Incidental bilateral optic nerve hypoplasia.

Harvey JP. BMJ Case Rep 2017. doi:10.1136/bcr-2017-220343 Description A 19-year-old man was incidentally noted to have a bitemporal heteronymous hemianopia on automated perimetry during his first optician’s sight test (figure 1). The patient reported life-long reduced vision in the right eye although this was his first presentation to ophthalmic services. The patient was induced at 34 weeks due to poorly controlled gestational diabetes in his mother. The patient had no other ocular, medical, drug or family history. On examination, visual acuity was 6/9 in the right eye and 6/6 in the left eye. The anterior segment was normal. Funduscopy demonstrated bilateral hypoplastic optic discs with the characteristic ‘double-ring sign’ (figure 2). The disc diameter to disc–macula distance ratios were 0.33 and 0.31 in the right and left eyes, respectively (figure 3). There was no relative afferent pupillary defect, Ishihara testing was normal and there was no impairment of extraocular muscle function. All blood tests including pituitary function tests were normal. MRI of the brain, orbits and pituitary showed bilaterally thin optic nerves but no other abnormality (figure 4). Electrodiagnostic tests were normal. The patient was discharged from follow-up after his field defect remained stable at 2 years after presentation. Optic nerve hypoplasia (ONH) is a congenital abnormality of the optic nerve with an incidence of 10.9/100 000 per year. The pathophysiology of ONH is unknown; however, its aetiology has been linked to several maternal risk factors making an accurate gestational history extremely important. Associations that are relevant in this case report include young maternal age, primiparity, maternal smoking and gestational diabetes. Additional associations include maternal use of alcohol, recreational drugs, anti-depressants, anti-convulsants and anti-emetics. The classical clinical finding in ONH is of small optic nerve heads with a characteristic ‘doublering sign’. This finding appears as a pale white/ yellow ring around the optic disc, which is thought to represent the scleral canal. The ratio of disc diameter to disc–macula distance (measured from the temporal edge of the disc to the central fovea) Incidental bilateral optic nerve hypoplasia