What Is Coloboma?

Coloboma is a congenital (present at birth) abnormality of the eye. Colobomas are missing pieces of tissue that may appear as gaps or notches. When coloboma affects the iris, it manifests as a keyhole or cat-eye appearance of the pupil. Coloboma is estimated to affect 1 in 10,000 people. The condition does not always change the appearance of the eye, nor does it, in every instance, impact a person’s vision. Therefore, it is thought that it is likely undiagnosed in some people.

Colobomas may involve one or several structures of the eye, including:

• Iris: The iris is a round, disk-shaped muscle with a hole in the middle where the pupil is located. It is the colored part of the eye responsible for allowing the right amount of light to reach the retina. The iris controls the light that enters the retina by changing the size and diameter of the pupil. Coloboma of the iris does not usually cause visual impairment, but it may result in sensitivity to light.
• Retina: Specialized tissue that lines the back of the eye, the retina senses light and creates electrical impulses which are sent to the brain via the optic nerve. Microphthalmia (small eye) is often linked with very large colobomas of the retina.
• Choroid: The blood vessel layer of the eye, located between the retina and the sclera (the white outer coat that surrounds the iris)
• Optic nerve: A bundle of over a million nerve fibers that carry visual messages from the retina to the brain. Coloboma of the optic nerve often causes blurry vision and blind spots.

Coloboma Symptoms

Symptoms of coloboma may include:

• Missing pieces of tissue in one or more structures that form the eye (the iris, choroid layer, optic nerve or retina)
• A keyhole or cat-eye appearance of the pupil (when the coloboma affects the iris)
• Missing pieces of tissue in one or both eyes
• Sensitivity to light
• A noticeable defect or notch in the eyelid (as a result of eyelid colobomas)
  It’s important to distinguish colobomas of the eyeball from gaps that occur in the eyelids (which are also referred to as colobomas). But eyelid colobomas arise from abnormalities in different structures than eyeball colobomas, during fetal development.
• Vision impairment (depending on the size and location of the coloboma)
• A field defect (vision loss in a certain part of the visual field, such as the upper visual field). This is usually a result of colobomas that impact part of the retina.
• Reduced vision involving the inability to correct vision with corrective lenses; this is usually a result of colobomas affecting the optic nerve.

Coloboma often accompanies other conditions of the eye including:

• Cataracts (clouding of the lens)
• Myopia (nearsightedness)
• Nystagmus (involuntary eye movements)
• Glaucoma (increased pressure inside the eye that can damage the optic nerve)
• Microphthalmia (one or both eyeballs are abnormally small)
• Retinal detachment (separation of the retina from the back of the eye)

Colobomas can occur alone (called non-syndromic or isolated colobomas) or they can be part of a syndrome that impacts other organs and tissues (called syndromic colobomas).

Causes

The cause of coloboma is abnormal development of the eye in utero (in the womb), specifically, during the second month of fetal development. The defect is a result of a seam (called the optic fissure) failing to close properly during fetal development. The optic fissure forms the bottom portion of the eyeball during fetal development; this is why colobomas transpire in the lower part of the eye. The exact structure in the eye that ends up being impacted by the coloboma depends on the section of the optic fissure that didn’t close properly.

Genetic Impact

Changes in genes that impact the early development of the eye may be linked with coloboma. In fact, according to the Genetics Home Reference, many of these genes have been identified, but only in a very small number of people. More studies are needed to definitively link specific genetic defects with the development of coloboma.

Environmental Factors

Environmental factors (such as maternal alcohol use during pregnancy) may increase the risk of coloboma in the fetus.

Diagnosis

An ophthalmologist will use a tool called the ophthalmoscope to exam the infant’s eyes when coloboma is suspected. As a child gets older, other tests may be conducted to measure the scope and severity of the problem. These tests may include visual acuity tests (to measure the presence and severity of visual loss).

Treatment

Although there is not presently a cure for coloboma, there are some treatment options available. For those with vision impairment, treatment aims to help a child adjust. Some of the associated conditions of coloboma (such as cataracts) can be treated. Treating cataracts, glaucoma, or other associated eye conditions will help to improve vision problems, but will not completely solve the problem.

Treatment for colobomas that affect the iris can help it to appear normal. This may involve a colored contact lens or lenses (when both eyes are affected) to make the iris look as though it is round. There is also a surgical procedure that can be done to correct the appearance of the iris.  Those with coloboma of the iris may benefit from wearing tinted glasses to help with sensitivity to light.

Several procedures are possible to repair colobomas of the eyelid. 

Vision Problems

Treatment for those with vision problems from coloboma may include:

• The use of low vision devices (such as and-held magnifiers, strong magnifying reading glasses and more) and vision rehabilitation services (services that help people with low vision to live as independently as possible and to maintain a high quality of life)
• Treating lazy eye in children
• Treating microphthalmia in children
• Treating co-existing eye disorders, such as cataracts, glaucoma, or retinal detachment

Preventative Treatment

Preventative treatment to prevent lazy eye (for a child with coloboma in just one eye) may involve treatment to the unaffected eye such as:

• The use of a patch
• Special eye drops
• Glasses

According to the American Academy of Opthalmalogy, "Sometimes this treatment [eye patch, eye drops or glasses for the unaffected eye] can improve vision in eyes even with severe colobomas."

Coping

If you have a child who has been diagnosed with coloboma, you probably know that it is a natural instinct to worry about your child. Your child may have normal vision, or some vision loss, but you may still be concerned about what the future holds. Staying abreast of the latest in education about the coloboma, as well as being familiar with current medical research studies, reaching out for support from other parents, and engaging in formal support systems (such as individual or group therapy) can help. 

One of the best ways to help a child with coloboma is to be sure to keep regular eye clinic appointments and eye examinations. Keeping up with your child's regular eye screenings will improve the chances of early detection when new problems arise. Finding any problems, or detecting a decline in your child's vision early on will engender the best long-term outcome possible.

Online support services to check out include:

• Enroll in a parent tele-support group (for parents of children who are visually impaired).
• Learn about available healthcare services for the visually impaired.
• Learn about new clinical research trials for people with coloboma.