Cataract Surgery: Are We There Yet?

The short answer is, NO, we are not. The question that begs to be answered is, why not? The number of horses presenting for potential cataract surgery is very low, and the recent developments in equine cataract surgery are not widely available. Intraocular lens (IOL) replacement in the horse is in its infancy and is accompanied by a unique set of challenges which has proven to require different, or modified, instrumentation and surgical methods as the same procedure in dogs, cats and humans. (McMullen and Utter 2010; McMullen et al. 2010; Townsend et al. 2012)

Is an IOL necessary in the horse? Horses do not drive cars, nor do they read. They also seem to adjust well to unilateral and bilateral vision loss. The eye is an optical system, which can only function as intended if all of its components are present. If the lens were not necessary for the proper function of the eye, then it would not be present to begin with. Most horses undergoing cataract surgery have had to learn to live with severely compromised or absent vision. As a result, once the cataract is removed, the horse regains the ability to perceive the world around it, even without an IOL replacement. The aphakic globe is significantly hyperopic (far-sighted) and is not capable of focusing light onto the retina, which is essential for accurate image formation in the brain. Adaptation to hyperopia (far- sightedness), which is approximately +8.50 to +10.00 diopters in the horse, should not be equated with accurate vision. [...]