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Proceedings Paper

Ocular dynamics and visual tracking performance after Q-switched laser exposure
Author(s): Harry Zwick; Bruce E. Stuck; David J. Lund; Maqsood Nawim
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Paper Abstract

In previous investigations of q-switched laser retinal exposure in awake task oriented non-human primates (NHPs), the threshold for retinal damage occurred well below that of the threshold for permanent visual function loss. Visual function measures used in these studies involved measures of visual acuity and contrast sensitivity. In the present study, we examine the same relationship for q-switched laser exposure using a visual performance task, where task dependency involves more parafoveal than foveal retina. NHPs were trained on a visual pursuit motor tracking performance task that required maintaining a small HeNe laser spot (0.3 degrees) centered in a slowly moving (0.5deg/sec) annulus. When NHPs reliably produced visual target tracking efficiencies > 80%, single q-switched laser exposures (7 nsec) were made coaxially with the line of sight of the moving target. An infrared camera imaged the pupil during exposure to obtain the pupillary response to the laser flash. Retinal images were obtained with a scanning laser ophthalmoscope 3 days post exposure under ketamine and nembutol anesthesia. Q-switched visible laser exposures at twice the damage threshold produced small (about 50?m) retinal lesions temporal to the fovea; deficits in NHP visual pursuit tracking were transient, demonstrating full recovery to baseline within a single tracking session. Post exposure analysis of the pupillary response demonstrated that the exposure flash entered the pupil, followed by 90 msec refractory period and than a 12 % pupillary contraction within 1.5 sec from the onset of laser exposure. At 6 times the morphological threshold damage level for 532 nm q-switched exposure, longer term losses in NHP pursuit tracking performance were observed. In summary, q-switched laser exposure appears to have a higher threshold for permanent visual performance loss than the corresponding threshold to produce retinal threshold injury. Mechanisms of neural plasticity within the retina and at higher visual brain centers may mediate the stability of visual function and performance metrics. Long term repeated exposure to the retina, however, may eventually dampen the ability of higher visual brain centers to detect declining retinal neural output from cumulative retinal damage. Individuals chronically exposed to such laser sources should have more frequent ophthalmic retinal surveillance.

Paper Details

Date Published: 17 May 2001
PDF: 8 pages
Proc. SPIE 4246, Laser and Noncoherent Light Ocular Effects: Epidemiology, Prevention, and Treatment, (17 May 2001); doi: 10.1117/12.426724
Show Author Affiliations
Harry Zwick, Walter Reed Army Institute of Research (United States)
Bruce E. Stuck, Walter Reed Army Institute of Research (United States)
David J. Lund, Walter Reed Army Institute of Research (United States)
Maqsood Nawim, Walter Reed Army Institute of Research (United States)

Published in SPIE Proceedings Vol. 4246:
Laser and Noncoherent Light Ocular Effects: Epidemiology, Prevention, and Treatment
Bruce E. Stuck; Michael Belkin, Editor(s)

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