Bilateral aplasia of the optic nerve, chiasm, and tracts in an otherwise healthy infant

Optic nerve aplasia is a rare developmental anomaly characterised by the congenital absence of the optic nerve, central retinal vessels and retinal ganglion cells that is seen most often in a unilaterally malformed eye.¹,² Unilateral optic nerve aplasia is generally associated with otherwise normal brain development while bilateral optic nerve aplasia is usually accompanied by severe and widespread congenital central nervous system (CNS) malformations.¹,² We report here a unique presentation of a unilateral microphthalmos associated with bilateral optic nerve, chiasm, and tract aplasia without any CNS or systemic abnormalities.

Case report

An 11 month old girl was referred to the neuro‐ophthalmology clinic because of unequal size of the eyes. She was born to non‐consanguineous parents at 39 weeks gestation with a birth weight of 2750 g. The neonatal period was unremarkable. Developmental condition other than ocular findings was normal. She was the first child of her parents and there was no history of significant ocular disease in her family. Her parents' ocular examinations were normal.

Physical examination was normal, the patient's weight, length, and head circumference were normal for her age. Neurological examination was normal except for vision.

On examination she had no behavioural response to bright light and the pupils were not reactive to it. Right corneal diameter was 10 mm and left 7.5 mm. Both corneas were clear and anterior chambers were formed. Iris hypoplasia was found in both eyes. There was a congenital cataract in the left eye but the lens was clear in the right eye. On dilated fundus examination, the right eye showed absence of optic nerve and central retinal vessels (fig 1). Numerous large, rounds to oval, circumscribed, whitish to yellow areas of retinochoroidal depigmentation were visible in the periphery (fig 1).

Figure 1 Fundus photograph of the right eye shows absence of optic disc, optic vasculature, and areas of retinochoroidal depigmentation.

B‐scan echography showed a small left globe (axial length 14.80 mm), normal size right globe (axial length 22.30 mm), and absence of optic nerve on both eyes.

Magnetic resonance imaging (MRI) of the orbits and brain disclosed marked asymmetry of globe size and bilateral absence of the optic nerve, chiasm and tract (fig 2A–D). There was only a rudimentary optic nerve behind both globes.

Figure 2 (A) T1 weighted axial MRI demonstrates right normal size globe with a rudimentary optic nerve and left microphthalmic eye. (B) Axial MRI of chiasmal section shows absence of chiasm. (C) T1 weighted axial MRI of optic tract section shows absence of tract signals. (D) T1 weighted sagittal MRI shows absence of optic chiasm.

TORCH titres were negative and genetic evaluation including DNA analysis was unremarkable. Serum level of growth hormone, TSH, thyroxin, and glucose were all within normal limits.

Comment

Optic nerve aplasia denotes complete absence of the optic nerve and disc, retinal ganglion and nerve fibre layer, and optic nerve vessels. Histopathological examination usually demonstrates a vestigial dural sheath entering the sclera in its normal position, as well as retinal dysplasia with rosette formation.¹,² The pathogenesis of optic nerve aplasia remains speculative. It may be due to defective formation of the embryonal fissure, failure of the mesenchymal anlage of the hyaloid system to enter the embryonal fissure, or primary agenesis of the retinal ganglion cells.³

Bilateral optic nerve aplasia is rare, with most reported cases having major CNS malformations.¹,²,⁴,⁵ To our knowledge there is only one previous report of bilateral optic nerve aplasia in an otherwise normal infant.⁶

Microphthalmos of the affected eye was a consistent finding in previous reports of unilateral or bilateral optic nerve aplasia,¹,²,³,⁵,⁶,⁷ which was found only on our patient's left eye. To the best of our knowledge, this is the first case with bilateral optic nerve, chiasm, and tracts aplasia in an otherwise healthy infant with one microphthalmic and one normal size eye.