence for blindsight when tested psychophysically. The results support the view that pupillometry is a useful technique for detection of residual spatial channels and screening for blindsight.
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