See-Saw Nystagmus in a Patient with Septo-Optic Dysplasia

Abstract

Septo-optic dysplasia, also called de Morsier syndrome, is characterized by optic nerve hypoplasia, absence of the septum pellucidum, and thinning of the corpus callosum. Only once before has this rare form of nystagmus been reported in a patient with septo-optic dysplasia (1). We present such a case and document the findings with videography. A 37-year-old woman was referred because of bitemporal visual field defects detected on a routine examination. The patient had no pertinent past medical history. Physical examination revealed a woman of normal stature and weight. Best-corrected visual acuity was 20/20 in the right eye and 20/40 in the left eye. The anterior ocular segment was unremarkable. Pupils constricted normally to direct light without an afferent pupillary defect. See-saw nystagmus was present, manifesting intorsion of the elevating eye and extorsion of the depressing eye. (Video, Supplemental Digital Content 1, https://links.lww.com/WNO/A2). Ophthalmoscopy showed bilateral small tilted hypoplastic optic discs with a temporal crescent in the right eye. There was no double-ring sign (Fig. 1).FIG. 1: Fundus photography shows bilateral hypoplastic optic discs.Humphrey visual fields (30-2 protocol) showed bitemporal defects that had partial respect for the vertical meridian in both eyes with a central island of retained field in the right eye temporally (Fig. 2). Stratus III optical coherence tomography (OCT) showed decreased thickness of the retinal nerve fiber layer superiorly and inferiorly (Fig. 3).FIG. 2: Humphrey visual fields (protocol 30-2, gray scale) show bitemporal hemianopic defects consistent with optic chiasmal dysfunction.FIG. 3: Optical coherence tomography shows bilateral thinning of the retinal nerve fiber layer in both eyes, which is more marked nasally.Brain MRI showed absence of the septum pellucidum and reduced optic nerve and chiasmal thickness, findings consistent with de Morsier syndrome (Fig. 4).FIG. 4: Precontrast coronal brain MRI shows absence of the septum pellucidum (asterisk) and moderate thinning of the optic chiasm (arrow).Our patient with septo-optic dysplasia presented with see-saw nystagmus, which is characterized by elevation and intorsion of one eye with depression and extorsion of the other eye in one-half cycle, followed by reversal of those movements in the next half cycle. This type of nystagmus is believed to result from a defect that prevents the eyes from compensating for head rotations. Apart from this case of de Morsier syndrome, see-saw nystagmus is associated with isolated congenital absence or a decrease in the number of retinal ganglion cell axons crossing in the chiasm, parasellar masses, trauma to the optic chiasm, retinitis pigmentosa, rod cone dystrophy, midbrain lesions, and brain irradiation (3). Danielle S. Rudich, MD Mount Sinai School of Medicine Department of Ophthalmology New York, New York Robert L. Lesser, MD Departments of Ophthalmology and Visual Science and Neurology Yale University School of Medicine New Haven, Connecticut [email protected] Acknowledgment We thank Michael C. Brodsky, MD (Mayo Clinic Department of Ophthalmology, Rochester, MN) for his comments.