What is coloboma?
Coloboma (pronounced "kah-luh-BOW-muh") is a condition characterized by missing tissues in and around the eye. The condition is present at birth and is caused by abnormal development during gestation.
Coloboma is derived from the Greek word for “curtail” or reduce. People with coloboma eyes are born with certain tissues missing, leaving gaps or notches in part of the eye’s structure.
A fetus’ eyes form and develop throughout the first three months of pregnancy. During this time, a seam known as a choroidal fissure (also called the optic fissure or embryonic fissure) connects and secures to form the structure of the eye.
Typically, this connection occurs between week five and week seven of pregnancy. If the choroidal fissure fails to close by the end of week seven, a gap or coloboma is left. The location of these gaps in the fissure determines where the colobomas are located.
This condition can be inherited or happen spontaneously, and can affect one or both eyes. It is believed that genetic defects or chromosomal abnormalities are the most likely cause.
For instance, colobomas are often seen in cases of CHARGE syndrome, which is known to affect gene CHD7. However, the specific genes involved in coloboma are still unknown.
It’s also possible that environmental conditions and maternal health play a part in the development of coloboma, specifically when alcohol is consumed during pregnancy. Research shows coloboma as a “key malformation” seen in infants with Fetal Alcohol Syndrome.
Typically, infants with Fetal Alcohol Syndrome also exhibit other symptoms of the condition, such as low birth weight, deformed joints, limbs or fingers, and hearing difficulties.
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Types of eye colobomas
Colobomas can affect several parts of the eye, including the eyelid, iris (colored part of the eye), retina, optic nerve, lens and macula.
It is common for multiple coloboma types to be present in conjunction with one another. For example, a child may be born with eyelid coloboma and retinal coloboma.
Eyelid coloboma refers to missing or incomplete eyelid tissue, which happens when the skin folds of the eyelid fail to fuse together. Results can be minor, where the lower eyelid appears uneven or droopy, as if melted, or where the edges of the eyelids look incomplete, or severe enough that half of the upper eyelid is missing.
The condition is rare — affecting one in every 10,000 births — with gender or race having little to no impact on risk.
Eyelid coloboma may affect only one eye (unilateral coloboma), though cases have been reported where both eyes show symptoms (bilateral coloboma). The condition may also affect anywhere from one eyelid, to all four (upper and lower lids of each eye).
Severe cases of eyelid coloboma may require surgical treatment to create or complete an eyelid. Other treatment involves patches, moisture chamber eye bandages, artificial tears and ointments to protect the eye and keep it moist — a task typically performed by the eyelids.
Iris coloboma (also called uveal coloboma) is characterized by having a gap in the colored part of the eye.
This often looks like a black notch on the pupil that extends or drags to the edge of the iris, giving individuals a cat-eye appearance. In fact, iris coloboma appears in another genetic condition called cat eye syndrome, named specifically for the rare feature.
While an iris coloboma can make the pupil appear irregularly shaped, people with this condition have normal-sized, regularly functioning pupils. It’s possible for minor vision issues to occur as a result of iris coloboma, including refractive errors.
Corrective glasses or contact lenses can successfully treat any refractive errors associated with iris coloboma. Though a surgical procedure is available to repair the iris, colored contact lenses can also be used to hide or cover the coloboma, creating the appearance of an average eye.
Aniridia is a condition similar to iris coloboma in that it creates a partial or complete absence of the iris, but in these cases, it results in pupil abnormalities, low visual acuity and sensitivity to light (photophobia).
SEE RELATED: Polycoria: Multiple pupils in one eye
Retinal coloboma happens when the choroidal fissure gap occurs toward the back of the eye. This is where light-sensitive retinal tissue is located, as well as the choroid (blood vessels that line the inside of the retina). Coloboma in this area results in missing retinal tissue and blood vessels.
While the retina is vital for clear vision, it’s possible for people with retinal coloboma to show no symptoms. However, certain complication can result from the condition, including:
Loss of visual clarity
Retinal tear or detachment (can occur at any age)
Abnormal blood vessel growth around the choroid
Retinal coloboma may affect one or both eyes. It is not typically diagnosed at birth, as the retina is an internal structure and undetectable from outside observation.
Treatment for retinal coloboma may not be necessary if the individual experiences no symptoms or complications. However, surgical treatment may be required for retinal detachment, cataracts, glaucoma and abnormal blood vessel growth.
Optic nerve coloboma
Optic nerve coloboma (also called optic disc coloboma) occurs when there are gaps or holes in the structure of the optic nerve. The optic nerve works by sending images created by the eye to the brain, making it critical for clear vision.
Depending on the size and location of the coloboma, symptoms range from complete vision loss to no detectable symptoms at all.
Like retinal coloboma, optic nerve coloboma is not usually detected without an eye exam. Though there is no treatment for optic nerve coloboma, low vision aids can help people whose eyesight has been affected by it.
Treatment options depend on the type of coloboma that you have. It’s also possible to live with mild coloboma your entire life and never experience complications or require treatment.
For those looking for coloboma treatment, successful methods for each type include:
Eyelid coloboma — May be treated surgically or managed with products designed to protect and moisten the eye.
Iris coloboma — Can be surgical treated by having the iris sutured, essentially closing the gap. Less invasive option includes wearing color contact lenses to cover the coloboma.
Retinal coloboma — Surgical procedures are available to treat complications associated with retina coloboma, including cataracts, glaucoma and retinal detachment.
Optic nerve coloboma — No treatment is available to treat optic nerve coloboma. Low vision aids are available to help those whose vision has declined due to the condition.
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When to see an eye doctor
As mentioned previously, some people never experience complications related to coloboma. However, if you notice any of the following symptoms, you should see an eye doctor quickly:
Eye pain, redness or cloudiness
Shadows or dark spots in your visual field
Sudden development of (or increase in) eye floaters
Severe headaches, nausea or vomiting
Flashes of light that are not produced by an outside source
Sensation that a dark curtain is interfering with the corners of your visual field
READ MORE: Rare eye diseases: What causes them and how are they treated?
Page published on Wednesday, January 27, 2021