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(Investigative Ophthalmology and Visual Science. 2006;47:5288-5294.)
© 2006 by The Association for Research in Vision and Ophthalmology, Inc.
DOI:  10.1167/iovs.06-0539
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Reflexive Optokinetic Nystagmus in Younger and Older Observers under Photopic and Mesopic Viewing Conditions

Trevor J. Hine,1 Guy Wallis,2 Joanne M. Wood,3 and Efty P. Stavrou3

1From the Applied Cognitive Neuroscience Research Centre, School of Psychology, Griffith University, Mt. Gravatt, Queensland, Australia; the 2School of Human Movement Studies, University of Queensland, St. Lucia, Queensland, Australia; and the 3Centre for Health Research (Optometry), Queensland University of Technology, Kelvin Grove, Queensland, Australia.

PURPOSE. To investigate the effect of age on optokinetic nystagmus (OKN) in response to stimuli designed to preferentially stimulate the M-pathway.

METHOD. OKN was recorded in 10 younger (32.3 ± 5.98 years) and 10 older (65.6 ± 6.53) subjects with normal vision. Vertical gratings of 0.43 or 1.08 cpd drifting at 5°/s or 20°/s and presented at either 8% or 80% contrast were displayed on a large screen as full-field stimulation, central stimulation within a central Gaussian-blurred window of 15° diameter, or peripheral stimulation outside this window. All conditions apart from the high-contrast condition were presented in a random order at two light levels, mesopic (1.8 cdm–2) and photopic (71.5 cdm–2).

RESULTS. Partial-field data indicated that central stimulation, mesopic light levels, and lower temporal frequency each significantly increased slow-phase velocity (SPV). Although there was no overall difference between groups for partial-field stimulation, full-field stimulation, or low-contrast stimulation, a change in illumination revealed a significant interaction with age: there was a larger decrease in SPV going from photopic to mesopic conditions for the older group than the younger group, especially for higher temporal frequency stimulation.

CONCLUSIONS. OKN becomes reflexive in conditions conducive to M-pathway stimulation, and this rOKN response is significantly diminished in older healthy adults than in younger healthy adults, indicative of decreased M-pathway sensitivity.






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Copyright © 2006 by the Association for Research in Vision and Ophthalmology