A coloboma is a congenital condition where one or more structures in or around the eye fail to develop. The part that fails to develop is usually on the lower part of the eye. Coloboma is a Greek word that means ‘defect,’ ‘mutilated,’ or ‘curtailed.’ The eye of a fetus develops rapidly during a pregnant woman’s first trimester. A choroidal fissure develops at the base of the stalks which ultimately forms the eye. The choroidal fissure is supposed to close by the seventh week of pregnancy. Failure to this is what gives rise to a coloboma.
A coloboma can be small or large. It can be unilateral (in one eye) or bilateral (in both eyes). Both eyes are affected in the same way or differently. Also, vision impairment caused by a coloboma may not be evident at birth. The degree of visual impairment caused by a coloboma depends on which structures of the eye are affected.
- Lens coloboma – A part of the lens is missing
- Uveal or Iris coloboma – Coloboma affects the iris causing the appearance of a keyhole or cat-eye
- Macula coloboma – The macula fails to develop as it should
- Eyelid coloboma – Part of the eyelid (upper and lower) is absent
- Chorioretinal coloboma – A missing part of the retina
- Optic nerve coloboma – The optic nerve has space, reducing vision
Causes and Risk Factors
A coloboma may be a genetic disease, passed on by parents. It could also be a result of a genetic syndrome like the cat eye syndrome which is a rare disorder.
Not all coloboma cases are genetic. Some appear by chance in certain babies. Sometimes, a coloboma may be caused by the use of certain drugs or infections during pregnancy. Other causes include trauma to the eye and eye surgery.
Signs & Symptoms
Coloboma symptoms depend on the type. The symptoms may include:
- Iris coloboma – The pupil has the appearance of a cat’s eye. Traumatic iris coloboma can occur after an accident where the iris is ruptured or after glaucoma surgery
- Eyelid coloboma – There will be a bent, defect or notch in the eyelid
- Macula or optic nerve coloboma – The individual will have reduced vision
- Chorioretinal coloboma – There is no vision in a specific location
- An individual with a coloboma that affects the front part of the eye may have issues with vision
- Generally, there may be increased sensitivity to light and loss of vision
An eye care professional will conduct a thorough eye examination. He/she will use an ophthalmoscope to check the inside of an individual’s eye. Later on, other tests like the visual acuity test may be performed. These tests help to check the effect coloboma has on vision.
Treatment of a coloboma aims to correct the specific issue affecting it and to improve vision.
A coloboma has no cure. Treatment depends on the type of coloboma.
- Individuals with iris coloboma can use prosthetic contact lenses which make the iris appear round. They can also use light protection spectacles to help with symptoms like glare or reduced contrast vision. The patient may use spectacles with blue blocking filters.
- Low vision devices can help people with other types of coloboma.
- The eye doctor will help the patient manage the conditions that develop as a result of a coloboma. The conditions include cataract and the growth of new blood vessels in an aging eye.
- The doctor may recommend specific treatment if the coloboma affects one eye. He/she can also put a patch or recommend special eye drops or glasses in the eye that has not been affected by a coloboma. The doctor does this to prevent the development of amblyopia (lazy eye).
Surgery can correct the appearance of an iris to correct iris coloboma. An artificial intraocular lens with the iris painted on can be implanted in a patient. An artificial iris tissue, custom-made from silicon, can also be implanted. A third implant option is a foldable artificial iris. Surgery can also be used to repair coloboma of the eyelid.
Both children and adults with iris coloboma have reasonably good vision. However, they may develop photophobia (sensitivity to light).
People with lens coloboma may develop a cataract. Cataract clouds vision since the lens gets cloudy giving rise to blurry images.
Individuals with chorioretinal or optic nerve coloboma may have a poor central vision which can affect daily activities like reading and driving.
People who have bilateral optic nerve coloboma may develop nystagmus, a condition in which the eyes move uncontrollably.
Coloboma increases the risk of other eye diseases such as retinal detachment, glaucoma and choroidal neovascularization. Others include strabismus, microphthalmia (a very small eye) and blind spots in the field of vision.
People with a coloboma need regular eye checkups in case of any changes that might affect vision.