Corneal ulcers in dogs: damage to the eye's surface

Overview

The cornea lets light into the eye. It also forms a strong barrier between the eye and the environment. Its outermost cell covering is called the epithelium. Beneath this, the stroma, or connective tissue layer, makes up around 90% of corneal thickness. Deeper still are the thin Descemet's membrane and the endothelial cells lining the inner surface.

A superficial ulcer involves a break in the surface cells. A deep ulcer extends into the supporting connective tissue layer. In a descemetocele, this layer has been lost down to Descemet's membrane.

The transparency of the corneal stroma depends partly on the regular arrangement of collagen fibres. The inner endothelium regulates corneal fluid content by pumping water into the anterior chamber. Nerve endings from a branch of the trigeminal nerve provide corneal sensation.

In England in 2013, 104,233 dogs were followed at 110 veterinary practices.

Corneal ulcerative disease was diagnosed in 834 of them. The proportion diagnosed during the year was 0.80%. This figure describes dogs receiving primary veterinary care in England.

Causes

Most canine corneal ulcers begin with mechanical injury. A stick striking the eye can break its surface. A scratch from another animal's claw can also cause an ulcer. Injury can also occur when a dog rubs the eye on a carpet.

Low tear production predisposes the eye's surface to damage. An inward-turning eyelid can rub the cornea. Eyelashes growing in the wrong place can maintain similar irritation. An irritating chemical entering the eye, such as shampoo, can cause chemical injury.

A break in the surface layer allows bacteria into deeper tissue. Enzymes from microbes and damaged tissue can break down the connective tissue layer. This tissue breakdown is called corneal melting.

In an indolent, or poorly healing, superficial ulcer, new epithelial cells do not attach properly to the underlying tissue. An abnormal hyaline layer beneath the surface cells can prevent attachment. Such an ulcer can develop without a known injury.

Without secondary infection, an indolent ulcer stays superficial and does not damage the underlying stroma.

Facial nerve paralysis may underlie a poorly healing corneal lesion. Corneal degeneration can also interfere with ulcer closure.

Risk factors

Short-muzzled dogs are more prone to corneal ulcers. In the 2013 English figures, the annual proportion in Pugs was 5.42%. In Boxers, it was 4.98%. These proportions cover all diagnosed forms of corneal ulcerative disease.

Indolent ulcers occur particularly in middle-aged and older dogs. The average age of dogs with this ulcer type is seven to nine years. Boxers are particularly common among dogs with indolent ulcers. However, the condition also occurs in other breeds and crossbreeds.

No clear sex predisposition has been established for indolent ulcers. In dogs with dry eye, bacterial inflammation can destroy the corneal stroma particularly readily.

Typical symptoms

A corneal ulcer is usually a very painful eye condition. However, a small superficial lesion may be invisible to the naked eye.

• Squinting: the dog tightly closes the eyelids to protect the painful eye.
• Rubbing: the dog tries to relieve pain with a paw or by rubbing the eye on a carpet.
• Tearing: more clear fluid than usual flows from the eye.
• Discharge: mucus may collect at the corner of the eye.
• Redness: the conjunctiva covering the white of the eye may look red.
• Cloudiness: the previously clear cornea may become cloudy.

Small blood vessels may grow over the corneal surface alongside an ulcer. A dense white deposit at the ulcer margin may suggest bacterial involvement.

Discharge may run from the corner of the eye into the facial hair. Conjunctival swelling can also make the eye look irritated.

Complications and consequences

Even a superficial ulcer can deepen despite treatment. A persistent indolent ulcer can cause corneal pigmentation. An untreated or incorrectly treated indolent ulcer can persist for weeks or months. A deepening lesion can perforate the cornea.

Perforation allows fluid from inside the eye to leak out. A severe ulcer can cause permanent loss of sight. It may also be associated with inflammation inside the front of the eye, called anterior uveitis. Surgery may leave a visible corneal scar.

Adhesions can form inside the eye after surgery for a deep ulcer. Secondary cataract is another possible consequence of surgery. An ulcer in the centre of the cornea is vulnerable because blood vessels supporting healing take longer to reach it.

Following conjunctival grafting for a deep ulcer, healing has been estimated in 85–90% of cases. Graft failure is also a possible complication. Extensive corneal blood vessels can interfere with vision even after ulcer closure.

Diagnosis at the vet

The vet examines the eye's surface with fluorescein dye. The dye adheres where the protective epithelial covering is missing. The lesion appears green under cobalt-blue light. Assessing depth requires magnification and focused light.

A Schirmer tear test measures tear production. The examination also looks for foreign bodies and eyelid defects rubbing the eye's surface. Poorly healing ulcers warrant investigation of corneal and nerve function disorders too. A Seidel test can check for fluid leaking from inside the eye through a perforation.

Cell sampling and bacterial culture are recommended for an infected ulcer before topical antibiotics begin. Susceptibility testing helps select treatment effective against the bacteria. In an indolent ulcer, dye spreads beneath the loose epithelial edge, forming a paler halo. Diagnosing an indolent ulcer requires investigation of other factors preventing healing.

Assessment considers when the ulcer began, as well as its location and depth. Samples from a persistent or deep ulcer may be taken before dye is applied. Follow-up checks monitor healing partly through a reduction in the area taking up dye.

