Fixation Stability in Monkeys with Strabismus

Purpose: To assess the effect of target parameters on fixation stability in strabismic monkeys. Methods: Eye movements were recorded in one normal and three strabismic monkeys during 72 fixation conditions (4 shapes; 3 sizes; 2 backgrounds; OD, OS or OU viewing), each repeated 5 times. Fixation stability was quantified using the Bivariate Contour Ellipse Area (BCEA). Influence of target parameters was assessed using 4-way ANOVA. Results: BCEA was greater in the strabismic monkeys compared to the normal. In strabismus, BCEA of the deviated eye was significantly greater than BCEA in the fixating eye. Target shape and size significantly influenced fixation stability in both normal and strabismic monkeys. Background effects were idiosyncratic. Conclusions: Target parameters that influence fixation stability in a normal, also affects fixation stability in disease conditions such as strabismus. Target parameter influences likely function via conjugate mechanisms since proportional effects were observed in both viewing and covered eyes.