Abscess behind a dog's eye – symptoms and treatment

Overview

Inflammation lies behind the eyeball

The retrobulbar space is the part of the eye socket behind the eyeball. Eye muscles, nerves and blood vessels pass through it. The tear gland and zygomatic salivary gland are also nearby. A dog's eye socket is not completely surrounded by bone. Its lower portion also includes muscle and salivary gland tissue.

An abscess is a collection of pus within tissue. Orbital cellulitis means inflammation of the tissues in the area. Both can cause a bulging eye and pain on opening the mouth. They cannot be reliably distinguished by appearance alone.

Outward displacement of the eye is called exophthalmos. This differs from enlargement of the eyeball itself, for example with long-standing raised intraocular pressure. Depending on its location, a lesion pushing the eye outwards may displace it straight forwards or to one side.

Causes

Infection can start in the mouth or an injury

The mouth lies below the eye socket. The roots of the upper back teeth are close to the orbital floor. A tooth root infection can therefore spread behind the eye. A grass awn migrating through tissues can also cause infection behind the eye. A foreign body can carry bacteria into deep tissues.

A bite injury can also cause a retrobulbar abscess. Infection may spread from the nasal cavity or sinuses. Sometimes inflammation of the zygomatic salivary gland is responsible.

The starting point is not always found

Both oxygen-requiring bacteria and bacteria living without oxygen can be isolated from infections behind the eye. This affects which antibiotic will work. In a US abscess and cellulitis study, tooth root abscessation was the cause in 23.7% of dogs. In half, or 50%, the cause remained unknown.

Risk factors

A foreign body, bite or untreated dental disease increases the possibility of this particular infection. A fractured or damaged tooth can become infected and form an abscess. Periodontal disease can also underlie a dental abscess.

In a 2018 study, dogs with primary retrobulbar infectious or inflammatory disease ranged from 1–13 years old. The median age was 6 years. The mean age was 7.0 years. Both male and female dogs were affected.

Different breeds and crossbreeds were represented. The size of breed-specific disease risks is unknown.

Typical symptoms

Signs can develop quickly. Nasal discharge, sneezing or nosebleeds may also suggest concurrent nasal disease. At home, you may notice:

• One eye bulges or appears displaced sideways.
• The third eyelid rises from the inner corner and becomes more visible than usual.
• The area around the eye is swollen and tender.
• Your dog is reluctant to open their mouth or chewing hurts.
• Eye discharge, sometimes containing pus.
• Fever, lethargy or loss of appetite.
• Part of the eye surface remains exposed during blinking.

Pain on mouth opening occurs because lower jaw movement presses on inflamed orbital tissues. This can initially make an eye condition look like toothache or a jaw problem. Early orbital cellulitis can resemble ordinary conjunctivitis.

Complications and consequences

The eye surface and vision are at risk

Incomplete blinking predisposes the cornea to drying and ulceration. Sampling in the area also carries a risk of haematoma and optic nerve damage. Severe tissue swelling can compress orbital veins and raise intraocular pressure. Infection behind the eye can also cause vision loss.

In the US abscess and cellulitis study, 15.8% of dogs already had impaired vision at the initial examination.

Prolonged difficulty eating may require nutritional support.

Inflammation can settle with treatment

The prognosis for an appropriately treated retrobulbar abscess is generally good. In the 2018 study, 19 dogs had primary retrobulbar infectious or inflammatory disease. Of these, 12 responded to treatment or became clinically free of signs. The later treatment outcome remained unknown in 7 dogs.

Diagnosis at the vet

The eye, mouth and teeth are examined together

Your vet assesses eye position, surrounding swelling and findings relating to vision. The mouth is examined for swelling and possible fistulous tracts, among other changes. Inflamed, swollen mucosa may be present behind the last upper molar. Opening the mouth can be very painful. Examination therefore takes pain relief and safety into account.

A blood test may show an increased white blood cell count.

Dental X-rays are needed if an upper back tooth root infection is suspected. Sudden onset more often fits inflammation. An advanced tumour can nevertheless also be painful. A tumour, salivary fluid collection or another space-occupying lesion can also push the eye outwards.

Your vet may assess whether the eye moves gently backwards into the socket. A space-occupying lesion can reduce this movement. The 2018 CT study included 66 dogs with retrobulbar disease in total. In 22 dogs, reduced backward movement was not detected or the finding was not recorded. This represented 33.3%. This examination finding is therefore not always clearly abnormal despite disease deep in the socket.

Myositis, or muscle inflammation, of the eye-moving or chewing muscles can also cause signs of orbital disease. Orbital bleeding is another possible cause and can be associated with injury or a clotting disorder.

Imaging locates the lesion

Orbital ultrasound can reveal tissue changes or help guide sampling. Computed tomography, or CT, shows the extent of changes in the socket and nearby areas. MRI can also be used. Ultrasound may be particularly useful for finding a foreign body such as plant material. Images can help locate a foreign body and plan an approach for the procedure.

