Glaucoma Case Studies
Pseudodoubling of the Optic Nerve

Patient history/presentation: A 27-year old Caucasian male presented for continued management of previously diagnosed open-angle glaucoma. Past ocular history was significant for two previous strabismus surgeries and a consecutive exotropia; past medical history was remarkable for asthma and GERD. Medications included Alphagan b.i.d. OU, Serevent, Singulair, and Prilosec.

Slit lamp examination was within normal limits; gon-ioscopy revealed angles open to the scleral spur, 360° OU.

Dilated fundus examination of the right eye showed a pink optic nerve with C/D 0.2 and normal macula. (An OCT scan of the macula was also normal.) A coloboma 1 disc in size could be seen about 1 disc diameter inferior to the nerve, with a vascular pattern bearing striking resemblance to the optic nerve. An OCT scan of the pseudonerve showed depression with dropout of retina and RPE, with an appearance similar to the true optic nerve. A Humphrey 24-2 visual field OD showed a superior arcuate defect and inferior nasal step. In essence, the patient had a chorioretinal coloboma of the right eye and, therefore, the rarely described "pseudoduplication of the optic nerve."

Fundus examination of the left eye showed significant parapapillary atrophy inferior to the nerve, an optic nerve pit inferotemporally, and optic nerve cupping inferiorly; the macula appeared normal. An OCT scan of the left optic nerve was consistent with a left optic nerve pit. A visual field of this eye showed an enlarged blind spot with decreased sensitivities extending from the blind spot to central fixation.

Left: Optic nerve pit, OS. Right: Pseudodoubling of the patient's optic nerve, OD.

Treatment: Because the visual field defects corresponded to the noted structural abnormalities rather than optic nerve cupping, the previous diagnosis of glaucoma was thought to be inaccurate. Alphagan was discontinued.

Discussion: Our patient had a chorioretinal coloboma with resulting visual field loss; this mimicked glaucomatous field loss, leading to a misdiagnosis of glaucoma.

Colobomas are dysplastic excavations of the optic disc that are caused by the failure of the choroidal fissure to close during embryonic development. They may be unilateral or bilateral, and are most commonly inferonasal. A coloboma may occupy the entire disc or involve only surrounding RPE and choroid. They may occur in isolation, in association with choroidal or iris defects, or in association with systemic abnormalities.

	OCT scan of the pseudonerve, OD.

Only a few cases of pseudodoubling or true doubling of the optic nerve appear in the literature. In 2000, Pesudoves and Weisinger examined an 84-year-old woman with pseudodoubling of the left optic disc and an optic pit in the right eye -- the same presentation as our patient. In 1998, Barboni et al. reported treating a 66-year-old woman with doubling of her right optic disc. A MEDLINE search for pseudodoubling or pseudoduplication of the optic nerve revealed only two cases.

Three reports describe what was believed to be true optic nerve doubling, although only one appears in the English literature. True doubling of the nerve could be distinguished from pseudodoubling by an MRI showing two optic nerves, OCT evidence of nerve fibers exiting the eye through both sites, or fluorescein angiography revealing late hyperfluorescence at both sites. Unfortunately, none of the reports of true doubling contained such convincing evidence. (As it turns out, our patient was the first to have documented OCT findings.) However, in 1969, Lamba reported finding a double left optic nerve with a separate vascular tree, and produced an orbital X-ray showing two distinct optic foramen.

OCT scan of a normal optic nerve (for comparison).

Other optic nerve conditions that can mimic glaucomatous nerve and/or visual field changes (besides colobomas and optic nerve pits) include tilted disc syndrome, optic nerve drusen, and morning glory syndrome.

Unfortunately, our patient was lost to follow-up, precluding the acquisition of higher resolution OCTs or other forms of imaging.

This case was submitted by Christina I. Pacio, M.D., chief resident in ophthalmology, and Joseph Ducharme, M.D., director of glaucoma, at Brown University/Rhode Island Hospital in Providence, R.I. Dr. Pacio will be entering her glaucoma fellowship at Wills Eye Hospital in July. If you'd like to comment on this case, e-mail Ophthalmology Management at ifftda@boucher1.com.