Coloboma in Cats - Causes, Treatment and Associated Conditions

Key takeaways

A coloboma, sometimes called a “hole in the eye,” is a congenital condition where tissues in one or more structures of the eye fail to form properly.

Eyelid colobomas involve a portion of the eyelid being absent, impacting function
Ulceration, scarring, and infection of the eye are common, and chronic irritation may lead to blindness
Diagnosis requires an ophthalmologic exam
Temporary relief involves eye drops and medications
Treatment includes surgery to repair the eyelid or remove irritating hair
Prognosis depends on the severity of the defect and condition of the eye at the time of treatment
Iris colobomas refer to a thin area of - or a hole in - the iris
The thin or absent tissue causes light sensitivity but does not affect vision
There is no treatment available for iris colobomas, and quality of life is rarely affected

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A closer look: Coloboma in Cats

Colobomas are uncommon in cats and may go undetected by pet parents. Colobomas of the iris or eyelids are more likely to be visible externally while those of the internal structures are harder to detect.

Iris colobomas appear in the iris; the colored portion of the eye. Presentation ranges from one or more small black dots, wedge shapes facing in towards the pupil, to a “notch” radiating outward from the pupil. In severe cases the coloboma is so large the animal appears to be missing an iris. Iris colobomas are easier to visualize in individuals with lighter colored eyes, but occur regardless of eye color.

Lid coloboma appearances range from oddly shaped eyes due to a complete lack of eyelids, to eyes that are normal in appearance with hair growing in towards the eye, and many variations in between. The wide range of presentation is due to differences in how much of the eyelid tissue is missing, what section is it absent from, and if the eyelid is able to roll under itself allowing hair to irritate the eye.

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Risk factors

Iris colobomas are uncommon in cats. When present, iris colobomas have minimal impact on vision and do not change over time. Despite this, iris colobomas are associated with other ocular conditions, such as cataracts, so veterinary attention is warranted.

Eyelid colobomas are also uncommon, although observed more often in certain breeds. Professional assessment of eyelid colobomas is recommended as chronic eye irritation leads to corneal abrasions, conjunctivitis, scarring, ulcers, hyperpigmentation, vascularization, and eventually blindness.

Possible causes

Colobomas are due to genetic defects interfering with development of the affected structures. The exact genes responsible for these defects is currently unknown. Multiple kittens from the same litter may be affected, and these defects are commonly observed along with other eye problems.

Main symptoms

Colobomas are a physical abnormality which may have no symptoms other than the obvious visible signs.

Testing and diagnosis

Colobomas are diagnosed with a general physical exam and a specialized ophthalmologic exam, which includes:

Fluorescein staining of the eyes
Dilation of pupils
Measurement of tear production (Schirmer tear test)
Measurement of pressure inside the eye (tonometry)

Steps to Recovery

Iris colobomas have no treatment options. It is useful to be aware of their presence as difficulty seeing in bright environments can lead to animals wandering into unsafe areas.

Referral to veterinary ophthalmologists is common when lid defects are present, as surgical treatment of the condition is specialized.

Treatments for temporary relief of lid defects include:

Artificial tears ointment
Medication (antibiotics, analgesics)
Manual plucking of hairs that poke or rub the eye

Note: always consult a veterinarian before using topical over the counter medications for pets. Never try to pluck or tweeze eye hair without veterinary guidance. Tools like tweezers may cause severe damage to the eye if they come into direct contact with the eyeball. Manual eyelid hair removal is best performed by a professional, especially if the animal is unfamiliar with the treatment.

Long-term treatments of lid defects include:

Surgical reconstruction
Permanent hair removal (Cryoablation)
Filler injection

Colobomas are permanent.

Iris colobomas impact health and quality of life minimally, if at all.

Lid coloboma prognosis depends on the severity of the defect, type of treatment, and the presence of associated conditions.

In severe cases ocular irritation persists regardless of treatment. Multiple corrective procedures may be necessary to make the cat more comfortable, but if complete correction is not possible, progressive inflammation may eventually cause blindness.

Prevention

Colobomas are genetic and can not be prevented. Cats with colobomas commonly pass the defect onto their offspring, and the severity of deformity in offspring is unpredictable. Avoiding breeding of cats with existing colobomas prevents passing the gene between generations, but the condition can still occur spontaneously whether the breeding parents have a known incidence of coloboma or not.