Human pupil and eyelid response to intense laser light: implications for protection

Natural ocular protective measures induced by laser glare at 514 nm were evaluated concomitant with the performance of a tracking task. Light-induced eyelid and pupil responses of 5 volunteers, 1 woman and 4 men, ages 23 to 60 years, were recorded as they tracked a target moving at 0.3 degrees/sec. with an optical sight. Frame-by-frame analysis of video images of the eye allowed assessment of the eyelid response (squint and blink) and measurement of the pupil diameter. Three laser exposure durations (0.1, 1.0, and 3.0 sec.) were used during bright and dim ambient light conditions. All laser exposure trials produced a pupillary constriction with a latency, i.e., the time from the onset of the laser exposure until the pupil began to constrict, of approximately 100 msec. In a representative 3-sec. exposure, the total intraocular energy was reduced by 69% as the pupil diameter decreased from 6.0 to 2.5 mm. For the 0.1-sec. exposures at 1.6 mW/cm2, a blink reflex was observed on 2 of 10 trials under the dim ambient conditions and not observed on 9 trials under bright conditions. For 1- and 3-sec. exposures at 0.33 mW/cm2, a blink reflex was observed on four (3 bright and 1 dim) of the 38 trials. For conditions evaluated, pupillary constriction was consistent and provided some protection when the exposure duration exceeded the pupillary latency period; however, a blink reflex was observed on only a limited number of trials, possibly due to the exposure dose, the small retinal irradiance diameter produced by the laser exposure, and the volunteers' attention to the demanding performance task.