Why Is My Cat Keeping One Eye Closed? 7 Common Causes and Solutions

As a doting cat parent, you know your furry companion better than anyone. So when you notice something amiss like Fluffy keeping her left eye shut for hours on end, alarm bells go off in your head. An eye that remains half-closed despite your efforts to gently pry it open likely signals an underlying issue that warrants attention. But what could be causing this?

In this comprehensive article, we will embark on an investigative journey to unravel the mystery behind your cat’s squinting eye. Just like an episode of detective show Blue Bloods, we will gather clues, analyze evidence, and methodically rule out suspects until we crack the case. The culprits we seek are the diseases, injuries and annoyances that drive our feline friends to squeeze their eyes tight and refuse to open them.

Arm yourself with patience, wisdom and a cup of tea as we explore the 7 most likely reasons your cat may have a stubborn closed eye.

The Usual Suspects: Common Causes of a Half-Shut Eye in Cats

When one of your cat’s eyes appears glued shut, you instinctively know it is not normal. Cats depend heavily on their vision to navigate the world and hunt prey. An inability to open one eye all the way points to discomfort, injury or illness resulting in involuntary squinting.

But what motivates a cat to keep their eye clamped closed? Based on veterinary research and clinical experience, these 7 conditions rank among the most common culprits behind a cat with a half-closed eye:

1. The Sneaky Infection – Conjunctivitis

Conjunctivitis is arguably the most prevalent cause of a narrowed cat eye accompanied by other symptoms like ocular discharge. This sneaky infection involves inflammation of the conjunctiva, the protective membrane lining the inner eyelids and whites of the eyes. It strikes when infectious bacteria, viruses, parasites or allergens infiltrate this sensitive tissue, provoking swelling, redness and irritation.

Conjunctivitis often begins in one eye but can spread to both if left untreated. Common infectious culprits behind conjunctivitis include:

  • Chlamydia felis
  • Staphylococcus
  • Streptococcus
  • Herpesvirus
  • Calicivirus

Allergic conjunctivitis can also arise when the conjunctiva reacts to contact irritants like dust, cigarette smoke, pollen or chemicals. Furthermore, dry eye syndrome makes cats prone to conjunctivitis by compromising the tear film barrier against infection.

No matter the cause, inflammation drives the conjunctiva to become engorged with blood and fluid. This prompts involuntary squinting and spasm of the eyelids to shield the eye from light and protect damaged tissue. Thus conjunctivitis rises to the top of the list when evaluating a cat with one eye persistently closed.

2. The Traumatic Injury – Corneal Abrasions and Ulcers

While conjunctivitis stems from microscopic infectious and allergic offenders, obvious physical trauma can also make cats unwilling to open their eyes. Any injury affecting the cornea, the clear outer layer covering the iris and pupil, provokes extreme light sensitivity and blepharospasm (forced eyelid closure).

Corneal abrasions involve superficial scraping away of the corneal epithelium, which contains the sensitive pain receptors. Ulcers go deeper into the corneal stroma, creating open craters that allow fluids to leak and risk infection. Both abrasions and ulcers cause tearing, squinting and forced eyelid closure in an attempt to protect the damaged cornea.

Cats often receive these injuries from minor accidents like scratches from other pets, falls against furniture, or having debris like foxtails get trapped under their eyelids. But the aftermath is major eye pain and involuntary squinting. So corneal damage must also be considered when investigating a half-closed cat eye.

3. The Pressure Problem – Glaucoma

Unlike the two preceding suspects stemming from external factors, glaucoma is an intrinsic condition within the eye causing symptoms like narrowed eyes. In glaucoma, stagnant fluid cannot drain properly from the eye, leading to a dangerous buildup of intraocular pressure.

This pressure compresses the optic nerve and retina, initially killing peripheral vision cells. The increased pressure also causes the eye to appear swollen, inflamed and red. Eye structures stretch and deteriorate under this force, which leads to squinting and eventually blindness if uncontrolled.

Middle aged to senior cats are most commonly afflicted with glaucoma. Burmese cats in particular seem genetically predisposed. Glaucoma can strike suddenly in one eye or gradually worsen over time. Either way, the sustained pressure takes a devastating toll that demands rapid diagnosis and treatment to save vision.

