Pathogenic Implications of Subretinal Gas Migration Through Pits andAtypical Colobomas of the Optic Nerve

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Abstract
Objective To describe subretinal migration of gas and silicone oil in a seriesof patients with congenital cavitary optic disc anomalies and to further clarifythe pathogenesis of the associated maculopathy. Methods Medical records of 4 female patients, aged 8 to 34 years, who developedsubretinal gas migration after vitreous surgery for macular detachment associatedwith cavitary optic disc anomalies were reviewed. A theoretical model wasused to calculate the pressure differential required to induce subretinalgas migration through an optic pit. Results The 4 patients had bilateral atypical optic nerve colobomas or a unilaterallarge optic pit. A definite defect in the tissue overlying the disc excavationcould be seen in one eye, and intraoperative drainage of subretinal fluidthrough the disc anomaly was possible in all cases. Subretinal migration ofgas or silicone oil was seen intraoperatively in one case and first appearedbetween 1 and 17 days postoperatively in the remaining cases. Theoreticalcalculations suggest that the pressure differential required for migrationof gas through a small defect in the roof of a cavitary disc lesion is withinthe range of expected fluctuations in cerebrospinal fluid pressure. Conclusions These observations provide clinical confirmation of a defect in tissueoverlying cavitary optic disc anomalies and imply interconnections betweenthe vitreous cavity, subarachnoid space, and subretinal space. We theorizethat intermittent pressure gradients resulting from normal variations in intracranialpressure play a critical role in the pathogenesis of retinopathy associatedwith cavitary disc anomalies.

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