13.11  Coloboma Associated Retinal Detachment

Retinochoroidal coloboma occurs secondary to a failure of closure of the optic fissure during weeks 5-7 of fetal development. Colobomas occur in 2–14 per 100,000 live births[1] of which 50% present unilaterally.[2] Causative genetic variants are found in 8% of cases[3] and whilst most are sporadic, autosomal dominant, recessive and X-linked inheritance patterns are reported. Colobomas occurring as a result of chromosomal defects are usually associated with systemic abnormalities. Perinatal environmental triggers include nutritional (maternal vitamin A, E and folate deficiency, hypothyroidism), drug exposure (mycophenolate, anti-convulsants, thalidomide), and maternal infections (CMV, toxoplasmosis, Zika virus).[4]

Retinochoroidal coloboma is a complex disorder with a variable prognosis requiring regular ophthalmic examination to monitor for sight-threatening complications including retinal detachment (RD). RD risk in patients with coloboma increases with age, with rates ranging from 2.4-47.5% in adult populations.[5]

Selzer EB, Blain D, Hufnagel RB, Lupo PJ, Mitchell LE, Brooks BP. Review of evidence for environmental causes of uveal coloboma. Surv Ophthalmol 2022;67(4):1031-1047.

Hussain RM, Abbey AM, Shah AR. et al. Chorioretinal coloboma complications: retinal detachment and choroidal neovascular membrane. J Ophthalmic Vis Res. 2017; 12: 3-10

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.

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