Fixational eye movements in normal and pathological vision
Section snippets
Fixational eye movements in normal vision
Eye movements during fixation are necessary to overcome loss of vision due to adaptive neural mechanisms that normalize responses across neurons in the face of unchanging or uniform visual stimulation. Thus, the goal of oculomotor fixational mechanisms may not be retinal stabilization, but rather controlled image motion adjusted so as to overcome adaptation in an optimal fashion for visual processing (Skavenski et al., 1979). In the early 1950s, it was shown that all eye movements could be
Abnormal eye movements during fixation
Impaired fixational eye movements are observed in patients with a variety of central and peripheral pathologies (Shakhnovich and Thomas, 1974, Shakhnovich and Thomas, 1977; Ciuffreda and Tannen, 1995). Although we spend about 80% percent of our waking lives fixating our gaze, the contribution of impaired fixational eye movements to vision loss is generally overlooked. This gap in knowledge has prevented the field from developing new treatments and early diagnostic tools to ameliorate those
Conclusions
Approximately 80% of our visual experience happens during fixation. During the other 20% of the time we are virtually blind, due to saccadic suppression mechanisms. Therefore, understanding the neural and perceptual effects of fixational eye movements is crucial to understanding vision.
Fixational eye movements were first measured in the 1950s, but sometime during the 1970s, the field arrived at an impasse due to difficulties in data collection, discrepancies in results by different
Abbreviations
- LGN
lateral geniculate nucleus of the thalamus
- RF
receptive field
- V1
primary visual cortex
Acknowledgments
Drs. R. John Leigh, Stephen Macknik, and Xoana Troncoso read the manuscript and made helpful comments. I am very grateful to Dr. R. John Leigh for graciously providing Fig. 9, Fig. 10, and for his insights and discussion of slow saccades, square-wave jerks, and many other concepts addressed here. Thanks also to Dr. David Sparks for helpful discussion and for pointing me to the Van Gisbergen and colleagues’ studies on the generation of microsaccades. Thomas Dyar and Dr. Xoana Troncoso helped
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