Cataract Removal & Management
What is a cataract?
In health, light enters the eye and is focused by the cornea and lens to form an image on the retina.
The retina is a neurosensory membrane, capable of changing light information to neurological information. That information travels to the brain via the optic nerve in order for vision to occur. All the structures within the eye have to be living and metabolically active in order for intraocular structures to maintain health. Drainage of aqueous humor is vital to keep the intraocular pressures normal. A cataract is a result of death of a few or many of the lenticular cells resulting in a white opacity in the visual axis. A cataractous lens will reflect or refract light but will not focus it. An advanced cataract will result in vision impairment. Pets may maintain light/dark perception, even shadow vision, but will not be able to see clearly.
Why do cataracts form?
Most cataracts in dogs are caused by either an inherited defect in lens metabolism or by diabetes. The progression from the early (incipient) stages to advanced stages can take months to years in most cases. Some cataracts, particularly in diabetics, can progress very quickly, even within days.
How and why are cataracts treated?
As the cataract matures, lens proteins will leak through the capsular membrane that houses the lens. This lens protein is formerly unknown to the animals immune surveillance system and will cause inflammation called lens-induced uveitis. Lens-induced inflammation can be profound with rapid onset cataracts or it can be low grade with long standing cataracts. This concept is important because pre-operative lens inducted uveitis will influence both short and long term success rates. The window of opportunity for the most successful surgeries is dependent on the amount of preoperative inflammation.
When evaluating the animal eye as a potential cataract candidate, the veterinary ophthalmologist will evaluate the status of the cataract and associated inflammation, the position of the lens, the status of the retina and cornea and the anatomy of the iridocorneal angle and vitreous. With this information, the pros and cons of surgery are discussed in light of your particular situation.
Advances in patient selection and medical and surgical management of the cataract patient have influenced success rates that exceed 90% for the first year after surgery in an ideal patient. Factors that negatively influence success are weighed into the formula. (see complications handout). These include:
- Hypermature or long-standing cataracts, lens induced uveitis, or vitreous degeneration
- Statistically difficult breeds: Boston terrier, Bichon Frise, Cocker Spaniel, West Highland White, Schnauzer, Australian Shepherd, Brussels Griffon, Labrador Retriever
- Hypercholesterolemia or hypertrigleridemia (metabolic or diet related)
- Goniodysplasia, angle closure, or ciliary cleft collapse (factors that predispose or contribute to glaucoma)
- Intraoperative bleeding
The pros are obvious. Sight is a gift. Animals receiving an artificial lens recover full visual function after surgery. Patients that cannot receive replacement lenses recover functional vision within 3 weeks. Cataract surgery is the most successful option for animals to regain vision and avoid cataract-related complications (inflammation, lens luxation, glaucoma, retinal detachment). We remind clients, however, that animals that do not have cataract surgery may have excellent quality of life after an adjustment period so the commitment to surgery should be well thought out. Animals with the highest risk of complications are those that go without any medical or surgical treatment, so medical therapy in dogs that do not undergo surgery is strongly recommended.
The overall health of all animals should be thoroughly evaluated by the primary doctor prior to surgery. Blood work should be done at this time including a urinalysis (and urine culture in diabetic dogs). Urinary tract infections should be treated prior to surgery. It is also important to evaluate the teeth for tartar build-up and schedule a dental cleaning/prophylaxis prior to cataract surgery if indicated. Urinary tract infections, ear infections, and gingivitis are potential sources of bacteria that can enter the bloodstream and the eye at the time of surgery, causing a devastating ocular infection and loss of the eye.
The most current surgical technique (phacoemulsification) uses a probe that delivers ultrasonic waves to break up the lens. Surgery is often performed after electroretinography, a non-invasive electrical test to measure the retinal function. Anesthesia is closely monitored and complications from anesthesia are rare. During surgery, an artificial lens is placed after lens removal. Multiple eye drops are given three to six times daily for at least three to six weeks after surgery in routine cases and are necessary for a positive surgical outcome. Long-term use of topical anti-inflammatory eye drops daily or every other day is often necessary for long-term success.
What should I expect after surgery?
There are usually four to six post-operative rechecks during the first three months after the procedure. Canine and feline rechecks for three months are included in the cost of the procedure. Thereafter, it is generally recommended to have each patient evaluated every six to twelve months. Success rates drop by about five to seven percent per year due to undetected inflammation and associated complication of angle closure, retinal detachment and glaucoma. Poor night vision often occurs with time due to scarring around the old lens but day vision is typically maintained. Close post-operative surveillance and the use of topical or oral non-steroidals will minimize complications.