Visual acuity following laser-induced hemorrhagic lesions in the fovea and parafovea: An experimental study Available to Purchase

A review of human retinal injury cases resulting from accidental laser exposure yields an ambiguous account of the importance of hemorrhagic lesions in determining the eventual visual outcome. The present investigation assessed the acute and chronic (up to 20 months) effects of laser-induced, hemorrhagic lesions located in the fovea or parafovea of six rhesus monkeys. All lesions were produced with single, 15-nsec pulses from a Nd:YAG laser (1064 nm). The visual acuity of the anesthetized animals was estimated pre- and post-exposure with the sweep-VEP, a non-invasive, objective measure. Hemorrhagic lesions in the fovea produced immediate losses in acuity to less than 20/200 (Snellen), which was the practical lower limit of resolution of the sweep-VEP technique. By one hour after exposure, however, visual acuity recovered to 20/80 - 20/100. The ultimate visual acuity in these “on-axis” animals remained about 20/80, although other changes, such as loss in temporal sensitivity, were also observed. In the animals receiving parafoveal lesions (the “off-axis” group), a more complex pattern of visual effects was observed. A hemorrhagic lesion placed at 10 degrees of visual angle from the foveal center (about 2.5mm in the rhesus monkey) produced minimal changes in acuity. In contrast, lesions placed at 5 degrees from the foveal center were similar in effect to on-axis lesions, producing large losses in acuity. The prognosis of visual acuity after off-axis lesions was better than after on-axis lesions, unless the laser injury produced an adverse tissue response, such as neovascularization, which reduced foveal function.