4. The Sneaky Squatter – Eye Parasites

Microscopic organisms like bacteria and viruses are not the only parasitic troublemakers that can take up residence in a cat’s eye. Larger external and internal parasites may also irritate the eyes and cause a cat to keep their eyes clamped closed.

Ocular larva migrans is a condition in which the larval forms of parasitic roundworms, like Toxocara cati, infiltrate the eye. Their migration through the eye tissues provokes severe inflammation, scarring and eye damage.

Thelazia callipaeda, commonly called eyeworms, are nematode parasites spread by flies that feed on eye secretions. These worms cause irritation, infection and ulceration.

Otodectes cynotis, the ear mite, can migrate from infected ears into the eyes, causing itching, crusting and squinting.

So parasitic invaders must not be overlooked when seeking the root of a cat’s eye troubles. A thorough head to tail exam and testing of ocular discharges can help uncover the culprit.

5. The Great Imitator – Horner’s Syndrome

Unlike the previous suspects producing one-sided symptoms from a localized eye problem, Horner’s syndrome generates telltale bilateral signs that can mimic a half-closed eye.

Horner’s syndrome stems from disruption of the sympathetic nerves supplying the eyes and surrounding facial muscles. This impairs nerve signals to the iris sphincter muscle, causing constricted pupils. It also weakens the upper eyelid muscle, leading to drooping.

The affected eye thus appears smaller, sunken in and partially closed. The third classic sign is protrusion of the third eyelid across the eyeball. These characteristic triad of symptoms develop on the side of the nerve injury.

Common causes range from ear infections to trauma, masses or middle ear disease compressing the sympathetic nerves. Horner’s itself does not cause eye pain or vision loss. But it’s critical to identify and address the underlying nerve injury, which may become serious if left unresolved.

6. The Devious Growth – Cancerous Eye Tumors

The most ominous causes of a cat’s closed eye are cancerous tumors affecting the eyelids, conjunctiva, tear glands or eyeball itself. Ocular tumors are somewhat rare but do crop up more often in older cats.

Cancers like squamous cell carcinoma and lymphoma can cause swelling, bulging or ulceration of the eye. Vision loss, reddening of the whites, and abnormal pupil responses may also be seen.

As tumors enlarge, they place pressure on surrounding eye structures. This breeds discomfort and a tendency to keep the cancerous eye closed. Catching ocular cancers early maximizes treatment success before they become invasive or metastatic.

7. The Stealthy Decline – Eye Damage from Systemic Diseases

Finally, we can’t rule out underlying systemic conditions that secondarily afflict the eyes as the reason for a cat’s partially shut eye. Diseases like hyperthyroidism and diabetes can instigate eye issues ranging from diabetic retinopathy to corneal ulcers and glaucoma.

Infections like toxoplasmosis, bacterial bartonellosis and FIV can also manifest with ocular inflammation, compromised vision and light sensitivity prompting squinting. Therefore, illness elsewhere in the body should not be overlooked as possibly impairing delicate eye structures.

Now that we have explored our lineup of usual suspects, how can we determine which one is the perpetrator making your cat refuse to open their eye? Read on for tips on how vets diagnose the root cause and guide appropriate treatment.

Cracking the Case: How Veterinarians Diagnose a Half-Closed Eye in Cats

Which condition explains your cat’s stubbornly shut eye? Conjunctivitis? Corneal damage? Glaucoma? Systemic illness? To unravel this mystery, veterinary ophthalmologists utilize:

The Medical History

Like with any detective work, the case background provides critical context. Your cat’s health history, prior issues, medications, and onset of symptoms help narrow down differential diagnoses. Recently treated diseases, new medication, or changes in diet or environment offer clues about potential allergic or toxic triggers.

The Complete Ocular Exam

Your vet will then perform a meticulous eye exam, aided by an ophthalmoscope, slit lamp, and fluorescein staining. They check:

  • Eyelid position and movement
  • Pupil size and reflexes
  • Intraocular pressure
  • Retinal blood vessel appearance
  • Corneal defects highlighted by stain
  • Presence of foreign material or parasites
  • Discharge, redness and swelling

Like fitting together puzzle pieces, each finding contributes to completing the diagnostic picture.

Advanced Imaging

For internal eye issues or Horner’s syndrome, advanced imaging like CT scans and MRIs visualize the presence or absence of tumors, cysts, inflammation and nerve dysfunction to pinpoint the root cause.

