Acute Threshold Damage, Minimal Spot, Q-Switched Exposure Effects on Focal Contrast Sensitivity

摘要

In previous investigations of minimal spot, q-switched laser visible (532 nm) on-line pulsed laser exposure, non-human primate (NHPs) required up to 13 times the retinal damage threshold for the emergence of permanent visual acuity dysfunction. In the present experiment, a Landolt ring contrast sensitivity task, employing 4 NHPs trained on a Landolt ring contrast sensitivity task, was employed to determine the effect of threshold retinal damage (532 nm, 3 microjoules, 20 Hz, PRF) on the slope of the NHP Landolt ring contrast sensitivity function measured under repeated threshold exposure conditions. All four animals initially showed uniform deficits in contrast sensitivity requiring about 6 to 16 min post exposure for complete recovery. Over several months of repeated exposures made in 3 NHPs, a steepening of the contrast sensitivity slopes appeared, manifested by an inability to measure sensitivity for the finest Landolt ring spatial frequencies and an associated enhancement in the mid and lower spatial frequencies. In one animal that had undergone a longer period of repeated threshold laser exposure, the slope of its contrast sensitivity function shifted to a uniform deficit relative to pre exposure with an inability to provide sensitivity measurements above 20 Hz/deg, demonstrating an abrupt loss in the ability to measure the higher spatial frequencies associated with maximal optimal visual acuity. Ophthalmic retinal observations demonstrated the presence of punctate lesions induced by minimal spot foveal exposure. These data support measurements of high contrast acuity undergoing repeated q-switched exposure at damaging levels. While the acuity in such exposure situations eventually undergoes a permanent deficits, measurements of the entire contrast sensitivity function, in which acuity function maybe obtained at and above 60 Hz/deg, may reveal enhanced lower spatial frequency sensitivity as well as permanent a permanent deficits in higher spatial frequencies.