Ĭoloboma of the eyelid has a different embryologic origin from a coloboma of the globe. The term ‘lens coloboma’ is therefore a misnomer because the tissue lost in this defect is of the zonules rather than the lens. There is a corresponding flattening of the equator of the lens due to a lack of tension on the lens capsule, which may lead to subsequent contraction and notching in that region. Ĭoloboma of the lens is due to defective or absent development of the zonules in any segment. Colobomas of the iris or ciliary body result from failures of complete anterior closure, while colobomas of the choroid, retina or optic nerve result rom failures of posterior closure. Defects in closure at either pole have different results. A large spectrum of disease can result from defects in closure ranging from mild and asymptomatic to microphthalmia or even anophthalmia. The process begins at the equator and proceeds anteriorly and posteriorly. Closure of the fissure begins on day 33 of gestation and allows for pressurization of the globe. Ĭlosure of the embryonic fissure occurs during the second month of embryonic development. In an ocular coloboma animal model in which retinol dehydrogenase is absent, supplementation with retinoic acid allows for normal ocular development. Vitamin A (retinol), which has previously been shown to be crucial for normal eye development, is also thought to be integral to this process. This gap allows the hyaloid artery to access the inner eye and is crucial for continued ocular development. The embryonic fissure develops from eccentric invagination of the optic vesicle leaving a gap inferonasally. Eye colobomas are located in the inferior nasal quadrant. Ĭoloboma of the iris, ciliary body, choroid, retina and/or optic nerve derive from failed or incomplete closure of the embryonic fissure (also known as choroidal or optic fissure) during development. Note the eccentric invagination of the optic vesicle which forms the embryonic fissure. In either case, they can affect one eye (unilateral) or both eyes (bilateral).įigure 1. It is important to differentiate colobomas involving the globe from those of the eyelids. It can affect one eye (unilateral) or both eyes (bilateral). It is typically located in the inferonasal quadrant of the involved structure and is often associated with microphthalmia. The term is used to describe ocular defects of the eyelids, iris, lens, ciliary body, zonules, choroid, retina or optic nerve. Coloboma is derived from the Greek koloboma, meaning mutilated, curtailed, or with defect.
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