Acute reversible cataract induced by xylazine and by ketamine-xylazine anesthesia in rats and mice.

Combined administration of ketamine and xylazine is used increasingly for safe, effective anesthesia of small laboratory animals. We found that rats injected systemically with ketamine and xylazine at doses recommended for effective anesthesia developed acute reversible lens opacities. Mice given the same drug doses were similarly affected. Testing of each drug alone demonstrated that xylazine was the causative agent. The appearance of cataract was associated to varying degree with proptosis, suppression of the blink reflex, corneal surface drying, and mydriasis. All of these ocular effects, including cataract also could be induced locally by topical application of xylazine to one eye, with untreated contralateral eyes showing no drug effects. A possible cause of xylazine-induced transient lens opacification is trans-corneal water loss and alteration of aqueous humor composition due to corneal exposure. Additional action on aqueous humor formation and the lens itself may be due to the alpha-2-adrenoceptor nature of xylazine. Whatever the cause of cataract induction, the occurrence of this phenomenon during ketamine-xylazine anesthesia appears to be associated with marked changes in the physiological state of the eye. Therefore, the side-effects of anesthetic drug combination should be considered prior to its use on animals for studies of ocular physiology.