Coloboma: A Rare Birth Defect

The term ‘Coloboma’ in the Greek means ‘unfinished.’ Essentially, Coloboma occurs when the eye stops growing before it is fully developed.

If you haven’t heard of it, you’re not alone. Coloboma is a very rare congenital disability. It is a gap in the eye’s structures. Large or small, the difference can occur in various areas of the eye such as the eyelid, iris, ciliary body, lens, retina, macula, choroid and optic disc. People with Coloboma may appear as though the pupil(s) of their shape of the eye(s) is like a keyhole or notch. It can give the eye a split iris effect or appear as merely a black notch. Some refer to the eyes’ appearance as ‘cat eyes.’

How the Eye is Formed

Our eyes are formed in the womb, starting as a small bud and then sprouting outward to develop all the intricate parts of the eye. It occurs during the fourth and fifteenth week of pregnancy. Although the eye begins to form early on, the formation may not be complete until the later stages of pregnancy. Near the beginning, there is a development in the gap called the optic fissure which brings nourishment to the eye. It opens on the underside of each bud. This gap closes once the formation of the eye completes.

What causes Coloboma?

Genetics are a possibility; however, there are instances where Coloboma appears without any previously known family history of the disease. It is termed ‘sporadic.’ As the eye forms, if the fissure does not close completely, Coloboma has occurred. The gap will remain throughout life.

Effects on Vision

What we see is made in the brain from electrical signals provided by our eyes. If we didn’t get the signals correctly, we have poor vision. For some people, Coloboma does not affect their vision; for others, vision can be significantly affected. Many times if both eyes are affected, blurred vision occurs. However, that is not always the case. For some, sensitivity to bright light is their only concern, outside of the apparent cosmetic effect. For others, blindness occurs. The degree of vision impairment, from mild to severe, rests on how thoroughly the eye has formed.

Case Studies in Coloboma

Rachel has bilateral Coloboma. One eye has a ‘keyhole’ effect, and the other isn’t as pronounced. Thirteen years ago, she was born squinting. Her mother noticed she had ten fingers, ten toes, looked normal, except for the perpetual squint. She wasn’t too concerned, figuring Rachel had not adjusted to being out in the light. Newborns’ eyes don’t open all that wide anyway, what with their chubby cheeks, so she didn’t notice at first that her eyes were different. Once she did, Rachel’s doctor told her to contact an opthalmologist. That’s how she first heard of Coloboma, and that’s how she first learned that her baby daughter had a congenital disability. As you can imagine, she wanted to know what this meant, and how it would affect her daughter’s life.

Casey also has Coloboma. Her left eye is affected to the point where she is blind in that eye. Also, she has had brachial clefts in her neck and had problems with hearing, speech, and learning capacity. Casey’s schedule consists of occupational therapy, physical therapy, and speech therapy. She is now in a pre-K program designed for special needs kids. Her parents face Coloboma head on every day and struggle with the effects it has had on their daughter.

Fortunately, Rachel’s vision is normal.  However, she is sensitive to light and wears sunglasses during the summer. Her eyes allow more light, causing sensitivity. On the other hand, Rachel sees better than those of us with healthy eyes in the dark. Her mother recounted a time when she was three, looking out their front door, fascinated. She looked and didn’t see anything. Rachel insisted there was a dog outside. Sure, enough, when her mother turned on the porch light, where he was.

Most children with bilateral Coloboma have blurred vision. However, those with only one eye affected (unilateral Coloboma), usually have a right image in the unaffected eye.

How many people have Coloboma?

Coloboma occurs in 1 of every 10,000 people. Interestingly, 80 to 90% of children diagnosed with CHARGE have Coloboma. CHARGE is an acronym for a group of developmental abnormalities:

C– Colobomas and Cranial Nerves

H– Heart problems

A-  Atresia of the choanae (blocked or narrow nasal passages)

R- Retardation of Growth

G- Genital and urinary abnormalities

E– Ear and hearing abnormalities

Fortunately, this genetic condition is extremely rare in patients diagnosed with Coloboma. Determining this disorder can be difficult as these symptoms can manifest in other disorders as well, such as Delleman syndrome and Wolf-Hirschhorn syndrome, also rare genetic disorders. A great percentage of children diagnosed with CHARGE have an alteration in the CHD7 gene located on chromosome 8.  This gene’s transformation can verify the diagnosis of CHARGE in those cases.  However, in less than half the cases, a mutated gene cannot be found. For more information about this disorder, check out:

Is there a cure?

To date, there is no cure for Coloboma. However, contact lenses can be worn to make the eye appear ‘normal’. Also, sunglasses are a must as Coloboma makes the eye extra sensitive to light, even causing pain due to the iris’s inability to contract.  For those who are visually impaired, more research needs to take place. If not for them, for those who aren’t yet born, that they may not have to deal with this rare birth defect. Interestingly, some dogs are affected with Coloboma. Hopefully, with continued research and societal awareness, a cure could be just around the corner.

Finding support

If you or someone you love suffers from Coloboma, help is available. Join this support group

Or contact these organisations for more information about vision impairment and eye health:

You should not use this information as a substitute for consultation with a physician. If you suspect your child has Coloboma, make an appointment with an eye care professional. If your child has been prescribed glasses or contact lenses, encourage him to wear them. Seeing is essential in the child’s ability to learn, in his mobility, and in his exploration of his environment.

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