Non-nasal, atypical retinochoroidal coloboma in pediatric patients: Case series and review

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TL;DR

This case series reports two pediatric patients with atypically located, non-nasal retinochoroidal colobomas, a rare finding not originating from the embryonic fissure. One case involved a temporal coloboma with tractional membranes in a neonate, and the other an inferotemporal coloboma with retinal detachment in a 9-year-old. These cases highlight the need for continued documentation and research into the pathogenesis of atypical colobomas, which remain poorly understood.

Full summary

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**Background:** Ocular colobomas occur in 0.5–2.2 per 10,000 live births and are typically caused by defective closure of the embryonal fissure, resulting in inferonasal defects. Atypical colobomas involve areas of the fundus not originating from the embryonic cleft and are extremely rare. Only two prior case reports of non-nasal atypical colobomas exist in the literature. This case series reports two unique pediatric cases of non-nasal retinochoroidal colobomas, one associated with iris coloboma and hypoplastic lens and the other with retinal detachment (RD).

**Methods:** This is a retrospective case series of two pediatric patients evaluated at Bascom Palmer Eye Institute. Case 1: A 3-week-old female neonate with microphthalmos in the right eye underwent examination under anesthesia with multimodal imaging, including fluorescein angiography (FA), B-scan, and intraoperative optical coherence tomography angiography (OCTA). Genetic testing was performed using the Inherited Retinal Disorders Genetic Panel by Invitae. Case 2: A 9-year-old female with bilateral sensorineural hearing loss and left mild hydronephrosis presented with acute vision loss. Examination under anesthesia, fundus photography, and genetic testing (Inherited Retinal Disorders Genetic Panel and GJB2 gene sequencing) were conducted. Surgical intervention included scleral buckle, pars plana lensectomy, vitrectomy, and silicone oil tamponade.

**Key Results:** Case 1: The right eye showed microcornea (6 mm), temporal iris coloboma, hypoplastic lens, and a temporal chorioretinal coloboma affecting the macula with tractional membranes and inferior hemorrhage. Axial lengths were 12.9 mm (right) and 18.9 mm (left). FA revealed mild leakage at the coloboma edge and peripheral avascularity in both eyes. OCTA showed retinal and choroidal thinning with disorganization of all retinal layers and no foveal depression. Genetic testing identified variants of unknown significance in ABCA4 and HMCN1 genes. No surgical intervention was indicated. Case 2: The right eye had microcornea (9.5 mm), cataract, and an inferotemporal chorioretinal coloboma from 6:00 to 9:00 sparing the macula, with a macula-off rhegmatogenous RD from 4:00 to 12:00. A small retinal break was found intraoperatively. After initial surgery, the patient developed recurrent RD with proliferative vitreoretinopathy (PVR) and secondary glaucoma, requiring multiple procedures. At 8-year follow-up, visual acuity was hand motion, intraocular pressure was controlled, and the retina was attached under silicone oil. Genetic testing revealed no pathogenic variants. Systemic work-up (karyotype, CT temporal bones, ECG, echocardiogram) was unremarkable.

**Clinical Implications:** Atypical non-nasal colobomas are rare and their pathogenesis remains unclear. Leading theories include defective rotation of the fetal fissure, accessory embryonic fissures, poor differentiation of fetal structures, neural crest anomalies, or early intrauterine inflammation. RD occurs in 8–50% of coloboma patients, and management of coloboma-related RD often requires pars plana vitrectomy with silicone oil, though anatomical success rates vary (40–100%). These cases underscore the importance of thorough ophthalmic and systemic evaluation, including genetic testing, and highlight the need for continued research into the molecular and embryological mechanisms underlying atypical coloboma formation.