How to give a horse his eye medications, or, What is an SPL?

One of my patients on my Large Animal Medicine rotation had a very sick eye, for which he needed approximately 9187346 medications every few hours. Getting eye meds into a horse is not easy. Their eyelid muscles are so strong that we routinely nerve block their eyelids before doing eye exams, because otherwise it would be impossible to hold their eyes open. This is, of course, not practical for hourly medications. But they hate having things put in their eyes (who doesn’t?), and they can throw their heads up very high in addition to squeezing their eyes tightly shut. This particular horse was especially tall, as well, and could hold his head well out of my arm’s reach.

The solution in these cases is to put in a sub-palpebral lavage (SPL). “Palpebral” is the science word for “having to do with eyelids,” so an SPL enables you to lavage (wash) underneath an eyelid. This is how it works: you take a big needle, which you stick through the horse’s upper eyelid coming from the underside (the side facing the eye). You use the needle to pull a slender tube through the eyelid, so that its end is sticking just under the eyelid, and the rest of the tube runs up over the horse’s head and down its neck. You affix the far end of the tube to the horse’s mane, with an injection cap on the end. In my hospital, a popsicle stick is involved in the tube/injection cap/mane connection, to stabilize the entire apparatus.

Now when you want to give an eye drop, you can use a syringe and needle to inject it through the injection cap into the tube. You then inject air after it to push it through the long tube and into the horse’s eye. They do find this annoying, and once they learn the routine, will dance around in an attempt to not let you actually stick the needle into the injection cap on their neck. However, getting at their neck is worlds easier than getting at their eye. My patient was relatively good for the whole thing, so that I could do it without asking anyone else to hold his head. He always got a cookie after each medication administration (which added up to a lot of cookies in the end). When it was over he would immediately stick his nose agaist my shirt to get his treat. The SPL was annoying for all concerned, but so much better than the alternative.