Coloboma is a condition affecting the eye. It is a congenital condition, which means it is present at birth. The defect can be inherited or the result of something that went wrong during the pregnancy while the eye was developing. Less than one in 10,000 babies are born with a coloboma.
Definition & Facts
Coloboma is derived from koloboma, the Greek word for “defect” or “curtailed.” A person with coloboma has something missing in the structure and tissues of one or both of their eyes. Both eyes can be affected the same way or each eye can have a different type of coloboma. As of 2016, there is no cure for coloboma.
Colobomas can present as a hole in the iris, which is the colored part of the eye or a hole in the retina, which is the back part of the eye that is sensitive to light. The macula, which is the center of the retina responsible for fine central vision and color vision, can also be affected.
Colobomas can affect the choroid, which is the blood vessel-filled layer beneath the retina. The optic nerves can be affected. These nerves transmit signals to the brain which allows the person to see. A classic coloboma is a keyhole-shaped defect in the iris. The keyhole may be so small that it is unnoticed and does not affect the person’s vision.
Many people with coloboma also have unusually small eyeballs. In some cases, the eyeball is so small that it appears to be missing. A small eyeball does not necessarily lead to vision loss.
Coloboma is associated with other conditions. Some of these conditions, such as cataracts, glaucoma, retinal detachment, nearsightedness, and irises of different colors, affect the eye. Other conditions that appear with coloboma affect other organs in the body. When coloboma appears with these other disorders, it’s considered syndromic. CHARGE syndrome is a condition seen in newborns. This syndrome arises due to a genetic mutation of the CHD7 gene. The coloboma is accompanied by congenital heart defects as well as defects of the nasal cavity, genitals, and ears.
Holes or gaps in the eyelids are also called coloboma, but they aren’t caused by the same processes that cause defects in the eye itself.
Symptoms & Complaints
If the hole is found in the retina, the patient can lose sight in the upper parts of their visual field. If the optic nerves are affected, the person often has such poor vision that it can’t be helped by contact lenses or glasses. Some children with colobomas are sensitive to light. A child with a coloboma in one eye might be at risk for amblyopia or lazy eye.
Coloboma occurs when the optic or choroid fissure does not close up properly while the baby is in the womb. The eyes begin as two stalks that emerge from the brain. The undersides of these stalks have fissures that will hold blood vessels. They must begin to close up by the fifth week of pregnancy and should be completely closed by the seventh week. Where the defect appears in the eye depends on which part of the fissure did not close properly.
In some cases, mutated genes are responsible for the coloboma, including genes that are found on the X chromosome. Colobomas caused by mutations on the X chromosome are more severe in boys than in girls. Mutations that are known to be associated with colobomas affect the GDF3 gene, GDF6 gene, OT2 gene, SHH gene, VSX2 gene, and PAX6 gene.
Depending on the genetic mutation involved, coloboma can be inherited in an autosomal dominant inheritance pattern, an autosomal recessive inheritance pattern, an X-linked dominant inheritance pattern or an X-linked recessive inheritance pattern. A fetus that’s exposed to toxins like alcohol may be more at risk of developing the defect.
Diagnosis & Tests
If a baby is suspected of having a coloboma, an eye doctor uses an ophthalmoscope to examine their eyes. When the child is old enough, they are given eye examinations and vision tests to see if and how their vision is affected by their coloboma.
Treatment & Therapy
Eye surgery can correct a coloboma in the iris. Cosmetic surgery can be used to repair coloboma in the eyelids. Patients can also volunteer to participate in clinical trials. The patient’s ophthalmologist should monitor the eye for signs of co-morbidities such as glaucoma, cataracts or retinal detachment.
The eye doctor may put a patch over the eye, prescribe medications, or recommend special glasses - all with the goal of strengthening the child’s overall vision. Patients with low vision can be helped with occupational therapy and low vision aids. If there is a blind spot in their field of vision, they can be taught to find their preferred retinal locus, or PRL (in which a person uses a different part of their eye to compensate for their vision loss). They are taught to organize their environment so that there is a designated spot for everything, from groceries in the refrigerator to car keys to clothing.
People with colobomas also benefit from improved task lighting and contrast, and decreased glare, which may be as simple as covering a shiny countertop with a cloth or wearing sunglasses with yellow lenses. They are taught to sit close to things they want to see; buy items with unusually large letters, numbers or characters; and make use of audio books and voice interface systems. Magnifying glasses may be useful for people with a coloboma that affects their vision.
Prevention & Prophylaxis