Ophthalmology
Staff
Jane Sansom BVSc DVOphthal DipECVO FRCVS
Keith Barnett OBE MA PhD BSc DVOphthal FRCVS DipECVO DipACVO
David Donaldson BVSc(Hons) DipECVO MRCVS
Claudia Hartley BVSc DipECVO MRCVS
Claudia Busse DVM CertVOphthal MRCVS
Màrian Matas DVM MRCVS
About Ophthalmology
The Unit of Comparative Ophthalmology offers a fully comprehensive referral service in the treatment of both medical and surgical conditions that affect the equine eye. All our staff have received specialist training in ophthalmology and the clinician in charge of a case will have either a European or British Diploma in Veterinary Ophthalmology, which requires five years of specialist training. In addition, we have the support of other experienced colleagues in anaesthesia and imaging, where in-depth investigations are required in addition to ophthalmoscopy.
Eyelids: The most important function of the eyelids is to protect the eye and, for this reason, they are frequently subject to trauma. When this occurs, it is important that not only the lids but the eye is evaluated thoroughly and this can be difficult as the tissues become very tender and swollen. Imaging, either in the form of ocular ultrasonography or radiography, can be extremely useful to determine whether the damage is superficial or deep.
Conjunctiva and third eyelid: The conjunctiva lines the lids and covers the third eyelid, having a protective as well as a lubricating function. It is not unusual for foreign bodies to become trapped within the conjunctival sac or behind the third eyelid. This case demonstrates how difficult it can be to find these foreign bodies, which can be extremely small. This horse had an uncomfortable eye for several months before being referred to the Animal Health Trust. Using a slit lamp biomicroscope, it was possible to identify a small foreign body embedded in the conjunctiva of this upper lid. On histopathology, this turned out to be plant material. Successful removal resulted in a pain free and visual eye.
Cornea: The cornea or front window of the eye is vulnerable, particularly in the horse, to a large number of conditions that can result in permanent blindness or loss of the globe. It is important for any corneal lesion that every attempt is made to arrive at an accurate diagnosis as early as possible. A significant number of infectious agents can cause inflammation and ulceration. One of the most devastating problems is keratomycosis, or a fungal infection of the cornea. Why the horse should be so predisposed is not entirely clear, except that it lives in a “mouldy” environment. Fungal keratomycosis frequently follows on from traumatic injuries and long term antibiotic treatment. Outlined below are some of the presentations that we have seen for this condition.
Uveal tract: Diseases of the uvea are relatively common in the horse. The visible part of the uveal tract is the iris and forms the coloured part of the eye. Inflammation of this structure is known as iritis or uveitis. Repeated bouts of inflammation are referred to as recurrent uveitis, periodic ophthalmia or moon blindness. This is a very serious condition, ultimately blindness can result if the disease is not well controlled. Whatever the cause of the uveitis, the presentation is the same. However, if a horse has had repeated attacks of uveitis, it is possible from an eye examination to pick up changes indicative of a past history of problems. This is obviously extremely important as part of a vetting procedure. Between attacks of uveitis, the eye may appear relatively normal. Not all cases of uveitis fall into the category of periodic ophthalmia or recurrent uveitis.
Lens: Like the cornea, this is normally a transparent structure that lies behind the iris. It is important that it is optically clear, so that it can function to focus light onto the retina. Unfortunately, an opacity of this structure, known as cataract, can impair vision. There are a large number of causes for cataracts. Uveitis is a common cause of secondary cataract. Unfortunately, some horses are born with cataract (congenital cataract) as illustrated below. Surgical removal of the cataracts in these cases can be performed successfully and will give the animal some guidance vision. Advances are being made in this area and it is likely that, in the near future, artificial lenses will be used to give the horse the ability to focus.
Pre-purchase examination: A significant number of our referred cases relate to pre-purchase eye examinations. The eye and sound vision are extremely important to any prospective owner and careful eye examination is of paramount importance. Many cases, in our opinion, prove to be normal variants but, unless the examining veterinary surgeon is very familiar with the normal variation of the equine eye, particularly in relation to coat colour and breed, difficulties may arise. For example, the eye may be apparently normal and “quiet”, but a change in iris colour may denote a previous bout of uveitis and therefore the probability of equine recurrent uveitis. Also, variations in the appearance of the fundus, both retina and optic nerve, and opacities in the lens, as well as pigment on the lens capsule indicating a previous uveitis, are all very important at a pre-purchase examination.
Neoplasia (tumours): This is a common tumour that we deal with on a regular basis. Unfortunately, there are some predisposing factors such as age and coat colour. Horses that are lacking pigment are more prone to SCC. In the early stages of the disease, it can mimic conjunctivitis and, unless a thorough search of the conjunctival sac is performed, the small tumour can be missed. Below are some presentations for SCC:
Surgical conditions: There are a large number of surgical conditions that benefit from immediate attention. Some of these are illustrated below:
- Iris prolapse as a result of a corneal injury. This was successfully treated by replacing the iris and putting a conjunctival graft into the area.
- A deep infected corneal ulcer that responded well to both appropriate medical and surgical treatment in the form of a conjunctival graft. The post operative picture shows a conjunctival graft placed into the defect to provide protection and healing. A lavage system is going through the upper lid. This allows for the automatic delivery of drugs very frequently with minimal intervention and stress to the patient.
Ocular Ultrasonography
Ocular ultrasonography can be performed in the conscious horse and is part of the routine ocular examination for some of our cases. It allows for a rapid and detailed examination of the globe and associated structures which is invaluable when an ophthalmoscopic examination is not possible due to opacity of ocular structures, as is corneal oedema or cataract formation.