Laboratory Tests

Microscopy, cultures and cytology of discharge can identify infectious organisms. Bloodwork screens for conditions like hyperthyroidism that impact eyes secondarily. Biopsies definitively diagnose cancerous eye tumors.

Once test results are in, your vet can confidently diagnose the condition driving your cat’s half-closed eye. Then they can outline the appropriate treatment plan to relieve symptoms and tackle the underlying problem.

Treating Cats with Persistently Closed Eyes: Resolving the Root Issue

With the culprit identified, treatment can be initiated to coax your cat’s eye open again and cure any associated illness. Treatment strategies vary based on the diagnosis:


  • Antibiotic or antiviral eye drops/ointment
  • Oral antibiotics for stubborn bacterial infections
  • Artificial tears for dry eye triggers
  • Steroids and antihistamines for allergies
  • Elizabethan collar to prevent pawing and rubbing

Corneal Injuries

  • Antibiotic and anti-inflammatory eye drops
  • Oral pain medication
  • Elizabethan collar
  • Corneal debridement and surgical repair if needed


  • Medicated eye drops to reduce internal eye pressure
  • Oral carbonic anhydrase inhibitors
  • Surgery like goniotomy or enucleation if drugs fail

Eye Parasites

  • Topical and oral deworming medication
  • Rinsing eyes to mechanically remove parasites
  • Antibiotics for secondary bacterial infection
  • Anti-inflammatory medication
  • Elizabethan collar

Horner’s Syndrome

  • Addressing underlying nerve injury
  • Eye drops to constrict normal eye pupil
  • Allowing natural recovery of nerve function

Eye Tumors

  • Surgical excision
  • Cryotherapy
  • Radiation therapy
  • Enucleation if cancer is untreatable

Systemic Diseases

  • Treating the primary condition like hyperthyroidism or diabetes
  • Symptomatic care like lubricating drops
  • Addressing any secondary eye damage

With diligence and patience, most causes of a narrowed cat eye can be successfully overcome. But some conditions like glaucoma or eye cancer may have a guarded long-term prognosis. Discuss expected outcomes realistically with your vet.

At-Home Nursing Care for Cats with Half-Closed Eyes

Your job as a cat-sleuth is not done once your cat is diagnosed and on prescribed treatment. Meticulous at-home care improves comfort, speeds healing and catches any setbacks promptly:

  • Administer all eye medications and treatments exactly as the vet instructs
  • Gently clean any crusty discharge away from eyelids daily
  • Apply warm, moist compresses to affected eyes for 10 minutes twice daily
  • Monitor appetite and litter box habits to ensure normal eating, drinking and elimination
  • Limit activity and prevent trauma to injured or infected eyes
  • Keep Elizabethan collars on determined pawers and rubbers
  • Report any worsening of the condition or new symptoms to your vet
  • Do not miss follow up exams until the eye is fully healed

With diligent observation and care on your part, your cat’s eye troubles can soon resolve and their world open up again. But be sure to remain vigilant for potential relapses like viral conjunctivitis flaring up again.

When to Seek Emergency Ophthalmic Care

While many cat eye conditions can be managed on an outpatient basis, certain situations demand urgent vet attention to prevent permanent damage. Rush to emergency or specialty ophthalmic care if your cat has:

  • Sudden complete vision loss
  • Rupture or collapse of the eyeball
  • Uncontrolled bleeding inside the eye
  • Severe swelling or bulging of the eye
  • Corneal ulceration with significant leakage of ocular fluid
  • Pupils fixed and unresponsive to light
  • Infection rapidly spreading to both eyes
  • Excessive pawing that may further injure the eye
  • High risk for self-trauma if left unmonitored

Don’t delay when it comes to emergency care for acute eye injuries and illness. TheDifference between saving vision and blindness may be a matter of hours.

The Take-Away: Keep a Watchful Eye on Your Cat’s Eyes

As we have explored through this feline eye investigation, a wide range of conditions can cause a cat to stubbornly keep one eye closed. It takes a methodical gathering of clues and definitive diagnostic testing to pinpoint the precise perpetrator. Harness your inner detective to monitor your cat’s eyes closely for any abnormalities. Then work hand in hand with your vet to uncover the cause and plot an effective treatment plan when you notice an issue. With patience and persistence, you can prevail over whatever is ailing your cat’s eye and help them see the world clearly again.