Corneal dystrophy in dogs – symptoms and treatment

Overview

The cornea protects the eye's internal structures and allows light to pass to the back of the eye. Dystrophy is a corneal change usually presumed to be inherited and initially developing without inflammation.

There are three main groups: epithelial, stromal and endothelial dystrophy. The names indicate which part of the cornea is mainly affected.

The epithelial form affects the surface cell layer, the stromal form the supporting tissue and the endothelial form the inner cell layer. Beneath the surface cells lies the basement membrane, to which the epithelium attaches.

The endothelium is a thin cell layer with Descemet's membrane immediately in front of it. Changes usually affect both eyes, but do not always develop at the same rate.

Corneal degeneration can look similar, although it results from another eye or systemic condition. A white patch may therefore be dystrophy or a secondary lipid deposit requiring different investigations.

Causes

Surface cells and lipid deposits

In epithelial dystrophy, cells may attach poorly to the underlying basement membrane. A poorly attached surface can break down repeatedly and heal slowly.

In the stromal form, lipids and other substances may accumulate in the cornea's supporting tissue. Lipid deposits often contain triglycerides and cholesterol.

These deposits can lie at different depths within the cornea. Macular dystrophy involves several pale, patchy stromal changes and more widespread cloudiness.

In the Labrador Retriever's macular form, the deposits consist of glycosaminoglycans, long sugar chains in the tissue. These lie between collagen fibres in the supporting tissue.

This Labrador Retriever form is associated with a CHST6 gene change identified in 2016. Inheritance is recessive: an affected dog needs the associated variant from both parents.

Disrupted fluid regulation by the endothelium

Endothelial cells regulate corneal fluid through active ion transport. Canine endothelial cells have limited ability to regenerate.

When too many cells are lost, fluid begins to accumulate in the cornea, causing oedema. Endothelial damage may involve dystrophy or age-related degeneration.

Severe swelling can form fluid-filled blisters on the corneal surface. Rupture of these blisters causes painful surface ulcers.

When is another condition responsible?

Secondary corneal deposits may involve inflammation or, for example, a disorder of blood lipid metabolism. Secondary lipid deposits can develop with dry eye, corneal inflammation or inflammation of the sclera.

Raised blood lipids may result from hypothyroidism, diabetes or Cushing's disease. Glaucoma, surgery inside the eye or lens instability can cause secondary endothelial damage.

Risk factors

Presumed inherited corneal dystrophies are recognised in about 20 breeds. Inheritance has been demonstrated in Beagles, Cavalier King Charles Spaniels and Siberian Huskies, for example.

Stromal dystrophy also occurs in Airedale Terriers, Cocker Spaniels, Bearded Collies, Samoyeds and Weimaraners. The stromal form is often found in young dogs.

Endothelial dystrophy mainly affects middle-aged and older dogs. Boston Terriers, Chihuahuas and Dachshunds are recognised risk groups.

Female Boston Terriers develop endothelial dystrophy more often than males. Affected females have an average age of about 7.5 years.

Severe stromal dystrophy affecting vision and causing pain also occurs in Shetland Sheepdogs. In a study published in 2019, signs of Labrador Retriever macular dystrophy were identified at 4.5–6 years of age.

Typical symptoms

Symptoms range from an almost unnoticeable white deposit to extensive cloudiness and painful ulceration.

• A white or grey patch is visible on the eye's surface.

• A silvery-grey or white deposit lies in the centre of the cornea.

• Cloudiness forms a ring near the corneal edge.

• Bluish cloudiness spreads from the outer edge towards the centre.

• Your dog squints or avoids bright light.

• The eye waters or produces mucus.

• The white of the eye reddens if ulcer-related irritation develops.

• Vision deteriorates if cloudiness covers much of the cornea.

Early endothelial disease may be difficult to see externally. Endothelial swelling can initially progress without pain.

Complications and consequences

The outlook depends on the affected corneal layer

Most dogs with dystrophy do not suffer substantial vision loss because of it. Superficial and many stromal findings usually have little effect on daily life.

However, macular patches can enlarge and become denser throughout the dog's life. This macular form can substantially impair vision.

As it progresses, macular dystrophy can also cause blood vessel growth into the cornea, although dystrophic findings usually have no vessels. Severe endothelial dystrophy can cloud the entire cornea.

An ulcerated cornea is susceptible to bacterial infection. A deep ulcer can perforate the cornea.

Corneal scarring may leave permanent cloudiness after healing.

Diagnosis at the vet

Location of cloudiness and other eye conditions

The vet assesses which corneal layer and area contain the cloudiness. A slit-lamp microscope allows examination of corneal structure and the front of the eye.

In cataracts, cloudiness lies in the lens inside the eye, rather than the cornea. Measuring tear production helps assess surface hydration.

Eye pressure is measured so that secondary damage, such as that associated with glaucoma, is not missed. Fluorescein staining identifies a corneal surface ulcer.

The dye adheres where protective surface cells are missing. A typical dystrophic deposit has no new blood vessels, while degeneration often involves vessel growth.

The examination also checks eyelid position and possible foreign bodies. If a lipid metabolism disorder is suspected, fasting cholesterol, triglycerides and glucose may be measured in blood.