Treatment

Superficial ulcers and monitoring

The vet chooses treatment according to ulcer depth and severity. An ordinary superficial ulcer is usually treated medically. A topical antibiotic helps prevent bacterial infection of the damaged surface. Oral pain relief can ease eye pain.

A medicine that dilates the pupil can reduce pain caused by muscles inside the eye. Any underlying cause damaging the surface must also be corrected. An uncomplicated superficial ulcer usually heals in three to five days. Renewing the epithelial covering over the entire corneal surface takes around four to seven days.

Building the new surface cells' basement membrane and firm attachment takes longer. A healing timeframe of 7–14 days is also used for superficial ulcers. Persistent ulcers prompt investigation for factors such as dry eye or mechanical irritation. The first follow-up is often only two to three days after treatment starts.

Treating a poorly healing superficial ulcer

An indolent ulcer is also called an SCCED. A topical antibiotic alone does not usually heal this type of ulcer. The vet removes poorly attached epithelium after applying local anaesthetic to the eye. Debridement with a cotton bud alone heals around 20–84% of indolent ulcers, averaging around 50%.

These results include different numbers of procedures and supportive treatments. Diamond burr debridement also treats the altered superficial connective tissue layer. A single diamond burr treatment has healed 77.4–92.5% of indolent ulcers. An alternative, grid keratotomy, involves making a superficial grid pattern over the ulcer area.

A single grid keratotomy has healed 75–100% of patients with indolent ulcers. Similar mechanical surface treatment is unsuitable for a deep corneal ulcer because of the risk of perforation. A bandage contact lens can protect exposed nerve endings and improve comfort after the procedure. Bacterial inflammation must be excluded before a bandage contact lens is used.

A bandage contact lens has shortened healing of an indolent ulcer by around three days. Follow-up after SCCED treatment is usually at 10–14 days. A difficult recurrent ulcer may need more than one treatment. An indolent ulcer that does not heal with other methods can be treated by surgically removing the affected surface.

Superficial keratectomy is a microsurgical procedure in which the affected area is removed under general anaesthesia. It is not the first-choice treatment for an indolent ulcer.

Deep or infected ulcers

An infected ulcer needs effective treatment to stop tissue destruction. Serum or other topical protease inhibitors can limit corneal melting. The first check of an infected ulcer may be needed within 24–72 hours. An ulcer destroying at least 50% of stromal thickness needs assessment for surgery by a veterinary ophthalmologist.

A conjunctival graft strengthens the weakened cornea. The graft is sutured over the ulcer under general anaesthesia. Surgical follow-up checks may be at one and three weeks, for example. Suturing the third eyelid over the ulcer makes surface monitoring and topical treatment more difficult.

Prevention

A protective collar that prevents eye rubbing reduces further self-inflicted damage. A collar is also needed with a bandage contact lens. Correcting a rubbing eyelid or eyelash removes a source of ongoing mechanical injury. Treating dry eye is part of addressing factors that prevent healing.

Keep shampoo and other irritating chemicals out of the eyes. Avoiding injuries cannot prevent every indolent ulcer, because they can also arise spontaneously.

Incomplete eyelid closure is among the factors that complicate ulcer management; correcting it supports healing.

Important for dog owners

Healing is confirmed with repeat fluorescein staining. Agree with the vet when to stop treatment. The cornea normally has no blood vessels. Red vessels growing towards an ulcer are the body's way of supporting healing.

Do not use old corticosteroid eye drops on an open corneal ulcer: they can slow or stop healing. The topical anaesthetic drops used during examination are unsuitable for repeated pain relief at home because they can damage the cornea. A pupil-dilating medicine used for pain relief can make the eye sensitive to light.

Eye medication can travel through the tear drainage system to the throat, where the dog tastes it. A bitter taste can cause drooling. However, a clear increase in eye pain after medication requires immediate contact with the vet.

Frequently asked questions

Will a corneal ulcer heal by itself?

An uncomplicated superficial ulcer usually heals in three to five days with appropriate treatment. However, an ulcer can worsen rapidly and threaten sight. A squinting or painful eye therefore needs examination. A deep ulcer may require surgery.

Why is the ulcer not healing with antibiotic drops?

In an indolent ulcer, the problem is poor attachment of surface cells to the tissue beneath. An antibiotic alone does not usually correct this. The ulcer may need removal of loose epithelium and treatment of the surface layer. Dry eye or ongoing mechanical irritation can also prevent healing.

Does my dog need a collar if there is a contact lens in the eye?

Yes: rubbing with a paw or against a surface can damage the regrowing epithelium. A bandage contact lens protects exposed nerve endings and improves comfort. After SCCED treatment, the collar stays on until follow-up. This is usually 10–14 days after the procedure.

Can a corneal ulcer make a dog blind?

Yes: a progressive ulcer can cause loss of sight. A deep lesion can also perforate the eye. A severe ulcer sometimes needs immediate surgical support. Even after healing, corneal scarring may reduce transparency.

Can I use previously prescribed corticosteroid eye drops?

Corticosteroid drops can be dangerous for an open corneal ulcer because they slow or stop healing. Ulcer closure is confirmed by a staining test before such treatment is started. They may sometimes be prescribed for a fully healed eye to reduce blood vessels that are causing problems.