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Peripapillary coloboma simulating double optic disc
  1. Department of Ophthalmology, Arrowe Park Hospital, Upton, Wirral, Merseyside, L49 5PE
  1. Mr G G Kamath.

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Editor,—Doubling of the optic disc is rare and can manifest as true or pseudo doubling. A 64 year old man was referred by his physician who noted “a clear area between each optic disc on both sides” during a routine check. Visual acuities and anterior segments were normal. Funduscopy revealed an appearance simulating double optic discs on each side. The right eye showed a 2 disc diameter (DD) sized pale excavation 1 DD below the optic disc inferotemporally (Fig 1A), with patchy pigmentation along the margins. The inferotemporal branches of retinal vessels dipped into the lesion before re-emerging. The left eye also revealed a similar but slightly larger (3 DD) lesion 1 DD below the optic disc, the two being connected by parallel retinal vessels (Fig 1B). These vessels bifurcated just above the inferior lesion before dipping into its excavation and emerging to supply the inferior retina. The retina surrounding these lesions was hypopigmented. On fluorescein angiography the inferior disc-like lesions were hypofluorescent in the early frames (Fig 1C) and on late frames the entire lesion showed scleral staining (Fig 1D). B-scan ultrasound revealed ectatic coloboma below the optic discs in both eyes (Fig 1E, F).

Figure 1

Fundus photographs of right (A) and left (B) eyes showing inferior pale lesions simulating double optic discs. Early (C) and late (D) frames of fluorescein angiogram of the left eye showing hypofluorescence and scleral staining respectively of inferior disc like lesion. B-scan ultrasound of right (E) and left (F) eyes showing ectatic coloboma inferior to the optic discs.

Duke-Elder1 describes duplication of the optic disc as a rare anomaly wherein two discs, each provided with retinal vessels are seen in an otherwise normal eye. Rare cases of true duplication of optic discs with separation of optic nerve into two or more strands have been reported, based either on incidental necropsy findings,2 3 demonstration of two optic foramina in the same orbit on x ray,4 or angioscotomas5 as indirect evidence of the existence of double optic nerves. Pseudo doubling of the optic discs caused by lesions such as optic disc coloboma, peripapillary chorioretinal coloboma, or inflammatory foci are more common.6-9 Our case had bilateral isolated ectatic peripapillary chorioretinal coloboma simulating double optic discs.