Trauma is probably the most common problem seen by the practitioner concerning the equine eye. The eye is very prominent and horses suffering any irritation tend to rub the area around the eye quite violently. Careful examination, normally under sedation, is vital; hopefully, the orbit itself will not be affected. The clinician should make a visual examination followed by careful palpation. This will provide almost as much information as sophisticated diagnostic techniques, e.g. radiography, ultrasound (the modality of choice), CT or MRI. Some very bad head wounds will require a general anaesthetic and repair, but these are rare. Fractures to the orbital rim or zygomatic arch may well be left to heal on their own. Skin lacerations must be repaired as soon as possible under a regional block or local infiltration: the clinician will be pleased at the fast rate of healing. Antibiotics should be given parenterally to prevent infection, and NSAIDs given cautiously to control the swelling.

When suturing the eyelids it is important to use small, single interrupted stitches using a soft suture material, to avoid irritation. If the third eyelid is torn, suturing can be attempted, but careful trimming will usually be better; rarely will the third eyelid be prolapsed, and in these cases an assistant should be shown how to keep the third eyelid in position while the clinician sutures the eyelids together. These sutures need be left in situ for only 48 h; the third eyelid will remain in position after this length of time. In the extremely rare event of prolapse of the orbit, the clinician will have to be mindful of welfare considerations; unless the injury is extremely fresh, replacing the orbit and suturing the eyelids is neither a humane nor viable option – the eye should be removed under general anaesthetic.

Although this procedure could be performed in the standing horse, it is not advisable. After the horse has been anaesthetized, 10 ml local anaesthetic is injected deep behind the eye; this will allow a much lighter plane of anaesthetic for the removal of the eye. The area is prepared for surgery and, if possible, the eyelids are then sutured together and the area prepared a second time; the idea behind this is that contamination from bacteria and possible tumour cells is then contained within the orbit and will not contaminate the wound. The incision is then made very carefully through the eyelid, but not through the underlying tissue, so that the eye and the conjunctiva will be removed intact. As much of the eyelid tissue as possible is retained to allow for closure later. After the skin incision blunt dissection is used to separate the conjunctiva from the overlying tissue; the muscles have to be cut with curved scissors. Eventually, the optic nerve is cut with curved scissors and the eye is removed intact within the conjunctiva.

The incisions made in the eyelids are then sutured together with small, simple interrupted sutures after the dead space has been filled with a sterile bandage. The end of the bandage is allowed to protrude through the suture line medially. The bandage can be removed slowly on a daily basis, or in larger quantities every 5 days until the sutures are removed after 15 days. Antibiotics and NSAIDs are given at the time of the surgery and are continued for a minimum of 10 days. Fly control is essential.

Squamous cell carcinoma

The most common tumour affecting the eye, particularly in the tropics, it is thought to occur as a result of strong sunlight, as it is nearly always found in the conjunctiva of non-pigmented eyes. Usually it starts in the third eyelid, where the vigilant owner will notice it before invasion of the conjunctiva. Immediate removal is required, and it is a simple procedure. The animal is sedated and local anaesthetic instilled into the eye and conjunctiva; after 5 min the third eyelid can be grasped with a pair of tissue forceps. The tumour with a good margin is then dissected free from the third eyelid with a pair of scissors; hopefully, the cartilage of the third eyelid can be left intact. Antibiotics should be instilled into the eye, and this continued for 5 days; NSAIDs should be given by mouth. Fly control is essential. If the tumour has spread to the conjunctiva, the whole eye will need to be removed.

Equine sarcoid

Melanoma

The predilection site for melanoma is at the junction between skin and mucous membrane in the grey horse, and this includes the eye. Normally seen as round nodules about 2 mm on the rim of the eyelid, they rarely grow larger. However, as the animal ages more may appear. They are best left alone unless they enlarge quickly or begin to rub on the cornea but can be removed surgically, taking only a small margin.

This is rarely seen in just one eye: if only one eye is affected a foreign body or corneal ulcer should be suspected. Conjunctivitis may be a sign of systemic disease, so a full clinical examination should be performed. In the foal, conjunctivitis is often seen early in pneumonia; it is also seen in neonatal maladjustment syndrome. In the yearling, conjunctivitis may be a sign in mycoplasma infections; in the older animal it is likely to be associated with upper respiratory viruses.

Parasites are an important cause of conjunctivitis: Habronema muscae and Habronema majus are stomach worms normally found in small granulomata in the stomach wall; their eggs and larvae are shed in the faeces and ingested by flies, which act as the intermediate host, then the horse ingests the flies. The granulomatous stage can occur in the conjunctiva and even on the eye. Ivermectin treatment by mouth is effective, although the small granulomata may remain for some months. Onchocerca cervicalis is a common microfilarial worm also seen in the horse, and its role in ocular disease is controversial. It may certainly be seen in large numbers in cases of conjunctivitis, but it can also be seen in the normal eye. Oral treatment with ivermectin is effective, although initially following treatment the conjunctivitis appears to get worse as the worms die. Resolution is eventually complete. Thelazia lacrymalis is a specific worm in the equine eye, the adult being easily seen in the eye. Its pathogenesis is in doubt, but it is unlikely that its presence is entirely benign. It is spread by flies and controlled by oral ivermectin.