Maria Kallberg, DVM, PhD, assistant professor at the University of Florida veterinary school, reported on cataracts in horses at the 2007 American Association of Equine Practitioners, held Dec. 1-5 in Orlando, Fla. She explained that a cataract is an opacity of the lens or lens capsule that obscures vision, as opposed to nuclear sclerosis, which is a normal aging process. She said congenital cataracts are usually bilateral (appearing in both eyes). Cataracts have been found to be heritable in Belgians, Morgans, Thoroughbreds, Rocky Mountain Horses, and Quarter Horses. In other instances, cataracts can develop secondary to trauma or due to chronic inflammation from uveitis (moon blindness).

Older horses with acquired cataracts that develop secondary to uveitis are not good surgical candidates due to the complication rate from post-surgical intraocular inflammation. Serious complications that can occur subsequent to this surgery include corneal ulcers, infection, membranous tags, and retinal detachment. Cataract surgery is most commonly performed on congenital cataracts in foals, with the ideal surgical candidate being one that is less than six months old, with no uveitis, and a healthy cornea and functional retina (based on tests explained by Dennis Brooks, DVM, PhD, Dipl. ACVO, a professor at the University of Florida). It is also important that a horse tolerates long-term therapy.

The method used to remove the lens is called phacoemulsification. A video was played demonstrating lens removal. A small slit is made in the edge of the eye near the conjunctiva, and the instrument emulsifies (breaks up into a suspension) the lens and aspirates the debris. The equine lens has a thick capsule that must be removed before the cataract-ridden lens can be retrieved from the eye. As yet, there is little experience in horses with replacing the cataractous lens with an artificial lens. Postoperatively, the horse will regain functional vision, but it will likely be far-sighted (not seeing well close-up).

Uveitis is the leading cause of blindness in the horse, with 50% of uveitis horses going blind with recurrent disease. Inflammation must be controlled before and after surgery with topical and systemic medications, and it is likely the horse will require lifelong therapy.

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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