Cataracts in Dogs and Cats

TL;DR. Cataracts cause the lens of the eye to become cloudy, which can lead to blindness, but timely diagnosis and surgical treatment can successfully restore vision in many pets.

A cataract causes the normally clear lens of the eye to become cloudy and opaque.

What is it?

A cataract is a degenerative ophthalmic condition characterized by a loss of transparency in the lens of the eye. The lens is a normally clear, crystalline structure located behind the pupil that focuses light onto the retina at the back of the eye. This structure is held in place by delicate suspensory tissues, as described in a leading veterinary anatomy reference:

"The zonular fibers, which suspend the lens, insert into the superficial layers of the lens capsule. More and larger fibers insert in the thicker anterior capsule than on the posterior surface (see section on zonule) . The lens rests in a depression in the vitreous, the hyaloid fossa ( Fig. 21. 20) . The vitreous is tightly adherent to the posterior capsule."

When cataracts develop, changes in the solubility of lens proteins cause the lens to lose its clarity, gradually turning cloudy, milky, or opaque. This opacity blocks light from reaching the retina, resulting in progressive vision loss and, eventually, complete blindness.

In metabolic disorders such as diabetes mellitus, cataracts can develop rapidly due to osmotic changes. High levels of glucose in the blood spill over into the fluids of the eye. This excess sugar is converted into sorbitol, which draws water into the lens. This sudden influx of water causes the lens fibers to swell and rupture, a process known as lens intumescence. This rapid swelling can lead to severe internal inflammation and may even cause the outer capsule of the lens to rupture.

Causes & risk factors

Cataracts are common in both dogs and cats, though their underlying causes can vary. The primary risk factors and triggers include:

• Age-related degeneration: Over time, the proteins within the lens can naturally degrade and clump together, leading to senile cataracts.
• Metabolic disorders: Diabetes mellitus is a major cause of rapid cataract development, particularly in dogs. Fluctuating blood sugar levels significantly accelerate this process. As noted in a prominent veterinary internal medicine textbook:

"Cataract formation is an irreversible process once it begins, and it can occur rapidly. Diabetic dogs that are poorly controlled and have problems with wide fluctuations in blood glucose concentrations seem especially at risk for rapid development of cataracts."

• Secondary inflammation: Chronic internal eye inflammation (uveitis) is a frequent cause of cataracts, especially in cats.
• Trauma: Penetrating injuries to the eye can damage the lens capsule, leading to localized or complete cataract formation.

While some species-specific genetic pathways exist, no specific breed predispositions are detailed in the clinical record for this condition.

Signs to watch for

Cataracts can progress at different rates depending on their cause. Owners should watch for the following clinical signs:

• Loss of lens transparency (Cardinal): A visible cloudy, grey, blue, or white reflection inside your pet's pupil.
• Blindness (Common): Bumping into walls or furniture, hesitation in low-light environments, or reluctance to jump onto surfaces.
• Lens-induced uveitis (Common): Internal inflammation of the eye caused by leaking lens proteins. This presents as redness in the white of the eye, squinting, or watery discharge.
• Lens swelling or intumescence (Occasional): The lens physically enlarges due to water influx, most commonly seen in diabetic pets.
• Reduced depth of the anterior chamber (Occasional): As the lens swells, it pushes the iris forward, narrowing the space in the front of the eye.
• Capsular rupture (Occasional): The outer membrane of the lens tears under pressure, releasing highly inflammatory proteins into the eye.

Cats can also develop cataracts, often accompanied by signs of internal eye inflammation.

How vets diagnose it

Your vet will perform a comprehensive ophthalmic examination to differentiate cataracts from nuclear sclerosis, a normal aging change where the lens appears cloudy but remains transparent to light.

To determine the exact stage of the cataract, your vet will classify its progression based on how much of the lens volume is affected. As outlined in a leading veterinary imaging reference:

"The classification based on the stage of progression of the cataract is clinically more useful and includes incipient, immature and mature cataract with < 10% of the volume, 10–100% of the volume with partial opacity, and 100% complete opacity, respectively. These stages usually maintain the lens volume which instead may be increased in diabetic mature hyperosmotic cataracts (intumescent)."

If the cataract is mature and completely blocks the vet's view of the back of the eye, advanced diagnostic tests are required:

• Ocular ultrasonography: This non-invasive scan allows the vet to evaluate the structures behind the cloudy lens, checking for retinal detachment or lens resorption. As noted in veterinary ultrasound literature:

"Resorption can be detected as a decrease in the antero-posterior width of the lens and an increased depth of the anterior chamber."

• Electroretinography (ERG): This test evaluates the electrical activity of the retina. It is essential before considering surgery, as it confirms whether the retina is healthy enough to support vision once the cataract is removed.

Ocular ultrasonography allows veterinarians to evaluate the structures behind an opaque lens.

Treatment options

Once cataract formation begins, the process is irreversible. Medical treatments cannot dissolve a cataract, but they are vital for managing secondary complications. Surgery remains the gold standard for restoring vision.

Surgical Therapy

Surgical removal of the lens (typically via phacoemulsification) is the only definitive cure for cataracts. During this procedure, the cloudy lens is broken up with ultrasonic waves and removed, often replaced with an artificial intraocular lens. Vision is restored in approximately 80% of diabetic dogs that undergo cataract surgery. However, long-term success depends heavily on strict glycemic control, overall retinal health, and the management of pre-existing lens-induced uveitis.

Medical Management

If surgery is not an option due to concurrent health issues or financial constraints, medical therapy is directed at controlling pain and inflammation:

• Glucocorticoids (Corticosteroids): Topical anti-inflammatory eye drops are prescribed as a first-line therapy to control lens-induced uveitis. These drops help prevent secondary complications like glaucoma (increased pressure within the eye).
• Hyaluronate Sodium (Mucopolysaccharide / Joint Protectant): This is utilized as a supportive ophthalmic agent, often during surgical procedures, to protect delicate ocular tissues and maintain lubrication.

Prognosis

For pets undergoing surgical cataract removal, the prognosis for restoring functional vision is good, with an approximate 80% success rate in diabetic dogs.

If surgery is not performed, the long-term prognosis for vision is poor, resulting in permanent blindness. However, many blind pets can still maintain a high quality of life in a stable, safe environment. In these cases, lifelong medical management with anti-inflammatory eye drops is often required to prevent painful secondary conditions like glaucoma or lens rupture.

Prevention

Because many cataracts are degenerative or genetic, they cannot be entirely prevented. However, for diabetic pets, strict management of the disease is crucial. Maintaining stable blood glucose levels through consistent insulin therapy, routine veterinary monitoring, and a controlled diet can help prevent or delay the rapid onset of diabetic cataracts.

Regular veterinary exams are the best way to detect cataracts early, allowing you to manage inflammation before it causes irreversible damage to the eye.

When to call your vet

Contact your veterinarian if you notice any cloudiness in your pet's eyes, changes in their vision, or if they begin bumping into objects.

Seek immediate emergency veterinary care if your pet shows signs of severe eye pain, such as keeping the eye squinted or closed, pawing at their face, or if you notice sudden redness in the white of the eye. These signs can indicate acute complications like lens rupture, severe uveitis, or glaucoma, which require urgent medical intervention to save the eye.

Sources

• Atlas of Small Animal Ultrasonography, 2nd Edition, p. 47
• Internal Medicine, 5th Edition, p. 831
• Miller and Evans Anatomy of the Dog, 5th Edition, p. 1725