To determine whether variation in ocular rigidity (a quantity which describes
the elastic properties of the globe) affects the characteristics of
horizontal saccadic eye movements.
Thirty-three young, visually normal subjects participated with informed
consent in the study. Axial length was measured using the IOLMaster ocular
biometer (Carl Zeiss, UK). Ocular Rigidity coefficients were determined using
Schiotz tonometry. Horizontal saccades were stimulated randomly to 40 degrees
in 10 degree steps using high contrast targets presented on a CRT monitor.
Eye movements were recorded continuously at a sampling rate of 60 Hz using
the Viewpoint video-eyetracker (Arrington Research, USA).
Peak velocity increased significantly with increasing ocular rigidity
(F=30.810, df=2,263, p<0.001). Time to peak velocity (F=41.601, df=2,263
p<0.001) and total response time (F=22.167 df=2,263 p<0.001) decreased
significantly with increasing ocular rigidity. Ocular rigidity was
significantly positively correlated with peak velocity (R2=0.67,
p<0.001), and significantly negatively correlated with time to peak
velocity (R2=0.64, p<0.001), and total response time (R2=0.62,
CONCLUSION: 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 ocular globe are
an important factor in determining dynamic characteristics of eye movements.