Purchase this article with an account.
VE Das, S Ono, RJ Tusa, MJ Mustari; Saccade Gain Adaptation in Monkeys With Strabismus . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2653.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: We have found that monkeys reared with alternate monocular occlusion (AMO) have normal visual acuity, but develop incomitant strabismus and disconjugate saccades (Fu et al., 01). Previous studies in human subjects with strabismus have suggested that saccade disconjugacy may be due to an inability to adapt saccade amplitudes to asymmetries inherent in the oculomotor plant of each eye. In this study we have attempted to directly test saccadic gain adaptation in monkeys with strabismus. Methods: We recorded eye movements using binocular search coils in 1 monkey with esotropia, 1 monkey with exotropia and 1 normal monkey. We used a backward-step paradigm to reduce the gain of 10 and 15 deg saccades by 30% during monocular viewing of each eye. Results: The backward-step paradigm resulted in an exponential reduction of saccadic gain that reached asymptotic values after 300-700 saccades in normal and strabismic monkeys. When we compared the average gain of the first 25 saccades to the last 25 saccades during adaptation in the strabismic monkeys, we found the gain reduction ranged 18-23% in the viewing eye and 12-18% in the non-viewing eye. This difference suggests that the viewing eye adapted more than the non-viewing eye. Since this method of analysis does not take into account the pre-adaptation saccade disconjugacy, we created a model for saccadic gain adaptation that included the variation of ocular misalignment with orbital position. When we compared the exponential fit of saccadic adaptation there was no significant difference in the rate of decay (time constant) for the viewing and non-viewing eye as predicted by the model. Furthermore, the difference in scaling of the exponential fit was also predicted by the model. Conclusion: Our results show that monkeys with strabismus are capable of adapting saccadic gain equally well in each eye. This suggests that the disconjugate saccades in these monkeys are not due to deficiencies in saccadic adaptation mechanisms per se. Our results also indirectly suggest that the saccade generator for the two eyes is common thus supporting Hering«s law of equal innervation. (Fu et al., Soc Neurosci., 01).
This PDF is available to Subscribers Only