ONA is diagnosed by extensive ophthalmological investigation which may include:
- Visual field testing: visual field defects in optic neuropathies can take several patterns including central, diffuse, arcuate, and altitudinal defects. The pattern of visual field defect is not specific to any etiology and almost any type of field defect can occur with any optic neuropathy. However, altitudinal defects are more common in ischemic optic neuropathies and central, or cecocentral defects frequently accompany toxic/nutritional and hereditary optic neuropathies.
- Electrophysiological testing: Visual evoked potential (VEP) are often abnormal in optic neuropathies. Although VEP is not necessary for the diagnosis of optic neuropathy, it can be useful in patients with early or sub-clinical optic neuropathy who may have normal pupillary responses and no discernible optic disc changes on clinical examination
- Optical coherence tomography: a relatively new technique that uses low coherence light to penetrate tissue and a camera to analyze the reflected image. By performing circular scans around the optic nerve head, the peripapillary nerve fiber layer can be analyzed. This has been useful in the follow-up of patients with optic neuritis, traumatic optic neuropathy, and Leber’s hereditary optic neuropathy
Symptoms of ONA often include tunnel vision (also known as scotoma), blurred vision, and loss of other visual fields. These defects are diagnosed on further investigation using the aforementioned techniques.