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At a glance
About: The third eyelid is an opaque membrane underneath the outer eyelids which protects the cornea.
Causes of a visible third eyelid:
Diagnosis: A thorough physical and ophthalmologic examination as well as diagnostic testing.
Treatment: This will depend on the underlying cause.
What is the third eyelid?
Also known as a haw, nictitating membrane or Tertia palpebra, the third eyelid (TE) is an opaque membrane that is located under the outer eyelids in the inside (medial) corner of the eye. The purpose of the third eyelid is to extend across the eye to protect the cornea from scratches and wipe away dust and debris. When the cat blinks, the third eyelid sweeps across the eyeball like a windscreen wiper. The third eyelid gland is responsible for tear production, to lubricate the eye.
Structures which make up the third eyelid include the triangular membrane, t-cartilage and third eyelid gland.
What does it mean if the third eyelid is visible?
A visible third eyelid can affect one eye (unilateral) or both (bilateral). Anything which causes the eye to sit deeper in the orbit will make the third eyelid visible.
Conjunctivitis, uveitis, glaucoma or corneal ulcers can cause the extraocular muscles to contract, which sinks the globe into the orbit, which causes the third eyelid to protrude.
Also known as pink eye, conjunctivitis is an inflammation of the conjunctiva, the pink membrane which covers the front of the eyeball and inside the eyelids. Inflammation can lead to hypertrophy (increase in size) of the third eyelid.
Conjunctivitis 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.
A neurologic disorder caused by loss of sympathetic innervation to the eye which is responsible for glandular and involuntary functions.
This non-painful disorder causes contraction of the pupils, drooping eyelids, retraction of the globe and visible third eyelid.
Prolapse of the third eyelid gland which is at the base of the third eyelid due to a weakness of the gland’s attachment in the cat’s eye. Cherry eye can occur in any breed of cat; however, there is a higher incidence in Burmese cats.
Grass seed, dust or other debris lodged behind the eyelid can cause swelling and inflammation of the third eyelid.
Tumours of the third eyelid gland are rare in cats; the most common causes are adenocarcinoma, followed by squamous cell carcinoma.
Also called Key-Gaskell syndrome, dysautonomia is a rare condition of the sympathetic and parasympathetic nervous systems which work in harmony to prepare the body for fight or flight (sympathetic) or relax the body (parasympathetic). The disease is caused by non-inflammatory destruction of the autonomic ganglia which are a cluster of nerve cell bodies in the autonomic nervous system.
Tetanus (lockjaw) is a disease caused by the bacteria Clostridium tetani. The bacteria produce a neurotoxin (tetanospasmin toxin) which causes painful muscle contractions and spasms. The bacteria are present in soil, manure and the intestinal tracts of many animals, where it does not produce disease. They are obligate anaerobes, (which means they live in conditions where there is little to no oxygen), in warm-blooded animals.
A rare disease which is thought to be an autonomic imbalance due to gastrointestinal inflammation or disease. Causes include torovirus, dietary hypersensitivity, inflammatory bowel disease, pancreatitis and tapeworm infection.
Fat or muscle atrophy:
As the cat ages, fat and muscle can atrophy (shrink) which changes the position of the eye within the orbit, which makes the third eyelid more visible.
Reduced body fluid can cause enophthalmos (a recession of the eyeball into the orbit), which can lead to protrusion of the third eyelid. Dehydration can be due to inadequate water intake or fluid loss due to vomiting, diarrhea, diabetes and kidney disorders.
The veterinarian will perform a complete ophthalmological and physical examination of the cat and take a medical history from you. Accompanying symptoms as well as bilateral or unilateral presentation may provide the veterinarian with a possible cause.
- Baseline tests: Complete blood count, biochemical profile and urinalysis to evaluate the overall health of the cat, including kidney function and blood sugar levels.
- Fine needle aspirate: The veterinarian inserts a needle into the third eyelid to obtain a sample, to evaluate under a microscope.
- Phenylephrine test: This medication is applied to the eye to determine if the pupil dilates after application; this helps the veterinarian evaluate the sympathetic nerve passage for cats with suspected Horner’s syndrome or dysautonomia.
- Schirmer tear test: To measure the level of tear production. A commercial filter strip is placed under the lower eyelid for 60 seconds. The moisture from the eye will slowly descend the strip and the level of moisture measured in mm, which can be diagnostic for dysautonomia.
- Fluorescein staining: A fluorescein stain is placed in the eyes to look for ulcers or foreign bodies.
- Tonometry: Measurement of the pressure within the eye for cats with suspected glaucoma.
- Third eyelid examination: The veterinarian will administer a local anesthetic and carefully evaluate the third eyelid with the use of forceps.
- Ophthalmoscopy: An examination of the back part of the eye.
- Xrays: Chest xrays for will be necessary for cats with neoplasms to evaluate for signs of metastasis.
Surgery to return the gland to its normal position. Incisions are made on the edge of the gland in the conjunctiva, which is buried in the pocket with the conjunctiva placed over the top.
Find and treat the cause of dehydration as well as provide supportive care which will include fluid therapy. Long term management of kidney disease such as low-protein diet,
Find and treat the underlying cause, which may include anti-inflammatories, medications to bring down the intraocular pressure and analgesics to relieve pain.
Acepromazine is a sedative which is administered as part of the anesthetic protocol or anxiety, can lead to bilateral elevation of the third eyelid due to a decrease in orbital muscle tone.
In most cases, no treatment is necessary, and it will resolve within 4-8 weeks. Dewormer if the cat has tapeworm infection.
Antibiotic therapy as well as supportive care which can include sedatives to control spasms, muscle relaxants, soft bedding to prevent bedsores and keep the cat in a dark, quiet room to avoid over-stimulation.
Treatment will depend on the type of tumour and may include surgical removal, radiation therapy and cryotherapy. The outlook for cats with tumours of the third eyelid gland is poor good due to the high rate of metastasis (spread) and cats typically survive 1 to 2 months.
Most cases will resolve on their own. Eye lubricants to maintain adequate lubrication of the eye if the cat is unable to blink normally.
Fat or muscle atrophy:
No treatment is necessary.
Treatment for conjunctivitis will depend on the underlying cause which can include oral or topical antibiotics, antivirals, supportive care and removal of the discharge.
The veterinarian will administer a local anesthetic to numb the eye and remove the foreign body or flush it out.