Detailed investigations and inheritance

Corneal thickness can be measured with ultrasound to assess oedema. OCT imaging shows the different corneal layers and helps measure their thickness.

Confocal microscopy can assess endothelial cell shape and density. However, swelling can make the cells difficult to see.

Corneal photographs can be used to measure the area covered by oedema. Eye examination reports record the subtype separately to distinguish stromal, macular and endothelial forms.

A DNA test for macular dystrophy is available in some breeds. DNA testing does not replace examining the eye for other changes and different forms of dystrophy.

Some official eye screening schemes check the dog's identity before examination. The examination assesses structures including the lids, lens, vitreous and back of the eye as well as the cornea.

Treatment

Symptom-free deposits and surface ulcers

The vet prescribes medication and any procedures according to the eye examination. A stromal deposit that causes no symptoms or visual impairment does not usually need treatment.

A surface ulcer may require topical antibacterial medication. The vet may prescribe pain relief if needed.

A protective collar prevents further damage from rubbing. An uncomplicated corneal ulcer often heals within 3–5 days if ongoing irritation or infection does not delay healing.

However, repeated separation of surface cells associated with dystrophy can prolong healing. If abnormal eyelid position or a foreign body maintains an ulcer, that also needs correction for healing to occur.

A recurrent or deep ulcer may need treatment by a vet experienced in eye disease. For secondary lipid deposits, the underlying eye inflammation or condition raising blood cholesterol is treated.

Treating oedema in the endothelial form

Early oedema may be treated with a hyperosmotic eye preparation chosen by the vet. The aim is to relieve fluid accumulation and the symptoms it causes.

Severe cases may be considered for corneal thermal treatment or surgery using a conjunctival flap. Superficial keratectomy removes surface corneal tissue and may be combined with a conjunctival flap.

The benefit of these symptom-relieving operations may be temporary. In selected cases, transplantation of the whole cornea or its endothelial layer may be considered.

Corneal transplants are uncommon in dogs, partly because of donor tissue availability and complication risks.

What is known about new medicines?

ROCK inhibitors have been studied as a possible treatment for canine endothelial disease. A randomised netarsudil trial published in 2024 included 21 dogs.

Thirteen had endothelial dystrophy and eight had age-related endothelial degeneration. For the first four months, both owners and investigators were blinded to treatment allocation.

Netarsudil showed no clear benefit over placebo in corneal thickness, cell density or oedema. Only eyes with oedema affecting less than 40% of the cornea were included.

All dogs receiving netarsudil developed conjunctival redness at least once. However, this did not require stopping the medicine or separate treatment.

In addition, two dogs had persistently reduced tear production during medication and needed topical treatment affecting the immune response.

Prevention

Breeding choices and eye examinations are central to preventing inherited dystrophy. The breeding significance of a mild superficial or stromal finding is assessed according to the form and breed.

A dog with severe disease impairing vision or causing pain should not be used for breeding. Endothelial dystrophy is a reason not to breed from a dog.

A dog with macular dystrophy is also excluded from breeding. Simply removing a deposit or settling symptoms does not change the original inherited diagnosis to unaffected.

Important for dog owners

Some official eye screening schemes require a referral request to be arranged before the appointment.

Record which eye first became cloudy and whether the change has spread, because the eyes may differ.

Keep the eye examination report and information about which layer is affected. A similarly white-looking eye does not mean the same treatment or outlook for every dog.

New pain or squinting may indicate a surface ulcer in an eye that was previously painless.

The vet monitors healing of an ulcer receiving treatment through examinations.

At follow-up, ask whether the aim is to monitor a deposit, relieve swelling or treat an ulcer. Also explain whether medication is manageable at home and whether your dog's movement or ability to find objects has changed.

Frequently asked questions

Is corneal dystrophy always painful?

A mild stromal deposit is often free of inflammation and pain, so a white patch alone does not mean the eye hurts. However, breakdown of the corneal surface or rupture of oedema-related blisters in the endothelial form can cause severe pain requiring treatment.

Will a dog go blind from corneal dystrophy?

Most dogs retain vision, but the outlook depends on which corneal layer is affected. Severe endothelial dystrophy can cloud the entire cornea and cause painful ulceration, so it is monitored differently from a mild superficial deposit.

Does a white corneal deposit need medication?

A stromal deposit does not usually need treatment if it neither irritates the eye nor impairs vision. A painful corneal ulcer instead needs vet-prescribed treatment, which may include topical antibacterial medication and pain relief.

Can diet help with corneal cloudiness?

Diet changes may affect some degenerative corneal lipid deposits associated with blood lipid metabolism. This secondary degeneration is distinguished from true dystrophy during an eye examination, so treatment is not chosen by appearance alone for similar-looking cloudiness. Blood cholesterol and triglycerides are measured when necessary.

Is there a DNA test for corneal dystrophy?

DNA tests exist for some breed-specific forms of macular dystrophy, but different corneal changes are not the same disease. DNA testing does not replace a clinical eye examination assessing the affected layer, vision and possible other conditions. The Labrador Retriever's macular form has recessive inheritance.