Interaction of anaesthetic drugs and UV-B irradiation in the anterior segment of the rat eye.

PURPOSE

To determine the impact of anaesthesia on acute transient cataractogenesis and ultraviolet radiation (UVR)-induced cataractogenesis.

METHODS

Sprague-Dawley rats were anaesthetized with pentobarbital, which caused almost full eyelid closure, or xylazine/ketamine, which caused eyelid retraction and proptosis. The eyelids of one eye were kept open with either a suture or adhesive tape, or both. The other eye was kept closed with either a suture or tape. Cataract was graded clinically and quantified in vitro as intensity of forward light scattering. In two UVR experiments, anaesthetized rats were irradiated unilaterally with 5 kJ/m2 UVR-B 300 nm for 15 mins. The difference between the two UVR experiments was the degree of proptosis in the pentobarbital group. Corneal drying was judged clinically with a grading scale.

RESULTS

Within 60 mins of anaesthesia induction in the first experiment, almost all lenses in open eyes developed cataract, whereas all lenses in closed eyes remained clear. In the first UVR experiment the lens light scattering was significantly higher in the xylazine/ketamine group. In the second UVR experiment the pentobarbital group was treated to achieve proptosis similar to that in the xylazine/ketamine group, which led to a smaller difference in lens light scattering between the two anaesthesia groups. Lens light scattering in the pentobarbital groups was significantly higher with forced proptosis than without prominent proptosis.

CONCLUSIONS

Xylazine/ketamine anaesthesia facilitates the development of UVR-induced cataract, whereas pentobarbital anaesthesia does not. Xylazine/ketamine anaesthesia induces more proptosis and therefore leads to increased exposure of the cornea and, secondarily, the lens.