A cleft eye, known medically as a coloboma, is a condition where a gap or hole exists in one of the structures of the eye. This defect is present from birth and results from the incomplete formation of the eye during early development in the womb. Colobomas can appear in one or both eyes and can affect various parts, from the colored iris to the internal structures at the back of the eye. The appearance and impact of a coloboma depend on which part of the eye is missing tissue, with effects on vision ranging from unnoticeable to significant.
The Developmental Origins of a Cleft Eye
The formation of a coloboma traces back to the second month of fetal development. During this period, the eye develops from a structure with a seam, called the optic fissure, that must fuse together. When this fissure fails to close completely, a gap remains, resulting in a coloboma. This process is sometimes compared to a zipper that doesn’t fasten all the way, leaving an opening.
This failure of the optic fissure to close often occurs sporadically, meaning it happens by chance without a clear cause. However, genetics can play a role, and mutations in specific genes like the PAX2 gene have been linked to colobomas. The condition can be inherited, but it does not guarantee a child will be born with it. Environmental factors during pregnancy, such as alcohol use, may also increase the risk.
Types and Visual Characteristics
One of the most common and visible types is an iris coloboma, which affects the colored part of the eye. This results in a pupil that is not perfectly round, often described as having a “keyhole” or “cat-eye” shape. An iris coloboma might primarily cause increased sensitivity to light because the pupil cannot contract properly to limit incoming light.
Colobomas can also occur in structures at the back of the eye, which are not visible without specialized instruments. A retinal or choroidal coloboma means a piece of the light-sensing layer (retina) or the underlying blood vessel layer (choroid) is missing. Because these layers are responsible for capturing images, a gap can create a blind spot in the field of vision. The size and location of this gap determine the severity of vision loss.
An optic nerve coloboma involves a defect in the nerve that connects the eye to the brain. The optic nerve may appear hollowed out, which can significantly impair vision. This type often leads to reduced visual acuity that cannot be fully corrected with glasses and may cause issues with depth perception or a reduction in peripheral vision.
Associated Health Conditions
While a coloboma can be an isolated condition affecting only the eye, it can also be a feature of a broader genetic syndrome that impacts multiple body systems. The presence of a coloboma may prompt physicians to look for other signs to determine if it is part of a larger diagnosis.
One notable condition associated with coloboma is CHARGE syndrome. This is a rare disorder, and the name is an acronym for several of its common features:
- Coloboma
- Heart defects
- Atresia of the choanae (blocked nasal passages)
- Retardation of growth and development
- Genital abnormalities
- Ear abnormalities
Other genetic conditions may also include coloboma. For example, Cat Eye Syndrome, a chromosomal disorder, is named for the vertical colobomas that can give the eyes a feline appearance. Kabuki syndrome and Treacher Collins syndrome are other genetic disorders where colobomas can occur alongside a range of other developmental differences, including distinct facial features and skeletal abnormalities.
Diagnosis and Management
A coloboma is often identified during a newborn’s first eye examination. If the coloboma affects the iris, its keyhole shape is often immediately apparent. For colobomas located deeper within the eye, a comprehensive dilated eye exam is necessary for diagnosis. While a coloboma may be detected on a prenatal ultrasound, a full assessment is performed after birth.
There is no treatment to replace the missing tissue or fill the gap created by a coloboma. Management focuses on maximizing existing vision and addressing any related symptoms or complications. This involves using glasses or contact lenses to correct refractive errors like nearsightedness or farsightedness. For an iris coloboma, special cosmetic or tinted contact lenses can be used to make the pupil appear rounder and reduce light sensitivity.
Long-term monitoring is important for individuals with certain types of colobomas. The structural differences in an eye with a retinal or optic nerve coloboma can increase the risk of developing other eye problems over time, such as glaucoma or retinal detachment. Regular check-ups with an eye specialist are recommended to catch these potential complications early and preserve vision.