Distichiasis is the term used to refer to extra hairs growing on the edge of the eyelid. These hairs are not to be confused with normal hairs turning in towards the eye, which is referred to as entropion. Distichiasis hairs are extra hairs, which should not be growing there at all. They appear at a very young age. It is common and affects many breeds. It is often described as the most common congenital ocular abnormality in the dog. The problem has had little scientific attention and so it is not proven to be inherited but most vets who work with eyes assume that it is.
The effect they have on the dog is very variable probably because the hairs themselves vary between dogs. Some dogs have short soft hairs, which appear not to apply much pressure to the surface of the eye. Some are much longer and stiffer, however, and must cause the dog discomfort. How close they are to the edge of the lid, the angle they are growing at and how many the dog has are also factors which affect the degree of discomfort caused.
Distichiasis causes irritation. This usually shows itself in the dog as an increase in blink rate, holding the eye partly closed and increase in tear production showing itself as tear overflow or a "tear streak". In my experience owners are often poor judges of irritation in their dogs as they are expecting the dog to paw at the eye which they rarely do. Unfortunately it can be difficult to judge just how irritating this sort of thing is and it is definitely one of the occasions where you would like to be able to ask the dog. The diagnosis is easy if the hairs can be seen but they are quite small and easily missed. Special equipment is often required.
Several methods of treatment have been described. These include surgery (there are several techniques), freezing and electrolysis. All require a general anaesthetic, none of them is easy or foolproof and some require special equipment. Some have a reputation for causing additional problems the dog did not have to start with. Plucking is not an option as it is difficult to do it properly and the hairs grow back.
When it occurs in Weimaraners it is usually severe with numerous long stiff hairs causing obvious clinical signs. It is not possible to say what proportion of the breed have the condition as we only see the ones who are sent to us but they are certainly badly affected. The result is that pups and young dogs require one or more general anaesthetics at considerable expense before the dog is a year of age. Most vets working with eyes would definitely advise against breeding from a dog with distichiasis.
Mr J Mould MRCVS
Lecturer in Veterinary Ophthalmology
Glasgow University Veterinary School