Septo-optic dysplasia presenting with nystagmus, pseudo-disc edema, and fovea hypoplasia.

Background: Septo-optic dysplasia (SOD) is a condition that affects the early development of the brain and eyes. It presents with a combination of optic nerve hypoplasia, brain midline structure abnormalities, and pituitary gland hypoplasia.

Methods: This is a case report of a 4-year-old male who presented with low amplitude horizontal nystagmus and decreased visual acuity 20/60 OU. Further imaging and electrophysiology were conducted to classify the ocular presentation.

Results: No iris transillumination was noted, but foveal hypoplasia and disc edema were evident on fundus examination. This prompted neurology consultation and MRI imaging. The MRI was consistent with the diagnosis of SOD showing hypoplasia of the optic nerves, chiasm, and tracts and an absent septum pellucidum, but with normal pituitary development and function. Lumbar puncture and intracranial pressure were normal. Genetic testing identified one pathogenic variant in the SLC45A2, indicating carrier status for oculocutaneous albinism type 4 (OCA4). Flash Visual Evoked Potentials (VEPs) were consistent with chiasm dysfunction or hypoplasia rather than the chiasmal misrouting of OCA.

Conclusion: This case report further elaborates the phenotypic variation of SOD, with the finding of blurred disc margins, in the absence of the typical optic nerve double ring sign and with normal intracranial pressure. The findings of fovea hypoplasia and blond fundi lead to the suspicion of OCA either as a separate diagnosis with a second pathogenic variant in SCL45A2 not yet identified or in association with SOD. This case highlights the importance of electrophysiology to help distinguish chiasmal hypoplasia or dysfunction from OCA misrouting.