13.11  Coloboma Associated Retinal Detachment

Retinochoroidal colobomas are characterised by an absence of choroid, retinal pigment epithelium (RPE), and retina within the defect. An extension from the adjacent normal retina called the intercalary membrane (ICM) sits directly upon the ectatic sclera.[6] Subclinical RD has been reported along the margins of a coloboma. In these cases, optical coherence tomography (OCT) is essential pre-operatively for identifying the site of communication between the sub-ICM space and subretinal space. The zone of adhesion near the coloboma margin is known as the ‘Locus minoris resistentiae’ (LMR) or the point of least resistance.[6] Separation of the ICM from the sclera is termed ICM detachment. Peripheral retinal tears, ICM breaks, and dehiscence in the LMR can, in isolation or in combination, lead to RD. OCT imaging should be utilised to ensure there is no connection between the RD and the ICM detachment in colobomatous eyes with a peripheral retinal break and RD. Concurrent peripheral retinal breaks and LMR dehiscence allows the RD to extend into an ICM detachment. Conversely, breaks in the ICM accompanied by LMR dehiscence lead to RD. (Figure 13.11.1) illustrates these various scenarios.