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A non-invasive method for studying an index of pupil diameter and visual performance in the rhesus monkey


Sarah J. Fairhall, Dstl Biomedical Sciences, Porton Down, Salisbury SP4 0JQ, UK. Tel.: +44 (0)1980 614392; fax: +44 (0)1980 613741; e-mail:


Background  A non-invasive model has been developed to estimate gaze direction and relative pupil diameter, in minimally restrained rhesus monkeys, to investigate the effects of low doses of ocularly administered cholinergic compounds on visual performance.

Methods  Animals were trained to co-operate with a novel device, which enabled eye movements to be recorded using modified human eye-tracking equipment, and to perform a task which determined visual threshold contrast. Responses were made by gaze transfer under twilight conditions. 4% w/v pilocarpine nitrate was studied to demonstrate the suitability of the model.

Results  Pilocarpine induced marked miosis for >3 h which was accompanied by a decrement in task performance.

Conclusions  The method obviates the need for invasive surgery and, as the position of point of gaze can be approximately defined, the approach may have utility in other areas of research involving non-human primates.