Abstract

Laser induced morphology in the primate retina and associated changes in visual functioning D.O. Robbins1, H. Zwick2, B.E. Stuck2. Dept of Psychology, Ohio Wesleyan University, Delaware, OH1; USAMRD Walter Reed Army Institute of Research, San Antonio, TX2.

Purpose: Non-human primates exposed to laser pulses while performing a visual task demonstrated partial acuity and focal contrast sensitivity recovery in spite of induced morphological damage. An examination of the morphological nature of these punctate retinal lesions was made to help explain the resilience of visual functioning. Methods: Six retinae exposed to Nd/YAG pulses were evaluated for morphological changes using color funduscopy, confocal scanning laser ophthalmoscopy (CSLO), angiography, and optical coherence tomography (OCT). Exposures varied in energy from 0.1 mJ to 100 mJ, representing energies equivalent to 10 times below to 10 times above the injury dose. Results: Exposures made at or above threshold injury produced prolonged recovery times with the highest doses resulting in the greatest permanent visual loss in the exposed region. Overall, visual acuity was generally more resilient to cumulative injury than was focal contrast sensitivity. Color funduscopy in foveally exposed retinae revealed a punctate pattern of tightly clustered foveal lesions and a less tightly packed macular punctate lesion pattern for parafoveal exposures. Disruption of the retinal nerve fiber layer (NFL) in the papillomacular bundle was evident for both foveal and parafoveal exposures. OCT in animals receiving high dose foveal exposures revealed significant thinning of the foveal pit from 0 to 80 mm compared to 150 mm for non-exposed foveae. At lower dose levels (0.1 mJ), OCT scans revealed a normal foveal pit thickness but the foveal pit was slightly broader and NFL thickness in the papillomacular bundle was abnormal. Both fluorescein and ICG angiography demonstrated minimal evidence of retinal or choroidal vascular disruption. Conclusions: Morphological observations of laser exposed retinae suggest significant damage in the foveal and papillomacular bundle with minimal alteration to deeper pigment epithelial cells and the choroidal vasculature. The preservation of these deeper layers may be associated with photoreceptor reorganization and may ultimately account for the later preservation of visual function after even intense laser irradiation.