There will be no doubt in any horse owner’s mind that it is particularly important to seek veterinary help as soon as you notice any problem with your horse’s eye. Veterinary surgeons in practice deal with a wide range of conditions, from simple conjunctivitis, to more complex conditions such as uveitis or trauma. Many cases will be managed by your vet at your premises. However, sometimes it is necessary for your vet to refer your horse for specialist evaluation or treatment. In this article, we explore some of the more common reasons for your vet to suggest referral. 

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In general there are four main reasons for suggesting referral; the need for surgery, specialist treatment, specialist diagnostic modalities or for a second opinion. 

Trauma:

The most usual eye injury in horses is a superficial corneal ulcer, where several layers of the corneal are removed by abrasion. Uncomplicated ulcers usually resolve with treatment and management at home with topical treatments prescribed by the vet and administered by the owner. However, in unusual cases, where for example a fungal infection is involved or if the ulcer is not responding to treatment, your vet may suggest hospitalisation for further investigation or intensive treatment. Penetrating eye injuries, or those that threaten the integrity of the globe often need to be referred immediately for surgical treatment at a veterinary hospital.

Occasionally, trauma can lead to damage to the eyelids. It is critically important to treat eyelid lacerations quickly in order to maintain the integrity of the eyelids themselves. Horses are very reliant on their eyelids and eyelashes to keep the surface of the eye moist and clear from dust and dirt. If they lose a significant portion of the eyelid, this may lead to secondary ulcerations or damage to the cornea. Many cases of eyelid lacerations can be managed in the field, but in severe cases, the horse may need repair under surgical conditions. 

Ocular or periocular tumours:

The most commonly seen tumours in the periocular region are squamous cell carcinomas, periocular sarcoids, lymphomas, mast cell tumours and melanocytic tumours (which may also occur in the eye). Simple, early cases of for example, a squamous cell carcinoma of the conjunctiva or third eyelid are often treated in the field if surgery to remove the third eyelid with or without the addition of a chemotherapy drug, if this is likely to be curative. More advanced cases or those in inoperable areas such as the eyelid tend to need additional, sometimes multimodal therapy with chemotherapeutics or specialised treatment such as radiotherapy, strontium plesiotherapy or electrochemotherapy. Very few treatment centres offer such specialised therapies and as such, your horse may need to be referred for evaluation and treatment. 

If you look closely at your horse’s eye, you may notice small, irregular protrusions from the edge of the pupil. These are called the corpora nigra. They can develop into cyst-like structures known as corpora nigra cysts. These are benign and usually asymptomatic. However, occasionally they can grow so large that they might be associated with unusual behaviour, visual disturbances, headshaking or refusal to jump. In these cases, your vet may suggest referral for evaluation and treatment, usually with transcorneal laser or aspiration of the cyst to reduce it in size. 

Recurrent uveitis:

What is recurrent uveitis? This is a chronic, debilitating, inflammatory condition of the eye. Also known as ERU or “Moon blindness” (as it was incorrectly thought to coincide with phases of the moon). Up to 19% of horses worldwide are thought to be affected. Horses tend to suffer from repeated episodes of painful inflammation in the eye, followed by periods where the eye is comfortable and quiescent. Over time, the horse may eventually become blind. In the first instance, early cases of uveitis tend to be managed at home, with the use of topical anti-inflammatories, or steroids and a drug to dilate the pupil. 

Many cases will respond well to this treatment for first or subsequent episodes. However, some cases become exceedingly difficult to manage and some horses may have suffered from multiple low-grade episodes before they are first noted. Repeated episodes will cause considerable discomfort to the horse, not to mention the anxiety and financial burden felt by the owner. Your vet may choose to refer a case like this for evaluation and treatment by a specialist. Some of these cases may be suitable for specialist treatment. Treatment includes options such as surgery to remove inflammatory cells or the implantation of an implant or cyclosporine to control this inflammation. In some cases, the disease may have progressed to the point where enucleation is necessary. 

Pre-purchase examination:

It is common practice for veterinary surgeons to carry out a detailed examination or vetting of horses prior to sale. As part of this process, a detailed examination of the eye will be performed. In many cases, the eye will be found to be free of clinically significant abnormalities. However, the scope of this examination is to determine whether or not the horse is “suitable for the use intended”. Sometimes lesions will be found that are of questionable significance without further examination. For example, an opacity in the lens may develop further or remain static; which could possibly have an impact upon the resale value of the animal. When such issues are encountered, it is normal practice to offer referral to a specialist ophthalmologist for a second opinion and more detailed examination to ensure that the most comprehensive advice can be given. 

Of course, a second opinion is not always limited to a pre-purchase examination; veterinary surgeons in practice will occasionally refer unusual cases for evaluation by a specialist, to diagnose or to confirm the original diagnosis. 

The decision to refer will be made by your veterinary surgeon once they have evaluated your horse and the problem

All cases are different, and situations vary. Some horses can be managed easily at home, and some may need to be referred for management reasons alone. For example if the horse is very distressed by treatment; or if facilities such as stabling are needed and the owner does not have access. Sometimes in specific cases, discussion of the case with a specialist following digital images may be sufficient; otherwise they will need to be referred for specialist evaluation and therapy in person. If you have any concerns, please speak to your veterinary surgeon; who will be able to advise based on your personal circumstances. 

Further reading:

Further reading: