The severity and characteristics of retinal injury following laser radiation derived from laser and tissue related factors.
We have previously shown that retinal damage following Nd:YAG Q-switched laser radiation in rabbits was related to
physical parameters, i.e. energy levels and number of pulses. Yet, an extremely large variability in the severity of the
damage was found under similar exposure paradigms, even within the same retina. This emphasizes the role of the
biological variables in the pathological mechanism of laser-induced retinal damage.
The aim of the present study was to further study histological parameters of the injury in relation to retinal site and to
elucidate their role in the initiation and characteristics of the damage, following various energy levels (10-50 &mgr;J) and
number of pulses (1-4).
Pigmented rabbits were exposed to Nd:YAG laser radiation (532nm, pulse duration: 20ns). Exposures were conducted in
retina tissue, adjacent to the optic nerve, with a total of 20 exposures per retina. Animals were sacrificed 15 min or 24
hours post exposure, eyes enucleated and processed for paraffin embedding. 4&mgr;m thick serial sections, stained with
hematoxylin and eosin, were examined under light microscopy.
Two major types of retinal damage were observed: focal edema confined to the pigmented epithelium and the
photoreceptor cells, and hemorrhages, associated with destruction of retinal tissue. While focal edema associated with
slight elevation of the photoreceptor layer seems to depend on the pigmented epithelium, hemorrhages were related also
to the choroid vasculature at the site of radiation. It is suggested that a thermo-mechanical mechanism is involved in laser
induced retinal hemorrhages at energies above 10-30&mgr;J (2-1 pulses, respectively).