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There are many causes of lumps developing in and around horses’ eyes, several of them serious and a few of little importance. The difficulty for owners is to know which warrant veterinary attention and which do not. However, for your own peace of mind it has to be worth asking your vet to investigate any lump. It is often helpful if you can tell your vet how quickly the lump has developed. Fast-expanding masses will usually generate more concern.

The majority of lumps will need prompt attention due to their location, even if in themselves they are not important. Anything that affects the movement of the eyelid, or the efficiency with which it wipes the surface of the eye, will have a profound implication for the integrity of the cornea (the clear window of the eye). More than 75% of the blink is done with the upper lid, so deformities and loss of function in it are much more serious than in the lower lid.

Any lump that results in an abnormal rubbing of the cornea is likely to result in an ulcer — this is potentially extremely serious. Some masses are on the eye itself or on the internal membrane of the eye (conjunctiva) and these can vary in their significance.

Lumps in the eyelid

Eyelid lumps are divided into several types based on the cause. First, there are those arising from infection — whether from a wound or other injury or an infection affecting the eyelid glands (so-called “styes”).

Second, there are lumps that arise from some deformity of the skin or its associated glands and hair follicles. These are rare in horses. Quite often, they are spotted incidentally or when the eye starts to produce an abnormal discharge, which may simply be the result of a lack of proper tear drainage from the eye.

Another unusual lump is caused by a prolapse (abnormal positioning) of the fat pad behind and around the eye. This can be alarming but is not always visible. When the horse lowers its head and blinks, the mass may look large and when it is standing and the eye is relaxed, it may disappear altogether. The chief feature of the early stages of this unusual condition is that it causes neither obvious discomfort nor inflammation.

Trauma or bruising of the eyelid can cause serious thickening and obvious bruising of the eyelids (and sometimes of the eye itself). A bruise around the eye associated with swelling should sound a warning bell that there might have been a bout of colic.

Even when a horse is cast, it seldom causes excessive bruising or grazing of the eyelids. With such knocks, the swelling of the eyelid may be relatively trivial, but it should always be checked in case there is deeper damage, for example, on the eye itself.

Virus papilloma (true “warts”) are benign skin tumours that arise from a viral infection. In young horses (usually those under two or three years old) they will invariably resolve without intervention. In older horses there is less tendency to self-cure and some remain for life.

Tumours and tumour-like masses

There are several important tumours that occur in the eyelid regions and these cause some concern. Not all are serious, but almost all will have secondary implications on eyelid function. Some are small but potentially serious, while others are larger and have less long-term, harmful effects. Early recognition is important if treatments are to be effective.

Eyelid melanoma is only common in grey horses. Usually, melanomas remain quite localised and the lower lid is more often involved. This is fortunate because it means treatment involving surgical excision can be carried out relatively easily.

Melanomas can be recognised by their shiny black colour. However, some occur on the inner lining of the eyelid, so, apart from distortion, there may be nothing to see. It may be easy to examine the margin of the lower lid and it is probably worth checking this if a swelling is seen on a grey horse. The inner corner of the eye and the structures inside the eye can also be affected.

We still have no real idea why melanomas develop and even less idea about how to treat them. Apart from surgical removal, which can be difficult, the sole suggested medical approach is the daily administration of a drug called cimetidine. This is used to treat gastric ulcers, but there are reports of it being effective against some melanomas. However, the eyelid is particularly resistant to this approach and very few cases respond to it.

The other option is to leave the mass alone, but this should be reserved for slow-growing localised lesions or those that are clearly impossible to treat. As melanomas are largely the preserve of older grey horses, other masses are common, especially under the tail and around the mouth. A few cases are highly malignant, but these are rare.

Sarcoids and carcinomas

The sarcoid is probably the most common eyelid problem and is potentially serious. Sarcoids appear in many different forms ranging from mild hair loss to large nodules under the skin and fleshy outgrowths. This makes diagnosis difficult, but treatment is easier the earlier it can be applied. By the time the condition is extensive or large, the options for treatment are limited.

The sarcoid doesn’t spread to internal organs, but it is common for a horse to have more than one lesion, so it is always worth checking places such as the groin and girth area. The best form of treatment is radiation — around the eye, this carries a success rate of more than 90%, but it is an expensive and restricted method of treatment. There are other options, but all are less effective. Surgical excision and topical creams are not usually advisable because they will cause tissue destruction and scarring.

One of the most dangerous eyelid tumours is squamous cell carcinoma. This affects the eyelid (or eye) especially in horses with pale eyelid margins or third eyelids. There are two main types of squamous cell carcinoma recognised by vets. The proliferative form appears as larger masses, while the destructive form results in erosion and destruction of the local tissues. The proliferative form is normally followed by the destructive and should be recognised quickly so action can be taken.

This condition also occurs on the surface of the eye, and in all cases there is a risk of malignancy and spread to adjacent structures. In the most advanced cases, the tumour can spread to other internal organs. The options for treatment are again limited by practicality and the need to kill every single tumour cell.

By the time such carcinomas are seen by a vet there is often already extensive destruction of the eyelid margins, so the scope for surgical repair is limited and involves significant reconstructive surgery. Surgical excision of tumours on the cornea and the third eyelid is, however, entirely feasible in most cases, except severely neglected ones.

There are options for medical treatment using anti-cancer eye drops or ointments in early cases, and in some such small tumours it may be possible for freeze the tumour. Inevitably there is risk that either the treatment is applied too late or will not remove the whole lesion. As is typical with cancers of any type, treatment has to kill or remove every single cancer cell — if just one is left behind, there is a strong possibility of recurrence, usually in a more aggressive form.

Although some unusual tumours occur in and around the eye, the most common ones are easily recognised. Confirmation of a diagnosis is usually reliant on biopsy, tissue scrapes or aspirates from the mass. The outlook is often far better than is first appreciated, provided diagnosis is made early.

In very rare types of tumour, it is usually not possible to give an idea of the realistic prognosis, and treatment methods are poorly characterised. Few vets have seen all the options, so in some circumstances the case may be best referred to a specialist centre for diagnosis and treatment.

  • This veterinary feature was first published in Horse & Hound (2 February ’06)
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