Superior Segmental Optic Nerve Hypoplasia: A Case Report and Literature Review.

Superior segmental optic nerve hypoplasia (SSONH) is a rare congenital anomaly in which there is underdevelopment of the superior part of the optic nerve. This leads to a reduction in the total nerve fibres constituting the optic nerve and can result in inferior visual field loss. SSONH is classically associated with maternal type 1 diabetes mellitus. We report an atypical case of SSONH associated with maternal gestational diabetes but with no prior history of maternal type 1 diabetes. We comment on the associated retinal nerve fibre layer (RNFL) changes, and also the corresponding ganglion cell layer (GCL) changes, which have not previously been explored using modern optical coherence tomography (OCT) macular segmentation. We discuss previous case reports on SSONH and outline the associated conditions. This review highlights the importance of correct and prompt diagnosis of this rare condition to avoid unnecessary investigation and undue long-term follow-up.