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.
Lund
Brian J
BJ
U.S. Army Medical Research Detachment, 7965 Dave Erwin Drive, Brooks City-Base, TX 78235-5108, USA. brian.lund@brooks.af.mil
Zwick
Harry
H
Lund
David J
DJ
Stuck
Bruce E
BE
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