Rabbit eyes, in vivo and in vitro, were exposed to UV-B irradiation at 300 nm, from a mercury arc lamp with an 11 nm bandpass filter. Radiant exposure ranged from 0.1 J/cm2 to 0.5 J/cm2. In vivo, swelling of the cornea resulted over a 12 to 40 hr period, the extent and duration being directly related to exposure. Recovery of normal thickness was complete within four days. Corneas removed at 18 hr after exposure recovered normal thickness during a five hour perfusion period, except for those most heavily exposed. When removed at 42 hr post exposure all corneas thinned to almost normal thickness. SEM showed the endothelial cells of exposed eyes to have either exaggerated villi on the surface and a disorganized mosaic or, after higher exposures, to be devoid of villi and have loose, flap like cell borders and large "blebs." After exposure of isolated corneas mounted for perfusion, swelling again ensued and similar changes were observed in the appearance of the cells, except that "blebs" were not found. No significant changes were observed in the metabolic components ATP, ascorbate and glutathione, nor was there any indication of lipid peroxidation. At higher in vivo exposures, the aqueous humor did show a decrease in ascorbate concentration and an increase in protein content, which probably result from a breakdown of the blood-aqueous barrier. UV-B irradiation may cause or promote changes in the endothelium associated with aging, but the one time radiant exposures of the magnitude used in this study, appear to have no severe or permanently toxic effects.
Whole rabbit lenses which have been fixed and dried by a critical point drying process were fractured in the dried state, and the exposed internal surfaces were examined with a scanning electron microscope (SEM). Virtually the entire field of fiber endings at a suture can be reproducibly exposed, and examined with the SEM. Other structural features of the lens fiber cells were systematically recorded at various locations from the center of the lens to the equator. The superficial, differentiating fibers tend to fracture through the cytoplasm, exposing the cell nuclei, whereas the mature fibers tend to fracture between adjacent cells, exposing cell surfaces.
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