November is Pet Diabetes Month, making this a good time to discuss how diabetes can affect your pet’s eyes. Complications in diabetic dogs frequently include cataracts and retinopathy. Our Veterinary Vision Center team would like to provide information about how these conditions can affect your dog and how they are managed.

Diabete mellitus in dogs

Glucose is broken down from starches and sugars in the diet to provide fuel for cells. Insulin, which is produced by the pancreas, is required for glucose absorption. Without insulin, glucose remains in the bloodstream and cannot be used by the body. The most common form of diabetes in dogs is insulin-deficient diabetes, which occurs when the pancreas is damaged or not functioning properly, and insulin production is inadequate. Insulin-resistant diabetes is another form in which the pancreas produces insulin, but the cells don’t respond normally to use the glucose.

Additional details about diabetes include:

  • Negative effects — Cells in the dog’s body are deprived of fuel they need for energy, and the body breaks down fat and proteins to use as alternative fuel sources. In addition, high blood glucose levels can damage many organs, including the kidneys, heart, eyes, blood vessels, and nerves.
  • Signs — Early signs are commonly increased thirst and urination, increased appetite, and weight loss.
  • Diagnosis — Diagnosis is made when elevated glucose levels are detected in your dog’s blood and urine.
  • Treatment — Treatment typically involves a diet change, a consistent exercise routine, daily insulin shots, and close glucose monitoring.

Diabetic cataracts in dogs

Diabetic dogs frequently develop cataracts—approximately 50% develop cataracts within five months of diagnosis, 75% within one year, and 80% within 16 months. Details about diabetic cataracts in dogs include:

  • Cataract development in diabetic dogs — The lens does not receive a direct blood supply and relies on eye fluids for nutrients. Normally, the lens absorbs glucose from the eye fluids, using most of the glucose for energy needs, and converting the remainder to another sugar, called sorbitol. Diabetic dogs have excess glucose in their eye fluids, and produce excess sorbitol, which pulls water into the lens, disrupts the lens clarity, and causes cataract formation. Typically, diabetic cataracts start at the lens periphery but quickly mature to involve the entire lens. Cataract formation does not imply poor diabetic control, since well controlled diabetic dogs also can get cataracts.
  • Lens induced uveitis — Uveitis occurs when the lens absorbs water and swells, and lens proteins leak from the capsule, inflaming the eye’s vascular tissue. Uveitis must be treated aggressively to prevent complications such as lens luxation, secondary glaucoma, and retinal detachment. Signs include squinting, tearing, conjunctival redness, and pupil constriction. 
  • Medical management — Topical nonsteroidal anti-inflammatories (NSAIDs) should be initiated as soon as cataract formation is recognized to help prevent lens-induced uveitis. If lens-induced uveitis is present, systemic NSAIDs can help control the inflammation and pain, and topical medications can maintain pupil dilation. Topical steroids may be recommended, but these medications can be systemically absorbed and dysregulate the dog’s diabetes.
  • Surgical management — Cataract surgery to remove the lens is the only way to restore vision and is considered the gold standard approach. Reported success rates are around 90% to 95% in most dogs. If the cataract is the only eye abnormality, and the dog’s diabetes mellitus is well regulated, the cataract can be surgically removed and replaced with an artificial lens. If the eye is significantly affected by lens-induced uveitis or otherwise damaged, vision may not be salvageable.

A veterinary ophthalmologist should determine if cataract surgery is feasible for your diabetic dog. Our Veterinary Vision Center team will check your dog’s eye for uveitis and perform an electroretinogram (ERG) to test your dog’s retina for electrical activity, to ensure the cataract surgery will not destroy their vision. Dogs who undergo cataract surgery are monitored long term and typically maintained on topical NSAIDs. 

Diabetic retinopathy in dogs

High blood glucose levels can damage the blood vessels that provide nutrients to the light-sensitive tissue at the back of the eye (i.e., retina). Diabetic retinopathy is not as common in diabetic dogs as in humans, but does occur. The condition progresses in two stages:

  • Non-proliferative diabetic retinopathy — Tiny blood vessels that are damaged begin to leak, and the retina swells. In addition, the blood vessels that support the retina can be obstructed, closing off blood supply to the retina.
  • Proliferative diabetic retinopathy — In a process called neovascularization, the retina starts growing new blood vessels, and these fragile new vessels bleed into the eye, obstructing vision, and can form scar tissue, leading to retinal detachment. Glaucoma is also a potential complication if the new blood vessels interfere with the normal flow of fluid from the eye, causing increased eye pressure. 

Controlling your dog’s diabetes is the best way to manage and potentially prevent diabetic retinopathy. Anti-inflammatory medications may be prescribed for diabetic dogs, and treatments to address complications such as retinal detachment and glaucoma may also be necessary.

Detecting diabetic ocular issues in the early stages is important for devising an appropriate management strategy. If your dog has diabetes, contact our Veterinary Vision Center team, so we can determine if they have diabetic cataracts or retinopathy and develop a plan to preserve their vision.