Structure of the Retinal Margin and Presumed Mechanism of Retinal Detachment in Choroidal Coloboma

To describe the vitreoretinal structure at the margin of the choroidal coloboma in infants and older patients using swept-source (SS) OCT.Retrospective case series.Nineteen eyes of 16 patients with choroidal coloboma (7 males, 9 females; average age, 12.3 ± 7.1 years).The patients were classified into 2 groups: infants 1 year of age or younger (3 eyes) and older patients (16 eyes). Each finding on SS OCT was documented according to previously defined histopathologic findings.Description of the SS OCT features of choroidal colobomas.Swept-source OCT showed that the extracolobomatous retina centrally traversed the margin to continue as the marginal intercalary membrane (MICM), whereas the outer layers of the MICM were reversed at the point (point of reversal [POR]). The expected duplication was seen in all infant eyes, but in none of the older eyes whose outer layers of the MICM were ambiguous. However, at the boundary between the layered MICM and monolayered central intercalary membrane (CICM), the POR was detectable in all patients. Further SS OCT analysis showed that the MICM schisis and CICM schisis occurred simultaneously with vitreous traction. Retinal detachments (RDs) seen in 4 eyes were connected to the only MICM schisis, and a MICM break was identified in 1 eye. Swept-source OCT showed that retinal pigment epithelial hyperplasia adhered tightly to the retina and that the glial triangle was adhered tightly to the sclera, indicating barriers to the development of RD after MICM schisis.Swept-source OCT first visualized the POR in infant eyes and showed that the POR was identifiable despite the atrophic changes in the outer layer of the MICM in the older eyes. Based on the POR location, we confirmed that the intercalary membranes reported in previous OCT studies were clearly differentiated between the MICM and CICM. We also showed that the presence of MICM and CICM schisis resulted from vitreous traction at the coloboma margin and that MICM breaks induced RD only if the barrier that prevented the development of RD was broken.