Cataract surgery in veterinary medicine today (Proceedings)
It is important to recognize qualities that affect candidacy for cataract surgery in our small animal patients. Although dogs more commonly have hereditary and diabetic cataracts than others domestic species, and so benefit from phacoemulsification lens extraction more often, potentially any species can benefit from cataract surgery. To warrant cataract extraction surgery, animal patients must have sufficient visual compromise to warrant taking a small risk of blindness from complications. However, it is a myth that cataracts need to "mature" before extraction. In fact, with today's technology, postoperative vision (with intraocular lens placement) can be expected to closely approximate "normal" barring significant complications and early cataract removal actually warrants an improved prognosis compared to removal of chronic cataracts in dogs.
Stable small (incipient) and early immature cataracts may not warrant removal, especially if the contralateral lens is clear, due to their less significant effect on vision. Late immature and mature cataracts are typically good candidates for extraction. It is highly beneficial for vision to remove hypermature cataracts, but postoperative risks are greater with removal of these advanced chronic cataracts. Nuclear lenticular sclerosis is a normal age-related cloudiness of the nuclear lens caused by continued deposition of cortical lens fibers over time, and which begins to become clinically noticeable around 8 years of age in the dog. Nuclear sclerosis is most easily diagnosed following pharmacological dilation as bilaterally symmetrical nuclear cloudiness surrounded by clear peripheral cortex. A fundic exam can be performed the through lens nucleus, which is cloudy, but not opaque. Only rarely do very advanced cases of nuclear sclerosis cause secondary changes (senile cataract) and visual compromise sufficient to warrant cataract surgery if the patient is healthy enough to safely undergo the necessary general anesthesia.
Although older and/or ill patients are not precluded from candidacy for surgery, it is important to remember that this is elective surgery. Any significant underlying systemic condition (diabetes mellitus, hypertension, Cushing's disease, renal insufficiency, heart disease, etc.), should be as accurately diagnosed and as well-controlled as possible prior to surgery and potential risks of general anesthesia discussed at length with the client. In fact, one of the most common indications for cataract extraction in canine patients is for the bilateral blinding mature cataracts that develop secondary to diabetes mellitus. In most cases, demonstration of adequate diabetic control (blood glucose curve or fructosamine) prior to surgery is indicated. That being said, some diabetic patients develop cataracts so rapidly that severe progressive lens swelling develops, which without rapid surgical intervention can lead to lens capsule rupture and/or development of glaucoma. In these cases, the luxury of waiting is lost and "emergency cataract surgery" may be indicated if there is to be hope of maintaining vision long-term.Positive clinical signs suggesting that cataract surgery will provide visual benefit include the presence of a strong dazzle reflex, strong direct and indirect pupillary responses, and presence of good vision before cataract development. Most veterinary ophthalmologists will require preoperative scotopic electroretinogram (ERG) and ocular ultrasound to confirm retinal function, often in combination with gonioscopy to evaluate iridocorneal (ICA) angle conformation. Animals that have low amplitude or "flat" ERGs, or retinal detachment usually are not candidates for cataract surgery. Those with significantly abnormally formed ICAs are at increased risk of postoperative glaucoma development, and although foreknowledge of this is useful, further client education is required before pursuing surgery.
In the lecturer's opinion, all small animal patients with advanced cataracts (but not those with lenticular sclerosis or incipient cataracts) should receive ongoing topical ant-inflammatory therapy even if anterior uveitis is not clinically evident. All significant cataracts have associated lens-induced uveitis (LIU) caused by leakage of lens protein through the lens capsule. Lens proteins are normally sequestered from the immune system, but cataract formation results in their leakage into the eye, and exposure to the immune system, which reacts to them similarly as to a foreign object. Uncontrolled LIU results in decreased surgical prognosis, so it is important to start treatment for LIU right away, even if surgery will be delayed. In fact, even low-grade uncontrolled LIU probably results in a cumulative risk of developing secondary glaucoma, so even if the clients would never consider cataract surgery, you should still treat. Aggressive treatment may be needed initially, followed by a taper to the lowest effective dose.