There may or may not be any symptoms related to coloboma; it all depends on the amount and location of the missing tissue. People with a coloboma affecting the macula and the optic nerve will likely have reduced vision. In general, it is difficult to exactly predict what level of vision a baby will have only by looking at how much of the retina is missing. A more precise estimate of the level of vision can be obtained over time, as the child grows and can perform more vision tests.

People with a coloboma affecting any part of the retina will have what is called a “field defect”. A field defect means that a person is missing vision in a specific location. Because coloboma is located in the lower part of the retina, vision in the upper part of the field of vision will be missing. This may or may not be noticeable to the affected person and may or may not affect performing daily activities.

A person with a coloboma affecting the front of the eye only will not have any decreased vision from it. Some people, however, have reported being more sensitive to light.

It is believed that uveal coloboma is primarily genetic in origin. “Genetic” means that the coloboma was caused by a gene that was not working properly when the eye was forming. Sometimes coloboma is part of a specific genetic syndrome, for which the genetics are known. For instance, coloboma is one feature of CHARGE syndrome, which is associated with a change in, or a complete deletion of a gene called CHD7 in most cases.

Researchers have found genes associated with an eye malformation in the microphthalmia, anophthalmia, coloboma (MAC) spectrum in up to 20% of cases. To date, however, we still do not know which genes explain most cases of coloboma.

Some researchers have proposed that certain environmental factors may contribute to developing coloboma, either in humans or in animals. These findings have been published over time in the research literature, but there has been no systematic analysis of possible links. For instance, it is known that babies exposed to alcohol during pregnancy can develop coloboma — but they also have other anomalies. There are no known strong links between environmental exposures and isolated coloboma.

It is always possible that coloboma happens strictly by chance. In summary, there is little data to presently say why coloboma happened to a person in a family where no one else is affected.

How does uveal coloboma happen?

To understand how uveal coloboma happens, we first have to understand how the eye forms in the developing baby. The eyes start as stalks coming out of the brain. The tip of each stalk will become the eye itself, while the rest of the stalk will become the optic nerve linking the eye to the brain. There is a seam at the bottom of each stalk, where blood vessels originally run. This seam is known as the optic fissure, or the choroidal fissure, or the embryonic fissure. Starting at the fifth week of gestation (pregnancy), this seam must close. The closure starts roughly in the middle of the developing eye and runs in both directions. This process is finished by the seventh week of gestation. If, for some reason, the closure does not happen, a uveal coloboma is formed.

Depending on where the closure did not happen, the baby can have an iris coloboma (front of the fissure), a chorio-retinal coloboma (back of the fissure), or any combination of these. Uveal coloboma can affect one eye (unilateral) or both eyes (bilateral). The condition can be the same in both eyes (symmetric) or different in both eyes (asymmetric). A uveal coloboma may go from front to back (continuous) or have “skip lesions”. The fact that the seam runs at the bottom of the stalk is the reason why uveal coloboma is always located in the lower inside corner of the eye.

How can uveal coloboma be inherited?

Isolated coloboma can follow all possible patterns of single gene inheritance, namely autosomal dominant, autosomal recessive and X-linked. In one family, however, coloboma will follow only one pattern. For instance, in case of an autosomal dominant pattern, a person with coloboma would have a one in two chance of passing on the coloboma to each of his or her offspring. In families with a single case of coloboma, it is not possible to say what pattern of inheritance is involved; therefore, it is not possible to give an exact recurrence risk number. The recurrence risk of coloboma computed from averaging data across many families (empiric risk) is about 10 percent. This is an imperfect number, as it mixes information from families where this risk may be close to 0 percent with information from families where the actual risk may be 25 percent or even 50 percent.

The topic of inheritance of coloboma is complicated by several factors:

• Sometimes a person who is at risk for developing coloboma may not develop the condition, or it may be so minor that it goes unnoticed. This may appear in the family history as an inconsistent, non-interpretable pattern of inheritance.
• Knowing the pattern of inheritance of coloboma in a family does not give information on how the vision of an at-risk person will be affected. The location (front vs. back of the eye), side (left eye, right eye or both) and size of the coloboma cannot be predicted.
• There may be more than one gene involved in being at risk for coloboma, and environmental factors might play a role.

For coloboma due to a known syndrome, such as CHARGE syndrome, inheritance is based on what is known about the genetic basis of that particular syndrome. However, it is rarely, if ever, possible to say whether coloboma will be a feature of the syndrome in a person inheriting the genetic background responsible for this syndrome.

There is no cure for retinochoroidal coloboma. Treatment varies depending on the conditions or complications that present in each individual. In some instances, retinochoroidal colobomas do not cause any symptoms and treatment is not necessary. Complications that commonly occur include:

• Tear or detachment of the retina (retinal detachment)
• Growth of new blood vessels beneath the retina that disrupt vision (choroidal neovascularization)
• Clouding of the lens (cataracts)
• Increased eye pressure leading to damage to the optic nerve (glaucoma)

Treatment of retinal detachment depends on the severity of the condition. For smaller retina tears, laser surgery (photocoagulation) or freezing treatment (cryopexy) may be utilized to induce a scar that helps to secure the retina to the eye wall. For larger tears or a detachment, surgery is typically needed to place the retina back into its proper position. Options may include: scleral buckle, pneumatic retinopexy, or vitrectomy. Surgical treatment of retinal detachment in individuals with retinochoroidal coloboma can be challenging and has variable success.

Treatment for choroidal neovascularization may include administration of medications that can block the abnormal growth of blood vessels (anti-VEGF treatment), thermal laser treatment to destroy abnormal blood vessels, and photodynamic therapy to damage unwanted blood vessels.

Cataracts are usually treated surgically via a technique called phacoemulsification. In this procedure, an instrument is used to break up and remove the cloudy lens. A lens implant is then placed to allow light to pass through and focus properly on the retina.

Glaucoma treatment varies and may include medication or surgery. Various surgical techniques can be utilized including: laser trabeculoplasty, laser iridotomy, peripheral iridectomy, trabeculectomy, and aqueous shunt surgery. The goal of surgery in glaucoma is to reduce the pressure on the eye.