The effect of ocular rigidity upon the characteristics of saccadic eye movements.

PURPOSE To determine whether variation in ocular rigidity (a quantity that describes the elastic properties of the globe) affects the characteristics of horizontal saccadic eye movements. METHODS Thirty-three young, visually healthy subjects participated with informed consent in the study. Axial length was measured using the IOLMaster ocular biometer. Ocular rigidity coefficients were determined using Schiotz tonometry. Horizontal saccades were stimulated randomly to 40° in 10° steps. Eye movements were recorded continuously at a sampling rate of 60 Hz using the Viewpoint video-eyetracker. RESULTS Peak velocity increased significantly with increasing ocular rigidity (F [2,263] = 30.635, P < 0.001). Time to peak velocity (F [2,263] = 27.723, P < 0.001) and total response time (F [2,263] = 21.133, P < 0.001) decreased significantly with increasing ocular rigidity. Ocular rigidity was significantly positively correlated with peak velocity (R(2) = 0.67, P < 0.001), and significantly negatively correlated with time to peak velocity (R(2) = 0.64, P < 0.001), and total response time (R(2) = 0.62, P < 0.001). CONCLUSIONS The known relationship of ocular rigidity with myopia can be extended to shorter hyperopic eyes, which are found to have higher ocular rigidity. The dynamic characteristics of saccadic eye movements are found to vary systematically with ocular rigidity. These findings suggest that the structural characteristics of the eye are an important factor in determining dynamic characteristics of eye movements.