A coloboma is a congenital malformation in which parts of the eye or the eyelid are not fully formed. The disorder arises during embryonic development when the tissue folds from which the eye is formed do not close completely. Depending on which structure is affected, a coloboma can look different and have different effects on vision.
Colobomas arise in the first weeks of pregnancy when the so-called optic fissure (fissura optica) does not close completely. This can have various reasons:
Since colobomas can be accompanied by other malformations (for example of the heart, the kidneys, the ears, or the airways), a comprehensive evaluation and, if necessary, genetic counseling are advisable.
In an iris coloboma, a piece of the iris is missing. The pupil then has a keyhole or teardrop shape. Vision can be normal, but those affected are often sensitive to light because the pupil cannot fully constrict. Cosmetic contact lenses can conceal the abnormality.
Parts of the suspension apparatus of the lens (zonular fibers) are missing, so that the lens has an unusual shape. This can result in a refractive error that must be corrected with glasses. Sometimes occlusion therapy (patch treatment) is also necessary to prevent amblyopia.
In this form, parts of the retina or the optic nerve are affected. The effects on vision can be considerable, especially when the central visual center (macula) is involved. These eyes are often smaller than normal (microphthalmos) and have an increased risk of:
Regular eye check-ups are particularly important for retinal and optic nerve colobomas.
An eyelid coloboma presents as a missing part of the eyelid: from a small notch to almost complete absence. It occurs most frequently on the upper eyelid and can occur as part of syndromes such as Goldenhar or Treacher Collins. The exposed cornea is endangered by the missing eyelid cover: drying out, infections, and scarring can result.
The therapy depends on the type and severity of the coloboma:
The visual prognosis depends strongly on which structures are affected. Iris colobomas usually hardly impair vision, whereas retinal or optic nerve colobomas can lead to a significant visual impairment. Close ophthalmological care and the early treatment of accompanying problems such as refractive errors or amblyopia are crucial to support the best possible visual development.