Abstract

Morphology and histopathology of laser induced macular pathology in behaviorally-trained, non-human primates D.O. Robbins1, H. Zwick2, S.T. Schuschereba2, B.E. Stuck2. Department of Psychology, Ohio Wesleyan University, Delaware, OH1; USAMRD Walter Reed Army Institute of Research, San Antonio, TX2.

Purpose: To evaluate the retinal morphology and histopathology of behaviorally trained and exposed non-human primates (NHP) that demonstrated visual acuity improvements in the presence of laser-induced maculopathies. Methods: Stable photopic acuity (< 1 min of arc) was established in five animals using a Landolt ring acuity task. Awake, task-oriented animals were exposed to Q-switched (20 Hz), 10 nsec, 532 nm Nd/YAG laser pulses that were presented either focally (on-axis) or parafoveally (off-axis). Each eye received repeated exposures over an extended time period (years) and wide range energies from 0.1 mJ (10X below ED50) to 100 mJ (just below retinal hemorrhage). Macular lesion patterns were assessed with color ophthalmoscopy, scanning laser ophthalmoscopy (SLO), fluorescein and indocyanine green (ICG) angiography, optical coherence tomography (OCT) and histopathology. Results: Repeated suprathreshold on-axis exposures produced small punctate lesions centered on the fovea. Off-axis exposures produced a more widely distributed pattern of punctate lesions. Flourescein angiography for both types of exposures showed high reflectivity emanating from the lesions sites. ICG angiography shows high reflectivity emanating from choroidal vessels within the lesion sites. OCT measurements revealed a thinner foveal pit for on-axis lesion patterns (0 to 50 m). No evidence of foveal scaring was observed using either SLO or OCT. Histopathology revealed macular photoreceptor loss, discontinuities in photoreceptor synaptic zones and reduction of RPE melanin. In addition significant accumulation of macular exudate and spheroidal lipid inclusions appeared in many RPE cells. The spatial extent of these cellular pathologies appears more focal for on-axis than off-axis exposures. Evidence of druesen was minimal under both conditions. Conclusions: Morphology and histopathology for repeated suprathreshold exposures demonstrated significant retinal pathology in animals still capable of relatively high visual function suggesting higher order neural reorganization and modulation of weaker retinal signaling.