The breaks that cause retinal detachments in colobomatous eyes are often hidden within the lesion and difficult to find.To elucidate the pathoanatomy and possible pathomechanism of such detachments, histological sections of eight choroidal colobomas were reviewed.Sections of the margin showed central continuation of the inner neuroblastic layer (the intercalary membrane) and eversion and separation of the outer neuroblastic layer. The opposite direction of continuity of the neuroblastic layers created a schisis-like configuration between the intercalary membrane and the everted outer retina. The zone of duplication was a point of retinal adhesion, but also a locus minoris resistentiae due to vitreous attachments and variable glial support at the margin.The subset of coloboma-associated retinal detachments requires both a central break in the inner layer and a break in the outer layer at the margin of the coloboma. The inner layer break may be precipitated by retinovascular ischemia or scleral stretching; that in the outer layer may be caused by vitreous traction on the margin of the coloboma or extension of the formerly isolated detachment through the outer marginal zone of decreased glial support.