It may not be easy to tell if your pet is experiencing eye pain. For most small mammals, hiding illness and pain is the way they survive. Due to their instincts to hide pain and illness, you may only notice subtle behavioral changes, such as sleeping more, hiding, decreased appetite, reduced playfulness, and an aggressive disposition. The connection of these vague expressions to eye disease is often only made after the pet has resumed his "normal" pattern of behavior. Other signs may include: Squinting of the eyelids. This is a hallmark symptom of pain that brings immediate attention to the eye. Squinting can be observed in eyes with irritation of the eye surface or when irritation originates from within the eye.
Pupil and iris changes. The cornea and conjunctiva have a rich concentration of pain fibers (nerves), with the highest proportion located near their surfaces. This correlates to large, superficial ulcers of the cornea being much more painful than smaller, deeper ulcers. The severe pain from a corneal ulcer or scratch can also stimulate reflex pain inside of the eye, as the iris also contains a high number of pain fibers. When this occurs, the pupil becomes constricted, the iris becomes swollen and the conjunctiva reddened. A specific ophthalmic medication, called atropine, is used to treat this type of pain.
Inflammation of the iris. Pets that develop anterior uveitis (inflammation of the iris) will typically show symptoms of eye pain. There are numerous causes of uveitis. Systemic infectious diseases can manifest or "settle" in the eyes of pets, but cancerous and immune system diseases can also affect the iris resulting in anterior uveitis. The cause of anterior uveitis in many animals is not determined and the disease is called idiopathic. Diagnostic tests are necessary in all cases to identify the underlying cause of the uveitis when possible and to initiate appropriate treatment.
In contrast to the cornea, conjunctiva and iris, the retina and optic nerve have no pain sensation. Therefore, diseases such as retinal degeneration, retinitis (inflammation of the retina) and optic neuritis (inflammation of the optic nerve) are often referred to as "silent" diseases.
Photophobia. Eye pain can be aggravated by bright light. This symptom is commonly associated with severe eye disease. Pets that are treated with atropine have dilated pupils as a side effect of the medication. Animals treated with atropine continue to be mildly photophobic until the medication is discontinued.
What to Watch For
Squinting is the most obvious symptom of eye pain. Other symptoms may include:
Mucoid or pus-like ocular discharge
Bloodshot or reddened conjunctiva
Cloudiness or bluish haze or film covering the eye
Dilated, constricted or unequal pupil sizes
Excessive pawing or rubbing of the eyes
Swelling of the eyelids or eyeball
Protrusion of the third eyelid
Reduced vision or blindness
Lethargy (lack of energy)
Veterinary care should include diagnostic tests to determine what is causing the symptoms of eye pain and to direct subsequent treatment. Some tests may not be possible on all small mammals due to size of the pet and cost concerns. There are several potential diagnostic tests which include:
Complete medical history and physical examination
Complete ophthalmic examination
Schirmer tear test
Fluorescein staining of the cornea
Forcep examination of the eyelids under topical anesthesia
Cytology (complete cell analysis) and culture of cells collected from corneal wounds or ulcers
Complete blood count
Skull radiographs (x-rays)
Treatment depends on the cause of the eye pain and squinting. There is no general treatment for these symptoms. Treatment may involve medical treatment, surgical intervention, or both to stabilize the painful ophthalmic condition.
Recommendations for home care will depend upon the underlying cause of the problem. Seeking immediate veterinary medical attention is critical, as many causes of eye pain and squinting are vision threatening and most require specific medical and/or surgical treatment.
Gently clean away excessive eye discharge with a warm moist cloth to prevent crusting and caking of the hair around the eyes. Cease all attempts if the pet becomes aggressive or if pain seems intense.
If vision appears to be impaired, minimize stress and risk of injury by confining the pet to a safe area until the cause of the problem is determined.
Keep the pet in a dimly lighted area or room as most pets are photophobic and are more uncomfortable in bright lighting conditions.