Effect of source intensity on ability to fixate: implications for laser safety.
During long-term viewing of a continuous light source, head and eye movements affect the distribution of energy deposited in the retina. Previous studies of eye movements during a fixation task provided data used for revising the safety limits for long-term viewing of such sources. These studies have been continued to determine the effect of source brightness on the nature of fixational eye movements. Volunteers fixated for 50 s on a HeNe laser (lambda = 632.8 nm) masked by a small aperture to produce a target subtending approximately 0.03 mrad in the visual field. The source was attenuated to yield corneal irradiance values in the range 0.6 pW cm(-2) to 6 microW cm(-2). Eye movements were recorded using a Dual Purkinje Image Eyetracker. The data were characterized by fixation ellipses that represent areas of the retina in which the image of the spot was located 68% of the time of each trial. Significant variation across subjects in the tightness of fixation was observed. Over the eight orders of magnitude of source brightness used in this experiment (10(-13) to 10(-6) W cm(-2)), no subject showed more than roughly a factor of two variation in the area of the fixation ellipse. No statistically significant trend in tightness of fixation as a function of source brightness was observed. There was no loss of ability to fixate, nor any drive to aversion, at the higher source intensities.
U.S. Army Medical Research Detachment, 7965 Dave Erwin Drive, Brooks City-Base, TX 78235-5108, USA. brian.lund@brooks.af.mil
Brian J
BJ
Lund
Harry
H
Zwick
David J
DJ
Lund
Bruce E
BE
Stuck
D000328:Adult; D000368:Aged; D004869:Equipment Safety / Q000379:methods / Q000592:standards; D005133:Eye Movements / Q000502:physiology* / Q000528:radiation effects*; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology / Q000528:radiation effects; D006801:Humans; D007834:Lasers; D008297:Male; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods* / Q000592:standards; D011874:Radiometry / Q000379:methods* / Q000592:standards; D015203:Reproducibility of Results; D012160:Retina / Q000502:physiology* / Q000528:radiation effects*; D012680:Sensitivity and Specificity