Ophthalmology
The Equine Referral Hospital offers a comprehensive ophthalmology service including medical and surgical treatment of all types of ocular disease as well as pre-purchase examination second opinions. We have a complete range of equipment to carry out detailed examination of all parts the eye, including a slit lamp biomicroscope, tonography and ultrasonography.
Eye diseases are common in horses and some, especially corneal injuries and infections can deteriorate rapidly despite receiving treatment. We have a large care team of equine clinicians, nurses and students who provide round the clock supervision and intensive therapy of complicated eye cases including subpalpebral lavage systems to provide continuous medication of the eye.
We have expertise in all types of equine eye disease including
- Corneal injuries, ulcers and infections
- Diagnosis and treatment of glaucoma
- Assessment and treatment of cataracts
- Recurrent uveitis
- Assessment of retinal disease
- Treatment of ocular tumours including sarcoids and squamous cell carcinoma
Corneal ulcers
Corneal ulcers usually start when a horse traumatises the surface of the eye, and then bacteria infect the defect. In most cases, these ulcers heal without any complications, but in some cases, especially if aggressive types of bacteria are present, the ulcer can become very large and very deep. Intensive, round the clock treatments may be required to save the eye in these situations. Using a specialised subpalpebral lavage catheter allows us to place medications directly onto the surface of the eye without having to physically open the eyelids, increasing the comfort for the horse.
Above: A horse with a subpalpebral lavage catheter in situ (left) to apply medication to a corneal ulcer (right).
Glaucoma
Glaucoma is a condition that causes an increased build up of fluid in the eye, and thus an increased pressure within the eye (‘increased intraocular pressure’). As a result, horses with glaucoma may have a large eye that seems to protrude from the head more than normal. The cornea (surface of the eye) may also look cloudy, as the increased pressure prevents fluid within the cornea from being effectively removed. Luckily glaucoma is a rare condition in horses, and it usually results from inflammation due to recurrent uveitis (see ‘ERU’ section). Treatment for glaucoma can involve placement of drops to decrease the fluid build up in the eye, as well as treating the uveitis if it is present.
Above: a photograph of a horse with glaucoma
Equine recurrent uveitis
Equine recurrent uveitis (ERU) is a common condition in horses. Horses with ERU have intermittent episodes of eye pain – they may squint, have discharge from the eyes and avoid bright light. The term uveitis refers to inflammation within the eye, and in horses with ERU, this inflammation flares up periodically. Although there are many proposed reasons for this inflammation, there is no one unifying theory that explains ERU. Treating ERU can be challenging and frustrating for both owners and vets. It is usually relatively easy to treat a single episode, by applying anti-inflammatory drugs to the eye and by giving drugs such as Finadyne (flunixin) to decrease pain and inflammation, but these treatments do not seem to stop further episodes. More recently, a drug called cyclosporine A, which helps control inflammation by controlling the immune system, has been used successfully in horses to minimize ongoing inflammation and recurrent episodes in horses with ERU. Cyclosporine drops are not effective however, as they do not penetrate through the surface of the eye to the area that is inflamed. Instead, researchers in the USA have developed small implants that are surgically placed in the sclera (the white tissue around the eye). These implants slowly release the cyclosporine over a period of up to 5 years. The Equine Referral Hospital is one of the few institutions in the UK that are utilising these cyclosporine implants. For further information, see http://www.cvm.ncsu.edu/vth/clinical_services/ophthal/opthal_cyclo.html
The retina
The retina is the membrane at the back of the eye that recognises light, transmitting images via the optic nerve to the brain. The retina is thus essential for vision. Retinal abnormalities are common in horses and can occur for a variety of reasons. The only way to diagnose retinal abnormalities is via an ophthalmoscope, a hand held device which allows one operator to see the retina. At the Equine Referral Hospital, we have a specialised ophthalmoscope that allows real-time viewing of the retina via a video screen, so that the retina can be viewed by several people at once. In addition to this, images can be captured which then form part of the horse’s medical record, and can be re-evaluated at a later date to assess any changes in the retina.
Cataracts
Horses can develop cataracts, just like people. Cataracts are opacities in the lens. The lens' function is to focus light rays on the retina, and cataracts decrease vision by interfering with light reaching the retina. Cataracts can be congenital (the horse is born with the cataract) or acquired. In acquired cases, cataracts often develop in horses with uveitis. Although cataracts can interfere with vision, in most cases horses appear to cope well with cataracts, even in both eyes, and so no treatment is usually required. However, in rare cases, such as in a horse with bilateral (both eyes) congenital cataracts, surgery can be performed to remove then lens – unlike in people, horses seem to cope well without the lens!
Squamous cell carcinoma
Squamous cell carcinoma is a common cancer of the horse’s eye. The cancer most commonly grows on the third eyelid, but can also grow on the surface of the eye itself. Removing the tumour via surgery is the most successful way of preventing recurrence, but in some cases complete removal is not possible (for example if the tumour is on the surface of the eye). In these cases, additional treatment is required to kill any remaining cancerous cells. Mitomycin C is a drug which is applied onto the surface of the eye, killing cancer cells, whilst not harming normal cells. Mitomycin C has only recently been used in equine medicine, and here at the ERH we are currently treating several horses with this medication.