Editor's Note: This article is part of TheHorse.com's ongoing coverage of topics presented at the 2012 American Association of Equine Practitioners' Focus on Ophthalmology conference, held Sept. 6-8 in Raleigh, N.C.
According to the National Eye Institute, more than half of Americans over the age of 80 suffer from cataracts, an ocular disorder characterized by opacity in the eye's lens. Similarly, many horses--from very young to very old--are affected by the same disorder. The difference? Cataract surgery to correct the problem is much more routinely employed in humans than in horses.
At the 2012 American Association of Equine Practitioners' Focus on Ophthalmology conference, held Sept. 6-8 in Raleigh, N.C., Brian C. Gilger, DVM, MS, Dipl. ACVO, professor of ophthalmology at the North Carolina State University College of Veterinary Medicine, discussed equine cataract surgery in-depth with the veterinary audience.
Gilger explained that cataracts, which were discussed more fully in a previous lecture at the conference, are relatively common in horses of all ages and are the most common congenital ocular anomaly in foals. Cataracts can also develop as horses age, or as the result of trauma or disease, he added.
While some cataracts cause few vision problems for horses, others substantially reduce their ability to see clearly and require surgical removal. The procedure of choice, Gilger said, is called phacoemulsification and aspiration (PA). He added that intraocular lenses have become common in cataract surgery as well.
Assessing Surgical Candidates
"We only take (surgical) cases that are really good candidates because this isn't an easy process," Gilger explained. Thus, prior to sending a horse to surgery, he recommends veterinarians perform a thorough ocular examination.
Gilger said that preoperative workups should include:
- A thorough examination of both eyes;
- A thorough physical examination (including a rectal exam to look for a predisposition to colic, he said);
- Complete bloodwork;
- An electroretinogram (which tests whether the retina is functional and, thus, if the horse has potential for sight); and
- An ocular ultrasound.
"Careful consideration should also be made of horses' and owners' temperament to determine if both can tolerate the long-term treatment and care that will be required after surgery," he added.
Preparing for Surgery
Gilger said veterinarians frequently employ systemic and topical antibiotics prior to surgery to reduce the risk of bacterial contamination and endophthalmitis (inflammation of the eye's internal structures) after the procedure's completion.
In the 24 hours leading up to surgery, he added, veterinarians administer intravenous antibiotics. Twelve to 18 hours prior to surgery veterinarians use topical atropine to dilate the horse's pupil, and they administer systemic non-steroidal anti-inflammatory drugs starting at least an hour before surgery, he said.
Additionally, many surgeons opt to use gastric protectants to reduce the risk of side effects, Gilger added.
Once the horse is ready for surgery, he is anesthetized and placed in lateral recumbency, Gilger said. He stressed that correct positioning is "critical for success" in ocular surgery, and he recommended a position that keeps the patient's cornea horizontal. To achieve this, the horse's nose is propped on foam pillows until it reaches the appropriate angle, he said.
He also noted that, to prevent facial nerve paralysis after surgery, the veterinary staff should remove the horse's halter and position pillows to avoid pressure on the animal's nerves.
He also recommended either paralyzing the horse or blocking nerves around the eye to prevent ocular movement and reduce pressure on the globes from muscles around the eye.
Gilger then reviewed surgical steps, intraocular lens placement, and surgical closure techniques with the veterinary audience.
Once a patient recovers from general anesthesia, his road to recovery begins. Gilger explained that veterinarians will be on the lookout for both short-term postoperative complications (including uveitis, corneal edema, blood in the eye, corneal dehiscence [failure of the healing incision], and retinal detachment) and longer term issues (including glaucoma, uveitis, corneal edema, capsular fibrosis [clouding over the lens capsule], and retinal detachment).
Immediately after surgery, veterinarians keep an eye out for colic, cecal impactions, colitis (inflammation of the colon), and laminitis, as these complications can sometimes prove fatal for patients, Gilger said. They also frequently administer postoperative for up to 12 hours following surgery, he added.
Many patients require medical therapy for up to three months following surgery, Gilger said, and some horses benefit from baseline doses of anti-inflammatories to help keep the affected eye(s) comfortable.
Many horses recover well from cataract surgery and retain vision in the affected eyes. Careful planning with a veterinarian and dedication to recovery efforts can help improve surgical outcomes.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.