Kabuki syndrome

Definition

Coloboma is a term that describes certain conditions of the eye (or its surrounding structures) where there is a partial absence of normal tissue in the eye at birth. Coloboma can affect one or both eyes. If the condition is present in both eyes, it can affect them in the same or different ways. Depending on which part of the eye is affected, there are several types of coloboma: 

• Eyelid coloboma: A portion of the upper or lower eyelid does not develop. 

• Lens coloboma: A part of the lens (the part of the eye that focuses light onto the retina) does not develop. 

• Macular coloboma: The macula is the central part of the retina responsible for detailed vision, color, and daylight. Macular coloboma prevents the macula from developing normally. 

• Optic nerve coloboma: In this type of coloboma, the optic nerve (the bundle of nerve fibers that transmits light signals to the brain) is hollowed out, causing a reduction in vision. 

• Uveal coloboma: The uvea is the middle layer of the eye. This type of coloboma can affect the iris (the colored part of the eye), giving it a characteristic appearance resembling a keyhole or cat’s eye. 

• Chorioretinal coloboma: In this type of coloboma, part of the retina (the light-sensitive tissue lining the back of the eye) does not develop. 

Symptoms

The symptoms of coloboma depend on its location. An iris coloboma is visibly noticeable, as it has the appearance of a keyhole or cat’s eye. An eyelid coloboma is also apparent. Individuals with a coloboma affecting the front of the eye typically do not experience vision loss due to the condition. Depending on its size, other types of coloboma may cause vision loss. A child with Kabuki syndrome who has a coloboma affecting the macula or optic nerve will have reduced vision. Children with a partial lack of retina will experience a "field defect," meaning they will have no vision in a specific area, such as the upper part of the visual field. A vision impairment caused by coloboma may not be evident at birth. 

Treatment

There is no cure for coloboma, and treatment depends on the specific type of condition. Individuals with an iris coloboma can use colored contact lenses to make the iris appear round. Surgery can also correct the appearance of the iris. For other types of coloboma, it is important to help patients adapt to their vision problems.