| Popis: |
Eye movements are important to fixate or track an object of interest in the visual field. Eye movements are coordinated by six extraocular muscles (EOM) [1, 2]. These EOMs are responsible for ensuring that the visual axes of both eyes are parallel to each other [1, 2]. The effect of variation in refractive error upon eye movements has not received the same attention in the literature as the sensory aspect. Axial length varies considerably with refractive error [3-8]. Subjects with myopia have been found to have considerably larger eyes, with a longer axial length and lower ocular rigidity [3-5, 7, 8], compared to subjects who are emmetropic or hyperopic [3, 4, 6, 9]. It has also been shown that subjects with hyperopia have significantly smaller eyes with shorter axial lengths [6] and higher ocular rigidity [9]. Despite these marked differences in the physical characteristics of the eye between subjects, little work has been done to examine whether axial length or ocular rigidity influences eye movement response characteristics. The effect of variations in the structural characteristics of the eye upon the eye movement characteristics were explored in this PhD work by measuring eye movements under a number of experimental saccadic, smooth pursuit and vergence paradigms in 93 young visually normal subjects. This thesis showed that the characteristics of saccadic eye movements varied systematically with ocular rigidity. Subjects with lower ocular rigidity (always myopic) produced saccades with significantly slower peak velocity and a longer time to peak velocity. Conversely, subjects with high ocular rigidity (hyperopic) produced saccades with significantly faster peak velocity and a shorter time to peak velocity compared to both emmetropes (medium ocular rigidity) and myopes. Smooth pursuit responses to sinusoidal stimulus movement also varied significantly with ocular rigidity. Subjects with lower ocular rigidity (myopic) showed significantly lower response gain and larger phase lag. Hyperopes showed significantly more accurate responses with higher response gain and lower phase lag compared to emmetropes and myopes. Disparity vergence responses to a sinusoidal moving 3D stimulus varied systematically with ocular rigidity. The high ocular rigidity hyperopic eyes showed significantly higher response gain and lower phase lag than the other two refractive groups. The low ocular rigidity myopic eyes exhibited significantly lower response gain and longer phase lag than the medium ocular rigidity emmetropic eyes. The viewing time has a significant influence upon response quality as both response gain and phase lag deteriorates significantly over a very short period of time. In conclusion, it has been shown in this thesis and for the first time that the dynamic characteristics of saccadic, smooth pursuit and disparity vergence eye movements vary systematically with the structural characteristics of the globe. The results of this work provide substantial evidence of the influence of ocular rigidity upon the characteristics of eye movements. |
