by William W. Miller, DVM, MS, DACVO
IEOC PR Committee Chair

Should my horse have cataract surgery?
Clients often ask about cataract surgery for their horse. In the recent Veterinary Ophthalmology special equine edition Brooks, et. al. reported restoration of vision in operated horses 87.3% at less than one month and 26.3% visual greater than 24 months. In that same article the authors state, ’Problems do remain, however, and some veterinarians feel it is unethical to recommend that horses with cataracts, or horses that have had cataract surgery are safe to ride.’ To begin to reach a consensus within our group the opinion of our members who are avid equestrians and trained scientists were asked their thoughts on the subject of cataract surgery in horses. Emails were sent to many IEOC members seeking their input. The following are responses from two members for which the IEOC newsletter is very grateful.

Dr. Marjorie Neaderland, DVM, DACVO:
I practice equine veterinary ophthalmology in the Northeastern United States, specifically Connecticut and Southern New York. The horses I am involved with professionally and personally are performance sport horses, typically warm bloods and thoroughbred crosses used for showing as hunters, jumpers and dressage. Polo is another popular sport in my area. There are also a significant number of pleasure horses used for trail riding. Those horses are generally warm bloods, draft mixes, thoroughbreds and Icelandic horses. I am an avid rider personally, doubling as a veterinary ophthalmologist to support my horse in the manner he has become accustomed to.

Vision impairing cataracts have rarely been seen in my clinical practice of 24 years. Uveitis being the predominant cause of unilateral cataract or sight impairing intraocular changes but I recently have had two horses presenting to me prompting the consideration of cataract surgery.
 
The first horse was an attractive four year old warm blood sport horse gelding acquired for training and sale as a high end jumper. He was in full training demonstrating athletic prowess in his intended occupation, free jumping large fences and beautiful natural gaits under saddle. He had recently sustained trauma of unknown origin to the right side of his head in the pasture which led to a transient uveitis and a focal tear in the axial anterior lens capsule resulting in an intumescent mature cataract with extrusion of cataractous lens fibers through the lens capsule tear into the anterior chamber within six months of the injury. An unfortunate freak occurrence to be sure, but a decision regarding the fate of that eye needed immediate consideration. My opinion was that without surgical intervention, phacoclastic uveitis would occur leading to a painful blind eye with enucleation or evisceration/implant resulting. Either of those surgeries would certainly make the horse comfortable but would make him significantly less attractive for sale. I do not generally consider cataract surgery an emergency procedure but this case was an exception. My conversation with owner was directed at long term comfort of the horse, usefulness of the horse in his anticipated athletic career and future sale/value of the horse.
 
There have been two recent articles in Veterinary Ophthalmology journal describing relatively large populations of post-operative equine phacoemulsification surgery results out of North Carolina State (Edelmann, 55 eyes) and University of Florida, Gainesville (Brooks, 111 eyes), coming out of leading institutions in the equine cataract surgery field, citing relatively favorable long term visual successes for aphakic and pseudophakic post-op phacoemulsified eyes.
 
The discussion of effects of cataract surgery on equine vision, with or without IOL implantation is beyond the scope of this newsletter posting, but given an appropriately designed and placed IOL without the numerous possible intra-op, peri-op and post-op complications, an IOL should improve functional vision and that would be the ultimate goal of removal of the cataract. I strongly recommended referral of this equine patient for cataract surgery at one of the above cited institutions, which was done post haste, an IOL was placed, with a great surgical outcome to date. Now about six months post-op, the horse is back in jumping training with the experienced trainers who have not appreciated visual issues they can ascribe to the surgical eye.
 
