Clinical measures of optic nerve function and structure
| Structure/ function | Investigational technique | Measurement | Change in optic neuritis affected eyes |
|---|---|---|---|
| Function | High-contrast visual acuity | High-contrast resolution | Worsens acutely and improves over time4 |
| Function | Low-contrast visual acuity | Low-contrast resolution | Worsens acutely and improves over time4 |
| Function | Colour vision | Blue-yellow and red-green defects discrimination | Abnormalities in colour discrimination that correlate with RNFL thickness29 |
| Function | ERG | Physiological integrity of cone and rod responses | No difference in full field ERG.75 Loss of OHNC of multifocal ERG17 |
| Function | VEP | Demyelination of the visual pathway | Latency delay that improves in a fraction of affected individuals over time22 |
| Structure | Fundus photography | Shows structure of inner surface of the eye (retina, optic disc, macula and fundus) | Optic disc pallor, atrophy |
| Structure | MRI | Optic nerve atrophy, tissue injury, blood-brain barrier breakdown | |
| Structure | DTI | Imaging of white matter damage and integrity of visual white matter tracts | Axonal and demyelinating injury to optic nerve and postgeniculate white matter33 76 |
| Structure | MTR | Myelination status and axonal content of the optic nerve | Demyelinating injury77 |
| Structure | SLP | Measure RNFL thickness | Shows a decrease in retardance in eyes with axonal injury associated with visual field loss78 |
| