Cherry eye in dogs: symptoms, diagnosis and treatment

Overview

As well as upper and lower eyelids, dogs have a third eyelid, or nictitating membrane. This is a thin membrane at the inner corner of the eye, inside the lower lid. The gland normally lies at the base of the third eyelid and is not visible from outside. The smooth lump of tissue seen with prolapse is this gland.

Cherry eye is the most common disease of the third eyelid. Among dogs receiving primary veterinary care in Britain, 0.20% were diagnosed with it during 2016. One or both eyes can be affected. The two eyes do not necessarily develop signs at the same time.

The third eyelid and the main eyelids spread the tear film over the eye's surface. The tear film keeps the eye moist and supports surface health.

Causes

Weakness of the structures holding the gland in place is considered a main cause. Connective tissue at the gland's base then fails to support it adequately. Inherited susceptibility is suspected because the condition occurs in particular breeds and family lines. However, the precise initiating mechanism is not known in every dog.

An exposed gland comes into contact with air and becomes irritated. It may swell and become redder. Its small tear ducts can become kinked, making drainage difficult. Inflammation and enlargement can stretch the gland's supporting attachments further.

The gland can also become vulnerable to infection when it remains outside its normal protected position. A damaged connective tissue attachment does not return to normal simply by reducing gland swelling.

The tear film has mucous, watery and oily layers. Reduced tear gland function particularly decreases the watery component.

Risk factors

Cherry eye most often develops in young dogs, usually before 2 years of age. Signs are described particularly at around 3 months–1 year of age. Older dogs can also be affected.

Susceptible breeds include Beagles, English Bulldogs, French Bulldogs, American Cocker Spaniels and Boston Terriers. The condition is also seen in Lhasa Apsos, Shih Tzus and Poodles. In short-nosed breeds, the structure of the eye socket and eyelids can predispose to gland prolapse.

In the British dog population studied in 2016, the annual proportion was 4.75% in English Bulldogs compared with 0.15% in crossbreeds. These figures describe diagnoses during that year, rather than a dog's lifetime risk.

The median age at first diagnosis in the British dogs was 0.63 years. Young age at onset and differences between breeds support the possibility of inherited susceptibility.

Typical symptoms

The most typical finding is a smooth, rounded, pink or red tissue mass protruding from the inner corner of the eye. At first, the gland may be visible only intermittently. It may slip back and reappear later.

• A red swelling is visible at the inner corner of the eye.
• The conjunctiva becomes red and inflamed.
• The eye produces discharge.
• Your dog rubs or scratches the eye because of irritation.
• The gland gradually looks more swollen.

Pain may initially be mild even when the gland is clearly visible. Thick yellow-green discharge, squinting and a dry-looking surface can be associated with established dry eye.

Rubbing can injure the gland's surface and make it bleed. A gland exposed for a long time is more prone to irritation and inflammation.

Complications and consequences

The third eyelid gland produces a substantial proportion of the watery component of tears, estimated at about 33–66%. Its contribution is also estimated at about 40–60%. Removing the gland increases the risk of dry eye later. Simply getting rid of the red lump by removing the gland can therefore harm the eye's moisture balance.

In dry eye, too little of the watery tear component is produced and the eye's surface becomes inflamed. This can lead to a painful corneal ulcer. Long-term consequences can include scarring, blood vessel growth in the cornea and permanent loss of vision. Dry eye often requires lifelong treatment.

The outlook after surgery is usually good. The estimated success rate for repair by a veterinary ophthalmologist is about 92%. Recurrence is below 8%. Recurrence is possible particularly when the gland has been exposed for a long time or is severely inflamed. An uncorrected cartilage abnormality in the third eyelid can also increase recurrence.

Uncommon complications of repair include a suture reaction, corneal ulceration or infection, and ongoing inflammation. Third eyelid movement may be reduced after the procedure. However, function and appearance usually remain good.

Long-standing dry eye can also cause dark pigment to develop in the cornea.

Diagnosis at the vet

The vet examines the protruding tissue and the surface of both eyes. A typical prolapsed gland is often recognised by appearance. The third eyelid is also checked for abnormally shaped cartilage. In rare, atypical changes, a tumour is considered as a possibility.

Everted third eyelid cartilage can look like a similar red swelling. In this condition, the T-shaped supporting cartilage grows and bends abnormally. Cartilage eversion is more common in giant breeds such as Great Danes. Gland prolapse and cartilage eversion can also occur together. Sometimes they can only be distinguished during examination under general anaesthesia.

Tear production is measured with a Schirmer tear test when needed. This assesses watery tear production over 1 minute. If corneal damage is suspected, fluorescein stain is applied to the eye's surface. The dye adheres to the damaged area and makes an ulcer visible.

