Setting our Sights on Equine Glaucoma

What is glaucoma?
Horses eye
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Glaucoma in the most general sense refers to a group of eye conditions that can result in blindness (1). Medically speaking, it results from intraocular inflammation due to equine recurrent uveitis (eye inflammation). What happens is that the aqueous humor inside the eye becomes obstructed causing pressure within the eye to increase. The increased pressure leads to reduced blood flow from the retina to the optic nerve. Ultimately, the reduction in blood flow leads to cell death, compression of the optic nerve, and complete blindness (4)

How do I know if my horse has glaucoma?

Common symptoms of glaucoma include painful, red, or cloudy eyes. Horses commonly squint the eye closed (blepharospasm) or produce excess tears (epiphora). However, there is only so much that the eye itself can do to alert veterinarians about what is happening. Some horses don’t display any symptoms at all. This is why testing the intraocular pressure (IOP) is so critical to accurate diagnosis. Veterinarians use a special tool called an applanation tonometer which is a handheld device that measures IOP. If you’re curious if you can measure IOP yourself, the answer is probably not. In order to utilize the tonometer, the eye needs to first be anesthetized. This is probably for the best considering your horse is not likely to take well to you touching its eyeball (2).

What can be done to treat glaucoma?

Fortunately, glaucoma is a treatable disease, especially in its early stages. One such treatment includes using a drug called timolol. Timolol can lower IOP and delay eye deterioration for as long as three years (3). A more aggressive approach is laser surgery. Laser ciliary body ablation decreases the fluid produced by the eyes. This treatment requires sedation or anesthesia but can manage eye health for two to three years. While there are a variety of treatment options, none can prevent the inevitable, blindness. As glaucoma is a progressive disease it can only be managed, not treated (4). 

Horse corneal ulcer
A corneal ulcer stained green with florescence stain
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Given the brevity of this post, there is still more to learn about glaucoma. Check out the websites below to get a more detailed analysis of the issue at hand

Works Cited

  1. “Glaucoma.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 14 Nov. 2018, www.mayoclinic.org/diseases-conditions/glaucoma/symptoms-causes/syc-2037....
  2. Kane, Ed. “Treating Glaucoma in Your Equine Veterinary Patients.” dvm360, 30 June 2014, veterinarynews.dvm360.com/veterinary-treatment-glaucoma-your-equine-patients?id=&sk=&date=&pageID=2.
  3. “Timolol Eye Drops 0.5%.” Timolol Eye Drops 0.5% - Summary of Product Characteristics (SmPC) - (Emc), 24 Dec. 2015, www.medicines.org.uk/emc/product/4053/smpc.
  4. Tolar, Erica L, and Amber L Labelle. “American Association of Equine Practitioners.” How to Session: Ophthalmology , 2013, aaep.org/sites/default/files/issues/OphthalTolar.pdf.

This blog post was written by Caroline Treadwell, a senior in Animal Science and Biology.

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