One of the most common complications of diabetes in dogs is the development of cataracts, clouding over the lens of the eye. It is reported that approximately 75% of diabetic dogs will develop cataracts within 9 months of being diagnosed with diabetes, with blindness following as the cataracts mature. The formation of cataracts and following blindness may progress very quickly, although it is not entirely an irreversible process. With prompt management and treatment, the process can be delayed or even reversed.
What is happening to the eye?
The lens of the eye is protected by a capsule that receives nutrients from the surrounding fluids. One of the nutrients it uses is glucose. When glucose is in excess, what is not used by the lens is converted to sorbitol, a sugar alcohol, by an enzyme aldose reductase. Since sorbitol pulls fluid from the aqueous humor into the lens, the lens becomes swollen and lens fibers become degenerate, forming protein clumps over the lens. The lens clarity is disrupted and the structure is gradually deformed.
What happens when cataracts are left untreated?
There is a progression in clinical stages of cataracts, which is parallel to the increasing opacity of the lens. These stages are often divided into four: incipient, immature, mature, and hyper-mature. The incipient stage is the initial formation of the cataracts affecting <15% of the lens, while the immature stage is when the cataracts affects 15-100% of the lens, but is not thick enough to prevent the passing of light to the retina. The mature stage involves a 100%-affected lens and obstruction of light to the retina, which significantly reduces the dog’s ability to see. At this point, the entire lens will typically appear milky white. The hyper-mature stage is a very dangerous stage in which the lens undergoes spontaneous break-down and resorption, which is reflected in the glittery appearance of the eye. This stage is also characterized by wrinkling of the lens capsule because of the shrinking lens volume, and vulnerability to a cascade of problems, such as lens-induced uveitis (LIU), glaucoma, and retinal detachment.
Major complications of advanced cataracts:
- Lens-induced uveitis (LIU)
- When lens proteins are broken down and resorbed, they may leak out of the lens capsule. The immune system, hypersensitive to these leaked proteins, elicits an auto-immune response against them, inflaming the uveal tract of the eyes (iris, ciliary body, choroid). Signs of LIU in dogs may be squinting, excessively watery eyes, avoidance of bright lights, and in worse cases, bloodiness in the eye.
- Glaucoma is a serious condition in which the fluid pressure of the eye causes damage of the optic nerve. This can not only lead to permanent blindness, but is very painful. Symptoms of glaucoma are similar to LIU. Other signs may include swelling and/or bulging of the eyeball and no response to light.
What are the indications of cataracts?
- Cloudiness of the eyes (from bluish-gray to pearly whiteness and eventual glossiness)
- Behavioral changes that may hint vision loss (bumping into objects, difficulty in finding or locating objects, walking with hesitance)
- Change in blinking pattern or excessive tearing
What options of treatment are available?
Since cataracts may develop and mature very quickly in diabetic dogs, it is crucial for the affected dogs to be immediately seen by a veterinarian and given appropriate care as soon as symptoms show. If they are treated in the earlier stages, more options of treatment will be available and successful prognosis is likely to follow. For dogs with partial blindness, prevention of further vision loss may be enough since dogs are able to function without full visibility.
Surgeries are options in dogs with greater or complete vision loss. Phacoemulsification is a costly, yet a fairly common surgery method where the lens affected with cataracts is liquefied with sound waves and removed. It is usually followed by an artificial lens replacement. However, not all dogs will qualify for this procedure and so, each case will have to be individually evaluated pre-surgically. For example, glaucoma or retinal detachment will be complications that are likely to prevent an effective surgery. Topical medications may be supplemented for dogs with inflammation or high intraocular pressure.