Glaucomas

Glaucomas refer to a group of ocular diseases that result from alterations in the formation and drainage of the aqueous humor, which is the fluid that is located in the space in front of the iris and lens. One of the most notable results is increased intraocular pressure. The pressure increases due to a decrease in the natural outflow of the aqueous humor. This fluid is not only important for providing nutrition to the cornea and lens, but is also critical for the optimal arrangement of the eye. The optic disk, which is located in the back of the eye, is the connection between the eye and the brain, and therefore can be damaged when the pressure within the eye remains elevated for prolonged periods of time. This can result in blindness.

Equine glaucoma can be divided into three categories, including primary, secondary, and congenital types.

1. Primary glaucoma is generally associated with biochemical alterations of the internal structure of the eye. The changes in this category may not be visible.
2. Secondary glaucoma, also common in horses, has several identifiable characteristics such as uveitis, iris and ciliary body tumors, and lens dislocation. In these cases the aqueous humor drainage pathways commonly get clogged with inflammatory debris, tumor cells, or lens material, causing increase pressure.
3. Congenital glaucoma, which is mostly reported in foals, can be associated with developmental abnormalities. 

​In general, most cases of glaucoma are seen in horses with recurrent uveitis, which is inflammation of the uvea (the middle layer of the eye between the retina and the whites of the eye). Horses older than 15, and Appaloosas have higher prevalence of uveitis. Recognition of subtle clinical signs help to catch glaucoma in early stages. 
 
Clinical Signs:
- enlarged globe
- cloudiness of the cornea
- small white streaks within the cornea (stria)
- vision deficit, small pupils, corneal edema
- squinting of the eye
- increased discharge
- increased redness around the margins of the globe.
 
A great aid in diagnosing glaucoma is through the use of an instrument called a tonometer. This tool helps to measure intraocular pressure of the eye. Normal intraocular pressure is between 17 and 28 mmHg. An increased intraocular pressure is defined as glaucoma. Starwood Equine is proud to provide our clients with access to earlier diagnosis and treatment with the use of this instrument.

Treatment of glaucoma can vary based on the primary cause of the disease and the horse’s level of vision. The goal of treatment is centered around increasing the flow of fluid within the eye. There are several medical options for treatment, including Timolol and Dorzulamide, and non-steroidal anti-inflammatory drugs such as Banamine. If medical avenues do not solve the problem, there are other options such as cyclophotoablation; a procedure in which a laser is used to destroy the ciliary body, which is the structure in the eye that produces fluid.

ENUCLEATION

Lastly, if the animal is blind and painful as a result of glaucoma, enucleation is an option for long lasting pain relief. Starwood Equine, offers standing enucleations for patients that require a more permanent pain relief. Our patients are able to stay in the comfort of their own barn while this procedure takes place, helping to minimize stress levels. Our veterinarians start by heavily sedating the patient. They then proceed to numb around the eye with a series of nerve blocks. Next, doctors carefully dissect the tissue surrounding the eye, allowing it to become freed for removal. Once removed, doctors take out any remaining ocular tissue, the area will appear as if the eye is just closed with the eye still inside. As the healing process continues, the area will become more concave. The estimated recovery time is about two weeks. ​

Enucleation is the removal of the eye that leaves the eye muscles and remaining orbital contents intact. This is one of the most frequently performed orbital surgeries in equine medicine and often horses are able to return to work.

In fact, you may recall a one-eyed racehorse, Patch, competing in the 2017 Kentucky Derby.

(Michael Reaves / Getty Images)