- A congenital malformation (birth defect) in which part of the eye does not form due to failure of fusion of an embryonic feature called the intraocular fissure. The resultant coloboma can be likened to a missing slice from a pie that may involve a number of different structures within the eye including the choroid, iris, lens, optic nerve, and retina. A coloboma can occur as an isolated defect in an otherwise normal baby, or it can be part of a multiple congenital malformation syndrome such as the cat-eye syndrome (named after the coloboma which gives the eye something of a feline look). Colobomas are also seen in the aniridia-Wilms tumor association (the concurrence of undergrowth of the iris of the eye and Wilms tumor of the kidney); and the trisomy 13 syndrome (a disastrous disease due to an extra chromosome number 13).
* * *Any defect, congenital, pathologic, or artificial, especially of the eye due to incomplete closure of the optic fissure. [G. koloboma, lit., the part taken away in mutilation, fr. koloboo, to dock, mutilate]- c. of choroid a congenital defect of the choroid and retinal pigment epithelium exposing the sclera; the defect is usually situated below the optic disk in the region of the fetal (choroid) fissure.- Fuchs c. a congenital inferior crescent on the choroid at the edge of the optic disk; not associated with myopia. SYN: congenital conus.- c. iridis 1. retention of the choroid fissure causing a congenital cleft of the iris, often associated with c. of the choroid; 2. obsolete term for the iris defect resulting from a large surgical iridectomy.- c. lentis a segment of the lens equator devoid of zonular fibers, giving the appearance of a notch.- c. lobuli congenital fissure of the lobule of the ear.- macular c. a defect of the central retina as a result of arrested development or intrauterine retinal inflammation.- c. of optic nerve a congenital notch in the formation of the optic nerve, appearing as a craterlike excavation at the optic disk. See optic pit.- c. palpebrale a congenital notch in the eyelid margin.- c. of vitreous a congenital indentation of the vitreous body by mesenchyme; associated with severe myopia.
* * *col·o·bo·ma .käl-ə-'bō-mə n, pl -mas also -ma·ta -mət-ə a fissure of the eye usu. of congenital origincol·o·bo·ma·tous -mət-əs adj
* * *n.a defect in the development of the eye causing abnormalities ranging in severity from a notch in the lower part of the iris, making the pupil pear-shaped, to defects behind the iris in the fundus. The enlarged pupil causes dazzle symptoms. A coloboma of the eyelid is a congenital notch in the lid margin.
* * *col·o·bo·ma (kol″o-boґmə) pl. colobomas, coloboґmata [L., from Gr. kolobōma defect, from koloboun to mutilate] 1. an absence or defect of tissue. 2. particularly, a defect of ocular tissue, usually due to malclosure of the fetal intraocular fissure, or sometimes from trauma or disease. Such anomalies range from a small pit in the optic disk to extensive defects in the iris, ciliary body, choroid, retina, or optic disk. A scotoma is usually present, corresponding to the area of the coloboma.
Medical dictionary. 2011.