At a glance
Squinting can be a normal behaviour when the cat is relaxed and trusting but it can also be a sign of an underlying disorder.
Squinting occurs when the cat looks at you with his eyes half closed. In healthy cats, squinting is a normal part of communication and he is telling you he is relaxed and trusts you, when light suddenly increases before the pupils have time to constrict. Sometimes however, squinting is a symptom of an underlying problem with the eyes. This article focuses on the medical causes of squinting.
The eyes are vulnerable to a number of disorders, many of which present as squinting among other symptoms.
Blepharitis is an inflammation of the eyelid margins and surrounding skin and in some cases, the Meibomian glands, which are tiny glands on the eyelid margin which secrete an oily substance to keep tears within the eye. There are a number of causes which include:
- Parasites: Sarcoptic or demodectic mange
- Bacterial infection: Staphylococcus
- Viral infections: Feline herpes virus
- Eyelid abnormalities (due to chronic moistness or trauma): Distichia (abnormally located eyelashes), inward turning eyelashes, entropion (eyelid which rolls inward), lagophthalmos (inability to close the eyelid completely)
- Allergic: Food, inhaled, contact, insect or drugs
- Tumours: Squamous cell carcinoma, mast cell tumour
- Immune mediated: Pemphigus
- Fungal infection: Histoplasmosis or ringworm
- Trauma: Lacerations or burns (chemical, thermal)
- Irritants: Medications applied to the eyes, cigarette smoke, pollen and chemicals
- Idiopathic: Unknown cause
- Eye discharge which may contain pus, mucus or watery discharge
- Irritated, watery eyes
- Eyelid redness (hyperemia)
- Inflammation of the eye margins
- Thickening of the eyelids
- Hair loss
- Pawing the eyes due to irritation
- Sensitivity to light (photophobia)
- Inflammation of the cornea
- Squinting or spasmodic blinking (bleptospasm)
The goal of treatment is to address the underlying cause. In addition, managing underlying symptoms can include:
- Use a warm compress for 5-10 minutes, 3-4 times a day to loosen crusts from the eyes and to help unclog the glands. Clip the hair around the eyes.
- It may be necessary to use an Elizabethan collar on the cat to prevent further damage due to self trauma.
Also known as hard eye, glaucoma is an increase in the intraocular pressure (IOP), leading to damage to the optic nerve, which connects the eye to the brain. Any damage can cause partial or full blindness.
- Trauma, which can cause bleeding in the eye
- Lens luxation (displacement of the lens)
- Cataract surgery
- Advanced cataracts
- Eye tumours
- One eye may look larger than the other as the pressure increases
- Dilated pupil
- Cloudiness of the cornea
- Vision loss
- Osmotic agents: These systemic medications can reduce IOP rapidly and works by increasing blood plasma osmality, once plasma osmality is greater than that of the intraocular fluid, water moves from the eye to the plasma reducing IOP. Mannitol, glycerin and isosorbide are the most common osmotic agents.
- Carbonic anhydrase inhibitors: CAI’s reduce the formation of bicarbonate ions, which is necessary for aqueous humour production. Medications include topical and oral medications. Topical: dorzolamide and brinzolamide or oral: methazolamide and acetazolamide.
- Prostaglandin analogues: These drugs increase intraocular fluid from the eye. Medications include prostaglandin analogs such as latanoprost, travaprost, unoprostone and bimatoprost.
- Beta-blockers: These medications reduce aqueous humour production although the exact mode is not understood. The most used medication is Timolol, but other options include evobunolol, betaxolol, metipranolol and carteolol.
- Steroids: To reduce inflammation.
- Cryosurgery: To freeze a portion of the ciliary body which reduces the production of aqueous humour.
Uveitis is an inflammation of the uvea, the pigmented layer that lies between the inner retina and the outer fibrous layer composed of the sclera and cornea. It is one of the most common eye disorders in cats.
- High blood pressure
- Eye tumours, the most common being diffuse iris melanoma and lymphoma.
- Bartonella henslae (cat scratch disease)
- Feline infectious peritonitis (FIP)
- Feline immunodeficiency virus (FIV)
- Feline leukemia virus (FeLV)
- Blunt or penetrating injuries
- Lens-induced anterior uveitis is caused when the lens capsule breaks open leaking fluid into surrounding tissues, which causes an inflammatory response. Other causes include hyper-mature cataracts and lens luxation.
- Idiopathic (no known cause)
- Colour change to the eye(s), which may be cloudy or red
- The pupil may be small and unevenly shaped
- Protrusion of the third eyelid
- Redness of the third eyelid
- Sensitivity to light (photophobia)
- Watery discharge
- Inflammation can cause the eye to become softer (hypotonic)
Treatment of uveitis is aimed at addressing the underlying cause, if it is known, reducing inflammation, relieving discomfort and preventing further damage to the eyes. This may include:
- Anti-inflammatory therapy. Corticosteroids may also be administered systemically, subconjunctivally (under the conjunctiva) and topically.
