Laser-induced acute and long-term alterations to visual fuction

摘要

We examined acute laser exposure effects in awake task- oriented non-human primates. These animals were trained to discriminate between various acuity targets that initially exceeded 1 minute of arc. They were exposed in the fovea and parafovea by aligning the output from a laser source with the gap of threshold Landolt ring. Parafoveal exposures were produced by offsetting the laser source and Landolt ring gap by 1 degree. For small spot exposures ($LS 100 $mu@m) using repetitively pulsed (20 Hz) Q-switched laser (532 nm) pulses above the retinal damage threshold, initial acuity deficits returned to pre-exposure baseline acuity within 30 minute postexposure. Periodic ophthalmoscopic examinations revealed punctate lesions within the fovea as well as parafoveal region. Off-axis exposures produced a greater abundance of parafoveal punctate lesions. With repetitive exposures over a period of 6 months to one year, immediate postexposure recoveries in visual acuity lengthened from minutes to hours and eventually the initial deficits became permanent. These results suggest that Q-switched visible laser pulses may induced photoreceptor pathology prior to the observance of significant acuity changes and/or initiation of the photochemical transduction process. If this hypothesis is correct, Q-switched laser damage may be more selective to the outer segment of the photoreceptor where the transduction mechanism presumably is resident.