Optic Nerve Diastasis in a Patient With CongenitalOptic Nerve HypoplasiaAmit Gaur, MD, FRCS,a David Squirell, MRCOphth,a John P. Burke, FRCS,a andPaul D. Griffiths, PhD, FRCRb

Congenital optic nerve hypoplasia (ONH) is a relatively common,nonprogressive, developmental abnormality of the eye and has be-come recognized as a major cause of blindness in children.1 Al-though it may occur as an isolated event, a wide range of neurologicand endocrine abnormalities may be associated with ONH. Wepresent a case of congenital ONH in which optic nerve diastasis wasobserved on magnetic resonance imaging.

A 10-month-old boy presented with intermittent leftexotropia of 3 months’ duration. His visual acuitywas 6/12, with both eyes open as measured by

Cardiff cards (Keeler Ltd., Windsor, UK) at 1 m. A strongobjection to right eye occlusion was noted. Ocular exam-ination revealed poor fixation with the left eye, full ocularmovements, normal anterior segments, a comitant 50� leftexotropia, normal fundi, and no significant refractive er-ror. A diagnosis of left exotropia with possible amblyopiawas made. Right eye occlusion was advised, and the boywas monitored. A year later, when more accurate visiontesting with Kay Picture test (Kay Pictures, Tring, Herts,UK) was possible, the visual acuity in the his left eye wasnoted to be 1/60, whereas it was 6/6 in the right eye. A 10to 20� left exotropia was noted, and poor fixation with theleft eye and objection to occlusion of the right eye per-sisted. On fundus examination, the right eye was normal,whereas the left optic nerve was hypoplastic. Electrophysi-ologic testing revealed subnormal visual-evoked responsesto left-eye stimulation.

MRI of the brain and orbit confirmed that the left opticnerve was hypoplastic all the way back to the optic chiasm(Figure 1 A). No evidence was found of any other intra-cranial abnormalities, such as the absence of the corpuscallosum or a mass lesion relating to the optic apparatus.High-resolution T2-weighted images showed that a shortsegment (approximately 4 mm) of the left optic nerve wasdiastatic within the optic canal. The optic sheath wasdeformed in the vicinity of the diastasis as shown in Figure1B. At the last follow-up visit in January 2004, visual acuity

Author affiliations: aDepartment of Ophthalmology, bAcademic Unit of Radiology, RoyalHallamshire Hospital, Sheffield, United Kingdom

Submitted February 28, 2005.Revision accepted April 26, 2006.Reprint requests: Dr. A. Gaur, MD, FRCS, 15 Coed Y Wenallt, Cardiff, UK,

CF14 6TN (email: amitgaur@doctors.org.uk).J AAPOS 2006;10:482-483.

Copyright © 2006 by the American Association for Pediatric Ophthalmology andStrabismus.

1091-8531/2006/$35.00 � 0doi:10.1016/j.jaapos.2006.04.006

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in the patient’s left eye was 1/60, with persistent inabilityto take up fixation and an exotropia of 15�.

DiscussionMRI confirmed the diagnosis of ONH in our case de-scribed here. This method is reliable to confirm opticnerve and chiasmatic hypoplasia.2 It is important for theophthalmologist to recognize that ONH may be associ-ated with extended pathology in the central nervous sys-

FIG 1. Coronal high-resolution T2-weighted images through the opticnerve. The more anterior image (A) shows left ONH. Note that on thissequence cerebrospinal fluid has a high signal (white) and the nerve itselfis low signal ( black). More posteriorly (B) the nerve is split into two, andthe optic sheath is deformed from its usual rounded configuration,resembling a heart shape, lying on its side.

tem. An important clinical association of ONH with mid-

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line cerebral defects, such as absence of the septum pelluci-dum, agenesis of the corpus callosum, dysplasia of theanterior third ventricle, and hypopituitarism, is referred to assepto-optic dysplasia.3 With the advent of high-resolutionneuroimaging, it is now appreciated that ONH may be as-sociated with a wider spectrum of central nervous systemmalformations. Structural central nervous system abnormal-ities on computed axial tomography brain scans were de-scribed in 90% of cases with ONH in a series that includedagenesis of the corpus callosum, porencephaly, diffuse cere-bral and cerebellar atrophy, cystic paraventricular leukoma-lacia, suprasellar arachnoid cyst, schizencephaly, aqueductstenosis, hydrocephalus, and holoprosencephaly.4 MRI hasbeen shown to be a more sensitive modality for detectingintracranial abnormalities in patients with ONH.5 Reportsusing magnetic resonance imaging in ONH have shownposterior pituitary ectopia, infundibular hypoplasia, and ce-rebral hemispheric abnormalities, which included schizen-cephaly, cortical heterotropia, posterior fossa arachnoid cyst,periventricular leucomalacia, and diffuse encephalomala-cia.5-8

The left ONH in our case was associated with opticnerve diastasis. Optic nerve splitting has been describedafter trauma and penetration by an aneurysm.9,10 Ourreview of literature* revealed no previous report of con-genital optic nerve diastasis or its association with ONH.

*A search was conducted on PubMed using the terms optic nerve,hypoplasia, intracranial abnormalities, anomalies, congenital, splitting,

diastasis, dehiscence, MRI, and computed tomographic scans.

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