- Topical atropine ointment if necessary to keep the pupils dilated which relieves pain and stops the inflamed iris sticking to the pupil, which causes further damage to the eye.
- Antibiotics to treat bacterial and protozoal infections.
- Diabetes should be brought under control, this usually involves a change in diet and/or insulin injections.
- Viral infections are usually managed with a combination of anti-viral medications (where available) and supportive care while your cat fights the disease.
- Eye removal (enucleation) to treat eye tumours.
- Steroids to treat immune-mediated disorders.
Also known as pinkeye, conjunctivitis is a common disease in cats characterised by inflammation and pinkness of the conjunctiva, the pink membrane which covers the front of the eyeball and the inside of the eyelids. It can affect one eye (unilateral) or both eyes (bilateral) and covers a broad range of possible conditions. Conjunctival inflammation can be acute or chronic, infectious or non-infectious.
- Feline herpesvirus (FHV-1) is an acute upper respiratory tract infection, kittens and cats in overcrowded environments such as shelters are most commonly affected.
- Calicivirus is another common upper respiratory infection which is most often seen in kittens, overcrowded environments or immunocompromised cats. FHV-1 and Calicivirus are responsible for 80-90% of upper respiratory infections in cats.
- Feline Chlamydophila is a bacterial infection characterised by mind rhinitis, fever, localised lymph node swelling and ocular discharge.
- Mycoplasma is an unusual class of bacteria which lack cell walls.
- Bartonella is the bacteria responsible for cat scratch disease in cats. Infected cats generally have mild and self-limiting symptoms including fever, swollen lymph nodes, uveitis, and conjunctivitis.
Most bacterial infections occur secondary to viral infections when irritation or damage to the sensitive tissues of the eyes expose them to opportunistic bacterial infections, common pathogens include Streptococci and Staphylococci.
- Allergies (plants, pollens etc).
- Blepharitis is an inflammation of the eyelid, which causes swelling and discomfort. Swelling can lead to irritation of the underlying conjunctiva.
- Foreign object (grass seed, hair, sand, eyelash).
- Irritants (eg; smoke, fumes, dust).
- Injury (scratch).
- Entropion is a condition in which the eyelids fold inwards, this causes the eyelashes to rub against the eye, which causes irritation. Persians and Exotics are particularly at risk of this.
- Eye tumours.
- Keratoconjunctivitis sicca (KCS/dry eye) – This is an inflammation of both the cornea and the conjunctiva and sicca means dry. This is caused by a lack of tears reaching the surface of the eyes which is caused by trauma, inflammation of the conjunctival glands and ducts, scarring etc. 
- Keratitis is an inflammation of the cornea, there are a number of causes including infectious and non-infectious. It is possible for inflammation to progress to the conjunctiva.
- Ocular (eye) discharge. This will vary depending on the cause of conjunctivitis, it may either be clear and watery or thick, containing mucus or pus. Thick and purulent discharge is more often due to bacterial infection (primary or secondary), watery discharge is more likely to be due to allergy or irritants
- Eye discharge along with a meaty like appearance to the eye
- The conjunctiva becomes red and swollen
- Pawing and rubbing at the eye
- Third eye protrusion
- Ulceration of the eye may also occur in cats infected with FHV-1
Treatment depends on the cause of conjunctivitis. Mild cases of conjunctivitis may only require flushing of the eye with a saline solution. Determining the causative agent where possible.
- Purulent conjunctivitis requires eye irrigations and warm saline soaks to loosen crusted eyelids.
- Antibiotic eye ointment (usually topical tetracyclines) applied several times a day to treat bacterial infections.
- Systemic antibiotics if your cat has Chlamydophila, recent research has revealed the pathogen may hide away in non-ocular sites.
- Antiviral eye medications.
- Antibiotics to treat secondary bacterial infections which can develop in cats with viral conjunctivitis.
- L-Lysine to suppress viral replication of the herpes virus.
- Other treatments for cats with chronic FHV-1 conjunctivitis may include topical or systemic interferon and systemic anti-virals such as aciclovir.
- Removal of the allergen where possible and anti-inflammatories to treat allergies.
- If a foreign object is the cause, removal should solve the problem. This usually involves irrigating the eye with a saline solution to dislodge the object.
- Artificial tears to keep eyes moist for cats with dry eye.
- Cyclosporine is an immune modulating medication that can help suppress immune system inflammation of the tear glands.
- Entropion may require corrective surgery.
Foreign material in the eye
Due to the sensitivity of the outer portion of the eye, debris can cause extreme discomfort. Dust, eyelashes, grit and pollen are all common culprits.
