Pseudoduplication of the optic disc initially resembling a bifurcated optic nerve in a strabismus child: a case...

Pseudoduplication of the optic disc is a rare clinical condition that is characterized by a circumscribed, disc-like lesion with radiating vessels but only one normal optic nerve. We report a rare case that initially resembled a bifurcated optic nerve in a strabismus child.

A 6-year-old female child was initially referred to our hospital due to perceptual exotropia of 15 degrees with poor fixation of the left eye. The visual acuity of the left eye was 3/100 with a refraction of + 1.75/- 1.25 × 175. Fundus images of her left eye revealed a circumscribed and disc-like lesion located one disc diameter (DD) below the true optic disc that showed profound central cupping resembling a second optic disc with a vascular supply. B scan ultrasonography showed an optic nerve with a bifurcated weak-echo region, suggesting that two strands originated from the optic nerve. Optic coherence tomography (OCT) demonstrated a large crater-like depression of the lesion, indicating a colobomatous defect covered by a mysterious membranous structure, a disturbed nerve fibre layer and the absence of regular outer retinal layers. A perimetric examination revealed a relatively superior defect. Magnetic resonance imaging (MRI) revealed the left eye globe showed an abnormal morphology and that the optic nerve was abnormally shaped and shifted nasally in the left eye. Fundus fluorescein angiography (FFA) of the left eye revealed the absence of independent vascular vessels in the disc-like lesion. Hyperfluorescence with patchy fluorescence was evident in the inferotemporal area of the disc. Vascular loops surrounding the temporal region were evident in both eyes. Her right eye was normal except for the vascular loop. We proposed that this represented a case of pseudoduplication of the optic disc. The patient did not undergo any treatment, and her visual acuity remained stable during the follow-up period.

Our patient presented with a deep and ectatic coloboma below the optic disc that communicated with the true optic nerve and was originally thought to indicate a bifurcated optic nerve. This case suggests that atypical ectatic colobomas should be considered before diagnosing malformations related to the optic nerve in double optic disc cases.