Entropion is a problem sometimes seen in newborn foals where the lower eyelid is rolled inward toward the globe of the eye. The entropion itself is often temporary and not difficult to correct in horses. But if left uncorrected, the entropion can cause serious secondary problems to the cornea of the horse's eye. The problem results from the irritating or abrasive effects of the eyelashes contacting the cornea.
The first thing you may notice in the way of symptoms would be tears spilling down a foal's face from the irritation. It is important to restrain the foal and manually open the lids to look for any cloudiness or ulceration of the normally smooth and clear cornea. If you see any signs of the cornea being affected, you have a potentially serious problem that needs immediate attention. The treatment in this case involves antibiotic ophthalmic ointment applied to prevent deep ulceration or rupture of the cornea from an infection of the ulcer, as well as correcting the inverted eyelid.
Correcting the inversion of the affected lid can range from something as simple as just manually rolling the eyelid to its normal position, to surgically correcting the abnormality. Surgically correcting the lid abnormality is a fairly simple procedure I do on the farm with the foal under a short-acting anesthetic.
The lid is corrected to its normal position and a thin line of tissue dissected along a line just below the lid margin. Then I suture that line closed with a thin suture material. Tissue in this area has good blood supply and usually heals very quickly. If there is no damage to the cornea, correction of the inverted lid is all that's necessary.
I see this condition fairly regularly, in about one out of every 50 foals in my practice area. It's a condition that, once you've seen it, you're not likely to miss it in evaluating a foal. Like a lot of conditions, the earlier it's noted the less likely it is to cause any serious problems.
Other conditions that can cause similar eye problems in foals are foreign bodies in the conjunctival space around the eye or trauma that scratches the corneal epithelium.