Uveal coloboma is a congenital eye condition characterized by a “hole” or “gap” in a part of the eye’s structure due to incomplete development during gestation. This can affect one or both eyes, with visual impact varying by size and location.
What is Uveal Coloboma?
The term “coloboma” originates from a Greek word meaning “curtailed.” Uveal coloboma is a defect in the uvea, the eye’s middle layer. This layer includes the iris (colored part, controls pupil size), the ciliary body (produces fluid, aids focusing), and the choroid (vascular layer, nourishes the retina).
Uveal coloboma forms from incomplete closure of the optic fissure, an embryonic structure present during fetal eye development. This fissure normally closes between the fifth and seventh weeks of gestation. If its margins fail to fuse, a gap remains, forming a coloboma. It is usually located in the lower-nasal quadrant of the affected eye, where the optic fissure develops.
The type of uveal coloboma depends on the affected uvea part. An iris coloboma results in a “keyhole” or “cat-eye” shaped pupil. If the choroid and retina are involved, it is a chorioretinal coloboma, where retinal tissue and its blood vessels are absent. Colobomas can also involve the optic nerve or lens.
Causes and Genetic Links
Uveal coloboma can arise sporadically or be inherited. The underlying cause is often linked to genetic mutations that disrupt eye development. Several genes have been identified in connection with coloboma formation, including PAX6, CHX10, SOX2, and SHH. Anomalies in these genes can lead to developmental defects.
When coloboma occurs as part of symptoms affecting multiple body systems, it is syndromic coloboma. Examples include CHARGE syndrome (Coloboma, Heart defect, Atresia choanae, Retarded growth and development, Genital hypoplasia, and Ear anomalies/deafness) and COACH syndrome (Cerebellar vermis hypoplasia, Oligophrenia, Ataxia, Coloboma, and Hepatic fibrosis). Specific gene mutations, such as CHD7 for CHARGE syndrome, are often responsible for these anomalies. Isolated coloboma affects only the eye, without other systemic issues.
While genetic factors are prominent, environmental influences during pregnancy may also contribute to coloboma development. Studies have explored connections to nutritional deficiencies like vitamin A deficiency. The majority of cases are attributed to genetic predispositions, with molecular genetic testing identifying a causative genetic defect in up to one-fifth of individuals.
Symptoms, Diagnosis, and Associated Conditions
Symptoms of uveal coloboma vary depending on the size and location of the missing tissue. If the coloboma affects the iris, a keyhole-shaped pupil may be noticeable. If the defect is internal, such as in the retina or optic nerve, it might not be immediately apparent. Visual symptoms can include reduced vision, sensitivity to light (photophobia), and uncontrolled eye movements (nystagmus). Some individuals may also experience blind spots or issues with depth perception.
Diagnosis of uveal coloboma occurs through a comprehensive eye examination, often performed shortly after birth or in early childhood. An ophthalmologist uses an ophthalmoscope to examine the internal structures of the eye for characteristic gaps or undeveloped tissue. Further assessments, such as visual field testing, may be conducted as the child grows to understand the impact on their vision.
Identifying uveal coloboma prompts screening for associated systemic conditions, especially if a syndrome is suspected. Syndromic coloboma can affect other organs beyond the eye, including the heart, kidneys, and brain. Coloboma can be linked to conditions like microphthalmia (abnormally small eyeballs) or anophthalmia (absence of an eyeball). A thorough review of systems and family history is conducted, and parents may also be examined for colobomas.
Management and Support
There is no “cure” for uveal coloboma, as missing tissue cannot be restored. Management focuses on optimizing vision and addressing complications. Corrective lenses help manage blurred vision or focusing issues. Low vision aids, including magnifiers and screen readers, assist individuals with significant vision impairment. For light sensitivity, tinted lenses or sunglasses provide comfort.
Surgical interventions manage complications rather than repairing the coloboma. Surgery may be necessary for conditions such as retinal detachment, cataracts, and glaucoma. Cosmetic surgery or colored contact lenses can improve the appearance of an iris coloboma.
Regular eye check-ups are important to monitor for potential complications like glaucoma or retinal detachment, allowing for early detection. For children, early intervention is important to prevent amblyopia, or “lazy eye.” Genetic counseling provides information for families regarding inheritance patterns and recurrence risks. Support networks and resources are also available to help individuals and families.