A Clinical and Optical Coherence Tomography Study of the Margins of Choroidal Colobomas

Abstract

To describe the features at the margin of the choroidal colobomas as evaluated clinically and by optical coherence tomography (OCT). Prospective observational case series. Seventeen patients (30 eyes) that presented to the outpatient department of a tertiary care center. Clinical examination and OCT testing of the 30 eyes. Description of OCT features of the margin of the choroidal colobomas. Histologically, there is no normal choroid, retinal pigment epithelium, or retina overlying choroidal colobomas; rather, the overlying tissue is an extension of the retina called the intercalary membrane (ICM). In these patients, OCT showed that transition from normal retina to the ICM could be categorized as abrupt or gradual and also showed that the inner neurosensory retinal layers continued as the ICM, whereas the outer layers could not be traced beyond a point. In some cases with apparently attached retina, subclinical retinal detachments were identified along the margin of the coloboma. In cases with retinal detachment, OCT allowed for identification of the precise site of communication between the sub-ICM space and subretinal space at the locus minoris resistentiae. The margin of the choroidal coloboma, in some cases, showed the appearance of a hump owing to inward turning of the retinochoroidal layers with thickening of the layers at the margin. In small colobomas, OCT revealed the ICM thickness comparable to normal retina but showed structural alterations. Fundus lesions that were clinically labeled forme fruste of choroidal coloboma seemed to have normal retinal thickness and layering on OCT. In 1 patient, a temporal optic pit was associated with the forme fruste choroidal coloboma in 1 eye; the fellow eye had a typical choroidal coloboma. Optical coherence tomographic evaluation of the margins of choroidal colobomas helps in understanding the transition from retina to ICM, detects subclinical retinal detachments, and aids in identifying the site of communication between the sub-ICM space and the subretinal space in eyes with retinal detachment.