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Threshold Vision in Amblyopia: Orientation and Phase

¹From the McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada; ²The School of Optometry, Queensland University of Technology, Brisbane, Queensland, Australia; and ³The Physiological Laboratory, Cambridge, United Kingdom.

PURPOSE. The visual deficit in amblyopia involves both elevated contrast thresholds and distorted suprathreshold percepts at high spatial frequencies. It is currently unclear whether these two anomalies are part of the same neural disturbance or whether they reflect different neural dysfunction.

METHODS. The quality of the spatial percepts in amblyopia was assessed at detection threshold. The ability of amblyopes to discriminate the orientation and local spatial phase of well-localized spatial stimuli was measured at the detection threshold. Measurements were made as a function of spatial frequency.

RESULTS. Performance seemed normal for orientation discrimination, even at high spatial frequencies, but, in some cases, it was disturbed in phase discrimination.

CONCLUSIONS. A different explanation and neural basis is needed to encompass both threshold and suprathreshold spatial deficits in amblyopia.