The next horse I was called upon to examine for a recommendation for cataract surgery was a 14 year old low goal polo pony mare. The owner had noticed gradual clouding of both eyes. She had not appreciated a decrease in vision affecting the performance in her game. Exam revealed both eyes to have extremely dense nuclear sclerosis and dense immature cataracts with neither retina visible even with fully (Tropicamide) dilated pupils. There was no evidence of uveitis present in either eye. The horse was unable to walk over ground poles placed in a line before him without tripping, demonstrating severe vision impairment. The owner was completely surprised by this revelation of how poor her vision actually was but was already emotionally prepared to have cataract surgery performed to safely return her horse to the game. In this case, the cataracts rendered this polo pony unsuitable for its intended purpose. This horse recently had unilateral cataract surgery but has not yet returned to her stable for her post-op recheck.
 
There are certainly well founded questions about the pros and cons of equine cataract surgery. The reported results of the above mentioned papers, with “vision” loosely defined, state 54% visual at 35 months (Edelmann) and 26.3% visual >24 months post operatively (Brooks), which compared to MD phacoemulsification reported results is poor but loss of cases for followup continue to plague our veterinary results. Years ago I examined an Olympic level dressage horse that was performing beautifully with almost mature cataracts. There are numerous YouTube videos of blind horses performing their tasks, leading satisfying productive lives with their riders. The decision to pursue cataract surgery is multifactorial, based on the individual situation, personality of the horse, horse and rider combination, financial and logistical considerations. Safety of horse and rider have to be a prime factor in our litigious society.
 
Dr. Susan Keil, DVM, DACVO: 
I would encourage a client to pursue bilateral cataract surgery with lens implantation on their competitive horse, those competing in stadium jumping and cross-country courses. (Note: the specific parameters leading up to this recommendation include a horse that is an excellent surgical candidate, an educated client with unlimited financial resources, a previously trained horse, and a competent rider. I feel this surgery would have the potential to help the client, the horse, and our ophthalmology community.)
 
My rationale for this response evolves from working with both professional trainers and competitive amateurs of many disciplines as well as my personal horse ownership and competition experiences. When I diagnose cataracts in any horse, the obligatory discussion concerning financial, legal, ethical, and philosophical factors always occurs. Covering these issues thoroughly is something all of us have been professionally trained to do. What I actually find more insightful, though, is what the horses have taught me. From a rider’s viewpoint, my personal horses have taught me to rethink vision, abilities, and trust. Also, I know more than one rider currently jumping functionally monocular sighted horses greater than 3’6. These animals are doing well competitively and these riders feel comfortable. I appreciate monocular vision is not the same as our post-op cataract scenario, but I envision a successful post-op patient would have either improved function (compared with monocular) or be uniquely visually challenged (as the monocular horse is).
 
I have too many horses (6), currently ages six to 26. I’ve competed in endurance riding (25 to 100 miles distances) for 15 years. I have thousands of hours in saddle, often trotting and cantering, through very uncontrolled environments. The reliability, safety, and trust I feel with each horse are inversely proportional to their age. The significance here is my oldest, Shaikh, lost his right eye (glaucoma) two years ago, yet I still feel most completely comfortable on his back. I don’t ride him nearly as often now because of his age (and too many others to ride), not because of his monocular vision. Yes, I have to ride him from a different perspective (meaning I account for his deficit field and lack of depth perception), but this was an easy transition with a few rides because of our years of teamwork. Any horse’s mental maturity and experience are huge factors for me. It would take years of training and a large financial investment to find another Shaikh. These same factors also hold true for in hand/on the ground safety and trust issues. 
 
Searching for a horse with specific competitive abilities can actually be mentally exhausting and financially bruising. To replace the competitive talent and experience of the horse with the cataracts can literally take months to years to find one within the budget (and the budgets are often impressive) that passes the vet check and has the correct personality. The cost of cataract surgery may be a significantly wiser investment countered against the factors of searching, vet checks, travel for evaluations, horse transport, developing team savvy, and months to years of training. 
 
The other tangible factor goes back to the horse-human bond. I love my horses. I for one would want to “fix” my horse, not replace him. Why would I not want to help my friend improve his quality of life? That would be great! Now, I could be up for the discussion of an additional horse…