In a Schirmer test, a graduated paper strip is placed under the eyelid, where tears soak into it. Wetting of more than 15 mm in a minute is considered normal. A lower result may indicate dry eye.

Treatment

The vet prescribes treatment and assesses whether help from a vet with expertise in eye disease is needed. The usual approach is surgical replacement of the gland within the third eyelid. The aim is to preserve a functioning tear gland.

For a small change causing few signs, lubricating and anti-inflammatory eye drops chosen by the vet may be used initially. A recent, small prolapse can sometimes be replaced at the practice under local anaesthesia. However, a manually replaced gland later prolapses again in many dogs.

In a pocket procedure, a supporting pocket is created beneath the third eyelid's conjunctiva. Scar tissue forming inside the pocket holds the gland in position after the suture dissolves. Another technique anchors the gland to firmer tissue around the eye socket. The surgeon may also combine techniques.

If the third eyelid cartilage is bent, the abnormal section may be reshaped or removed at the same time. Removing the gland is reserved for rare situations in which tissue is not viable, for example because of a tumour or severe injury. Preserving the gland is otherwise the basic treatment principle.

Topical medicines may be needed after surgery to control inflammation, pain and infection. A protective collar prevents rubbing and scratching. The first recheck may be after 10–14 days, with another about 1 month later.

Abnormally long eyelids can leave the gland inadequately supported. If this structure is identified, correction of eyelid length may also be needed to prevent recurrence. Replacing the gland alone then does not correct the whole structural problem.

If dry eye has already developed, treatment may include both tear substitutes and medicines that increase the dog's own tear production. Lubricants are available as drops, gels and ointments. A medicine stimulating tear gland function takes several weeks to develop its full effect. Some dogs show signs of improvement in dry eye only after 12 weeks.

Preserving the gland during repair reduces the dry eye risk associated with losing it. Preventing rubbing after surgery is part of recovery care. Keep the collar on until the vet treating your dog allows it to be removed.

In dry eye treatment, ciclosporin or tacrolimus can increase tear production and reduce inflammation. A secondary bacterial infection may require a topical antibiotic. Any eye surface disease that has already developed is treated alongside gland repair.

A repair anchored around the eye socket may leave a separate skin suture beneath the eye. This is removed at a follow-up appointment after surgery.

Lubricating the eye's surface and supporting the dog's own gland function are different treatment aims. Preserved gland tissue also supports later medical treatment, as medicines increasing tear secretion generally require the third eyelid gland to be present.

Prevention

Cherry eye cannot reliably be prevented in an individual dog, as there is no home correction for congenital weakness of the supporting tissue. Early treatment gives the gland the best chance of functioning normally. Some breed-club guidance permits breeding from an affected dog with a healthy mate where there is a justified reason. Because of the risk of inheritance, excluding affected dogs from breeding altogether is also recommended.

Tear production monitoring continues even after successful repair. Tear levels in both eyes may be checked at least twice a year. Prolapse lasting a long time before surgery particularly increases the risk of dry eye later.

Important for dog owners

Record which eye was affected first and when the change first appeared. Take a photograph while your dog is calm so the vet can see a swelling that sometimes disappears. Note rubbing, keeping the eye closed and changes in discharge separately. Bring previous eye examination results and details of eye products used.

Ask for written instructions on collar use and what the eye may look like immediately after surgery. Confirm whom to contact if the gland becomes visible again. Also arrange later monitoring of tear production in both eyes. If you cannot give the drops, tell the veterinary team so daily treatment can be made practical.

Frequently asked questions

Is cherry eye a tumour?

Usually it is a tear gland that has moved out of position. However, other changes can occur in the same place, including, rarely, a tumour. A new swelling therefore needs examination even if it resembles cherry eye in a dog you know.

Can the gland simply be removed?

In ordinary cherry eye, the aim is to preserve the gland because removal predisposes to dry eye. Removal is rarely needed, for example because of non-viable tissue or a tumour. The vet examining the eye assesses tissue viability and any possible tumour before deciding on removal.

Can cherry eye disappear on its own?

The swelling may sometimes slip back and reappear later. A small change may initially be treated with drops selected by the vet. A persistently exposed gland usually needs surgical replacement to return it to the protection of the third eyelid.

Can cherry eye develop in the other eye too?

Yes. The eyes may be affected at different times, so an initially one-sided change does not mean the other eye is permanently protected. A new swelling or irritation in the other eye also needs examination, and tear production in both eyes is monitored afterwards.

Can surgery fail?

The gland can prolapse again after repair, although the outlook is usually good. Another procedure may be needed to return the same gland to its position again. Long-standing inflammation and an uncorrected cartilage abnormality increase the chance of recurrence.