Equine Eye Vets Veterinary Eye Care for Horses in Texas
Any opacity of the lens of the eye is referred to as a cataract. The lens of the eye is the structure inside the eye which allows animals to focus. Opacities may involve a small area of the lens or progress to involve the entire lens structure, in which case they can cause blindness in the affected eye. In some horses cataracts occur in only one eye – but in many cases both eyes are involved which may result in total blindness.
Many cataracts in horses develop associated with inflammation in the eye (equine recurrent uveitis). Some cataracts appear to be inherited and the genes for the disease are passed on from the parents. In most cases we do not yet understand what biochemical abnormalities the cataract genes cause and cannot prevent the disease from occurring in horses which inherit these genes.
At present there are no medications to remove cataracts. The only way to treat a dense cataract that is affecting vision is to surgically remove it from the eye. The most current technology for cataract removal (in people or animals) involves the use of phakoemulsification to remove the cataract. In this procedure an incision is made through the edge of the cornea (clear window at the front of the eye on which a contact lens would sit in a person). A hole is created in the anterior capsule of the lens to allow an ultrasonic probe to enter the lens and break up the cataract with ultrasound and then aspirate the emulsified lens contents from the eye, leaving behind only the lens capsule.
Contrary to popular belief there is no practical method yet available to remove a cataract with a laser (although a laser may be used after cataract surgery for residual opacities and scarring).
The normal lens provides a third of the power of the eye to focus light on the retina (the majority of the focusing power of the eye is from the cornea). When a cataract is removed the lens contribution is lost. To correct for this in people, dogs and cats at the time of surgery we replace the animal’s cataractous lens with a synthetic lens. Without this correction animals see better at a distance than they do close up. With a synthetic lens they have better near vision.
Early studies with hard intra-ocular lenses identified various problems with their implantation in horses (Millichamp and Dziezyc,1996). With research and development of new intra-ocular lens technology we can now implant foldable intra-ocular lenses in horses which should achieve more optimal correction of vision.
Cataract surgery is most likely to be successful in eyes where no other ocular or systemic diseases are present. If the eye is inflamed treatment with anti-inflammatory drugs is needed before surgery. If inflammation cannot be controlled (especially with equine recurrent uveitis) or high pressure (glaucoma) is present in the eye it may not be possible or sensible to remove cataracts. If retinal disease is present (degeneration or detachment of the retina) cataract surgery would not be recommended in most cases.
Before cataract surgery a thorough eye examination is always performed and most eyes undergo an ocular sonogram to enable us to see whether any retinal detachment is present. A test of retinal function called an electroretinogram (this tests retinal function in a manner similar to the way an electrocardiogram tests the function of the heart) may be performed in rare cases in horses before surgery.
Although many of the adults horses we see have a cataract in one eye only, younger animals may be affected in both eyes. For bilateral cataracts we usually operate one eye at a time with 1 - 3 weeks between the surgeries. In some cases a horse may go home after the first eye is operated and return some time later if the owner decides to have surgery on both eyes.
Using phakoemulsification we are able to restore useful vision in most horses. Just as with cataract surgery in people, a small percentage of horses may have complications associated with the surgery. The main problems encountered are inflammation (uveitis), which tends to be more severe in horses than in people and may result in scarring, which can affect vision. Some horses may develop increased intraocular pressure (glaucoma), which can cause blindness by damaging the optic nerve. Retinal detachment is occasionally seen as a complication of cataract surgery (just as in people). Infection in the eye, which fortunately occurs infrequently, can be a major complication – even resulting in loss of the eye.
Obviously as with any surgery there are risks associated with general anesthesia. At EEV we try to minimize these risks by performing blood tests and sometimes chest radiographs and umbilical ultrasonography (in foals) before surgery to detect any other systemic conditions which might affect the response to anesthetics or success of the surgery. If problems are detected we will recommend further workup before surgery. All patients are closely monitored during surgery and recovery.
Because we remove all of the contents of the lens it is not possible to again form a dense cataract. However some horses may have growth of a thin layer of lens cells over the remaining lens capsule after surgery which gives a hazy, gray appearance to the eye (posterior capsular opacification or PCO). In most cases this does not significantly interfere with vision.
It is very important that owners work closely with the veterinary ophthalmologist to ensure that their horse receive the best possible care after cataract surgery. After surgery the eyes are very delicate and have very fine sutures which close the incisions in the cornea. During the first few weeks several medications (usually eye drops) need to be applied up to four times daily to the operated eye(s). It is very important that these medications are applied to control inflammation and infection in the eye. Normally at EEV we hospitalize horses for a day or so before surgery and for 1- 4 weeks after surgery. We place a sub-palpebral lavage in the eyelid to enable easy administration of the topical eye medications. Horses are discharged when we feel that medication at home will be easily managed by the owners.
Equally important is the need to have frequent eye examinations after the surgery to ensure that all is healing well and that no complications are developing. If owners note any change in the eye after surgery they should not hesitate to contact the ophthalmologists. Some horses need some minimal amount of medication for several weeks after surgery.
Cataract treatment (workup, anesthesia, surgery) generally costs between $5500 to $9500 depending on whether one or both eyes need surgery and the duration and complexity of postoperative management. Medication costs vary depending on the length of time on medical therapy both before and after surgery. Development of any complications can extend the period of hospitalization and may require additional procedures and medications - this can affect the overall cost of the hospital stay.