Acoloboma (from the Greekκολόβωμα, meaning "defect")[1] is a hole in one of the structures of theeye, such as theiris,retina,choroid, oroptic disc. The hole is present from birth and can be caused when a gap called thechoroid fissure, which is present during early stages of prenatal development, fails to close up completely before a child is born. Ocular coloboma is relatively uncommon, affecting less than one in every 10,000 births.
The classical description in medical literature is of akeyhole-shaped defect. A coloboma can occur in one eye (unilateral) or both eyes (bilateral). Most cases of coloboma affect only the iris. The level of vision impairment of those with a coloboma can range from having no vision problems to being able to see only light or dark, depending on the position and extent of the coloboma (or colobomata if more than one is present).
Iris coloboma in the right eye of a 10-month-old child. The pupil cannot contract to a smaller size than pictured, but may still be able to dilate in low light.
Visual effects may be mild to more severe depending on the size and location of the coloboma. If, for example, only a small part of the iris is missing, the vision may be normal; when a large part of the retina or (especially)optic nerve is missing, the vision may be poor. Commonly posterior colobomata affect the inferior retina, with resultant deficit in the superior visual field. Other conditions can be associated with a coloboma. Sometimes, the eye may be reduced in size, a condition calledmicrophthalmia.Glaucoma,nystagmus,scotoma, orstrabismus may also occur.[citation needed]
Other ocular malformations that include coloboma or are related to it:
CHARGE syndrome, a term that came into use as anacronym for the set of unusual congenital features seen in a number of newborn children.[2] The letters stand for:coloboma of the eye,heart defects,atresia of the nasalchoanae,retardation of growth and/or development,genital and/or urinary abnormalities, andear abnormalities and deafness. Although these features are no longer used in making a diagnosis, the name has remained.
Cat eye syndrome, caused by the short arm (p) and a small section of the long arm (q) of humanchromosome 22 being present three (trisomic) or four times (tetrasomic) instead of the usual two times. The term "cat eye" was coined because of the particular appearance of the vertical colobomas in the eyes of some patients.[citation needed]
Treacher Collins syndrome, autosomal dominant syndrome caused by mutation ofTCOF1. Coloboma is part of a set of characteristicfacies that features craniofacial malformations, such as downslanting eyes, ear anomalies, or hypoplasia of zygomatic bone and jaw (micrognathia).[citation needed]
Tilted disc syndrome, an unusual congenital malformation associated withmyopicastigmatism characterized by tilting of the intraocular tip of the optic nerve (the optic disc), also known asFuchs coloboma.[citation needed]
Coloboma can be associated with a mutation in thePAX2 gene.[3] Eye abnormalities have been shown to occur in over 90% of children withfetal alcohol syndrome.[4]
Typically a coloboma appears oval- or comet-shaped with round end towards the centre. There may be a few vessels (retinal or choroidal) at the edges. The surface may have irregular depression.[citation needed]
Coloboma of the iris may be treated in a number of ways. A simple cosmetic solution is a specialized cosmetic contact lens with an artificial pupil aperture. Surgical repair of the iris defect is also possible. Surgeons can close the defect by stitching in some cases. Vision can be improved with glasses, contact lenses or even laser eye surgery but may be limited if the retina is affected or there isamblyopia.[5]
^Hornby, SJ; Adolph, S; Gilbert, CE; et al. (Mar 2000). "Visual acuity in children with coloboma: clinical features and a new phenotypic classification system".Ophthalmology.107 (3):511–20.doi:10.1016/S0161-6420(99)00140-2.PMID10711890.