- Pawing at the eye
- Watery eye
- Sensitivity to bright lights
Tear production may be enough to flush the material out of the day, if symptoms continue for more than a few eyes, seek veterinary attention as the material can scratch the cornea, resulting in ulceration. A veterinarian will be able to flush the material out of the eye.
Medically known as keratoconjunctivitis sicca (KCS), dry eye syndrome (DES) is a condition characterised by insufficient watery tears reaching the surface of the eye which leads to dryness of the cornea and the conjunctiva. As a result, they become irritated and inflamed due to the lack of lubrication and moisture.
- Immune-mediated inflammation and/or destruction of the tear glands, the cause of this is not known
- Inflammation of the eyelid (blepharitis) which can cause inflammation and disrupt normal tear production
- Certain drugs such as general anesthetic, sulfa antibiotics, and atropine
- Damage to the facial nerve which activates the tear glands, most commonly due to a middle ear infection
- Removal of the nictitating membrane (third eye) to treat cherry eye
- Congenital dry eye can occur in Burmese cats due to prolapsed glands
- Excessive blinking
- Thick, stringy mucoid discharge particularly around the rim of the eyes
- Painful red eyes
- Reluctance to open the eyes
- Swollen eyelids
- Dry, dull and opaque appearance to the cornea
- Sensitivity to light (photophobia)
- Cyclosporine is an immune modulating medication which can suppress immune system inflammation of the tear glands. Administer twice a day. Long-term use is safe, and there are no residual side effects, however stinging in the eye may occur. It can take several weeks for the effects of cyclosporine to take effect.
- Artificial tears three times a day to keep the eye moist and lubricated. These are the same products people use and are available over the counter from all pharmacies.
- Antibiotics to treat secondary bacterial infections.
- Topical corticosteroids may be necessary to treat eye inflammation.
- Cats who don’t respond to treatment may require parotid (salivary) duct transposition surgery. This involves moving the parotid duct which is located in on either side of the cheeks up towards the eyes so they can act as additional tear ducts. Saliva and tears are very similar in composition. While this surgery is usually successful, eye drops may still be required.
The pupil is the black slit/circular shape you see in the middle of the cat’s iris (the coloured part of the eye). The role of the pupil is to control the amount of light entering the eye. It does this by dilating (becoming large) and constricting (becoming small/slit-like). Some medical conditions can cause a dilation of the pupils which can result in light-sensitivity.
- Brain trauma
- Key-Gaskell sydrome
- Thiamine deficiency
- Retinal detachment
- Tumours (brain or insulinomas)
- Feline dysautonomia
- Hypocalcemia (low blood calcium)
- Anticholinergic drugs and plants
Symptoms can vary depending on the underlying cause, but can include:
- Enlarged pupils which do not respond appropriately to light (in the normal eye, the pupils will decrease in size when exposed to light
- Sensitivity to light
Treatment depends on the underlying cause. In some cases, your veterinarian will recommend your cat be kept in a darkened room until the cause has been treated.
A corneal ulcer is an open sore of the cornea, which is the transparent dome-shaped layer covering the front of the eye including the iris, pupil, and anterior chamber.
The outer layer of the cornea can be damaged due to scratches, particularly in younger cats, this is known as a corneal abrasion. Cells quickly repair this damage.
Erosion of the cornea, typically involving more than one layer is known as a corneal ulcer or ulcerative keratitis and can occur due to the following:
- Injury or trauma (such as rubbing an itchy eye)
- Infection (such as fungal infection, herpes or calicivirus)
- Damage due to structural abnormalities such as entropion, dry eye (lack of tear production) and foreign body.
- Pain, due to the rich supply of nerves, the deeper the injury, the greater the pain
- Ocular discharge
- Sensitivity to light
- Excessive tear production (epiphora)
- Eyelid spasms (blepharospasm)
- Cloudiness of the cornea
Treatment is aimed at addressing the underlying cause and helping the cornea heal while controlling inflammation, pain and preventing secondary infection. This may include drops to stimulate the production of tears, supportive care and/or anti-virals, anti-fungal medications, surgery to correct eyelid abnormalities.
- Atropine is a medication which causes the pupil to dilate and helps relieve pain as spasms of the ciliary muscle (which controls the dilation and constriction of the pupil) cause pain in the already damaged cornea. Unfortunately, as the pupil is dilated, the eye becomes more sensitive to light, therefore your cat should be provided with a darkened room he can use if necessary.
- Antibiotics to treat or prevent bacterial infection.
- More serious corneal ulcers will necessitate the eye be protected while the ulcer heals. This usually involves suturing the eyelid shut for several days which is medically known as a tarsorrhaphy.
- If your cat is continuing to paw at the eye, an Elizabethan collar may be used.