Choroidal Coloboma

In their OCT study of colobomas, Drs Gopal et al observed that the inner layers of the retina were continuous with the intercalary membrane, whereas the outer layers stopped abruptly or thinned out progressively.1Gopal L. Khan B. Jain S. et al.A clinical and optical coherence tomography study of the margins of choroidal colobomas.Ophthalmology. 2007; 114: 571-580Abstract Full Text Full Text PDF PubMed Scopus (38) Google Scholar The reason for not finding a schisislike reversal of the outer retinal layers as described previously2Schubert H.D. Schisis-like rhegmatogenous retinal detachment associated with choroidal colobomas.Graefes Arch Clin Exp Ophthalmol. 1995; 223: 74-79Crossref Scopus (24) Google Scholar may be related to the age of the patients examined. Their ages were collectively given as 9 to 49 years (mean, 19.5). The structure of the margin in an adult coloboma differs from that of the young in that it frequently features pigment epithelial hyperplasia and choroidal and scleral thickening in a compact intertwined arrangement (i.e., it can stop abruptly). Schisislike reversal and duplication of the outer retinal layers are less frequently found in adults, even though they might have been present when these individuals were young.3Schubert H.D. Structural organization of choroidal colobomas of young and adult patients and mechanism of retinal detachment.Trans Am Ophthalmol Soc. 2005; 103: 457-472PubMed Google Scholar Malformations age if allowed to do so, and they may change with time or have more compact features to begin with in adult survivors. The hump effect at the margin found on OCT may correspond to a scleral ridge first described by Hannover in 1888 as funiculus sclerae and by Mannhardt in 1897 as protuberantia sclerae foetalis. A ridge was found in almost one fourth of histological cases,3Schubert H.D. Structural organization of choroidal colobomas of young and adult patients and mechanism of retinal detachment.Trans Am Ophthalmol Soc. 2005; 103: 457-472PubMed Google Scholar yet its role at the margin remains to be defined, particularly with respect to risk of retinal detachment (RD). The OCT findings presented by Gopal et al give new life to ancient histological descriptions but, more importantly, demonstrate the locus minoris resistenciae at the margin that causes RD. Finding and treating the break using OCT and laser may prevent RD in a subset of colobomas.