CT findings of tumours and inflammation can partly resemble one another. Bone destruction or new bone formation is, however, more often associated with a tumour. A definitive diagnosis may require cell, tissue or microbial samples.

Imaging may also show enlargement of the mandibular lymph nodes and zygomatic salivary gland. Tissue displacement without a clearly distinct mass is consistent with inflammation.

Culture helps select treatment

An ultrasound-guided fine-needle sample can be submitted for bacterial culture and susceptibility testing. Susceptibility testing establishes which antibiotics affect the bacterium found. In the US abscess and cellulitis study, 83.3% of cultures yielded bacterial growth. Both aerobic and anaerobic bacteria are considered. A negative culture is also possible in a sterile abscess or tissue inflammation. The area's complex anatomy can make sampling the affected tissue difficult. If cytology and tissue sample results differ, both may be needed to clarify the diagnosis.

Treatment

Treating infection and pain

Your vet prescribes antibiotics according to the infection and any culture results. Treatment must cover anaerobic bacteria, which grow without oxygen, where necessary. Pain is managed with relief suitable for your dog. Nutritional support is provided if your dog is not eating.

Clear improvement in signs is expected within 2–3 days of suitable antibiotic treatment. This describes assessment of the response, rather than an instruction to stop medicine once signs improve. The overall treatment and follow-up depend on the location and cause of infection.

Addressing the abscess cavity and its cause

A pus collection can be drained through the mouth under general anaesthesia. Imaging helps confirm the target for drainage. Inflamed tissue alone is not opened blindly. A blind procedure can damage the optic nerve and other orbital structures.

Some early orbital infections settle with medication without drainage. A foreign body is removed if it sustains the abscess. A dental infection may require extraction of affected teeth. Recurrence can lead to repeat imaging or surgical exploration.

In the US abscess and cellulitis study, 78.9% of dogs were managed medically. Surgery was used in 18.4%.

Protecting the eye surface

An eye that does not close fully can be protected with topical lubrication. In a severe case, the eyelids may be temporarily partially stitched together. Corticosteroid eye drops may be contraindicated because the cornea is exposed. Do not treat an untreated infection with oral corticosteroids on your own initiative either.

If an eye is blind and painful and infection does not settle, removal of the eye or orbital tissues may be considered. Eye-preserving abscess debridement is another possible surgical option.

Prevention

Not every orbital infection can be prevented because the starting point remains unknown in some cases. Preventing dental disease and treating damaged teeth reduce the possibility of dental infection.

A fractured tooth should be examined early so that any treatment is easier to carry out. Regular toothbrushing also helps identify fractures and colour changes. Chewing very hard objects can fracture a tooth. A bite or a foreign body remaining in the mouth needs examination because either can be associated with an abscess behind the eye. A protective collar prevents eye rubbing where needed.

Important for dog owners

Record when eye position or mouth opening changed and whether signs have worsened rapidly. Mention any bite, foreign body entering the mouth and previous dental observations. Take a comparison photograph of both eyes without touching the eyeball. Do not press on a bulging eye or try to open the abscess area at home. Opening the mouth can be very painful.

During treatment, monitor eating, drinking, eye closure and your dog's general condition. Follow prescribed medication and agreed follow-up times. Suitable treatment should produce clear improvement within 2–3 days. Deteriorating vision or increasing bulging requires prompt reassessment.

Report recurrent signs to the treating vet as well. A foreign body left in place can cause the abscess to return. The eye surface needs protection for as long as blinking remains incomplete.

Frequently asked questions

Can an abscess behind the eye look like an ordinary eye infection?

Early orbital cellulitis can resemble conjunctivitis. Pain on mouth opening and outward displacement of the eye fit a deeper problem. Investigating the cause may require orbital imaging and sampling. Redness of the eye surface alone therefore does not establish the appropriate treatment.

Why does opening the mouth hurt with an abscess behind the eye?

The mouth and eye socket are anatomically close. When the mouth opens, lower jaw movement presses on orbital tissues. This causes pain in inflamed tissue. The closeness of upper back tooth roots to the orbital floor can also explain a link between a tooth and eye signs.

Does every orbital infection need surgery?

Some orbital infections may settle with medication. A confirmed pus collection may nevertheless need drainage. If a foreign body is responsible, it must be removed to prevent recurrence. Blindly opening inflamed tissue through the mouth risks damage to the optic nerve and other orbital structures.

How quickly should treatment improve the signs?

Clear improvement is expected within 2–3 days of suitable antibiotic treatment. This is assessment of response, rather than the length of the antibiotic course. Recurrent infection may require surgical exploration. An underlying foreign body must also be removed so that the abscess does not return.

Will my dog's eye need to be removed?

An abscess behind the eye can also be treated while preserving the eye. If the eye is blind or treatment does not help, however, removal of the eye or orbital tissues may be needed for pain relief. The procedure is determined by your dog's vision, pain and extent of inflammation.