PION is a rare cause of visual loss, patients mostly presenting with sudden onset of blurred vision, dyschromatopsia, pain and positive relative afferent defect (RAPD).
The diagnosis of PION is usually a diagnosis of exclusion, however, the emergence of modern neuroimaging technique with diffuse weighted image (DWI) and apparent diffusion coefficient (ADC) sequences in MRI provides more evidence for accurate diagnosis and management. MRI findings, in T2 DWI series, demonstrates a focal high hyperintensity signals at the optic nerve level, the area corresponding with the hypointensity area in the ADC series, which is a powerful clue to PION.
It is important to differentiate PION from inflammatory demyelinating optic neuritis (ON) because the prognosis is quite different, and appropriate interpretation of neuroimaging may aid in correct diagnosis of PION, hence providing adequate and accurate prognosis and treatment to patients.