Extraocular muscle and Harderian gland degeneration and regeneration after exposure of rats to continuous fluorescent illumination.

Exposure of adult albino rats to continuous cool-white fluorescent illumination caused extensive destruction to the extraocular skeletal muscles (EOM's) and Harderian glands. After 1 day of exposure, leukocytes and macrophages invaded the damaged area and were found among and within the myofibers. After 48 hr of exposure, myoblasts and short myotubes extending from the damaged fibers indicated that regeneration had begun. In spite of constant illumination of the animals, the EOM's continued to reconstitute, and by the seventh day of exposure, regeneration was almost complete. At this time, small loci of degeneration and leucocytic infiltration resembling those seen in the 1-day stage again occurred. Results supported the speculation that differentiated myofibers were susceptible to the damaging effects of continuous fluorescent illumination, but that myoblasts myotubes, and early undifferentiated myofibers were not. Although the tubular epithelium proliferated in damaged Harderian glands, very few other regenerative changes were observed during the 7-day exposure period. When animals with one eye occluded with a plastic contact lens and the other unoccluded were exposed to continuous illumination, the pattern of tissue destruction in unoccluded eyes was identical to that described in the above series. However, EOM's in occluded eyes were unaffected, and Harderian glands had minimal damage limited to unshielded areas at the conjunctival fornix. Glands apparently were more susceptible to injury than EOM's. Orbital tissue destruction in these animals seemingly was due directly to a radiant energy-dependent mechanism.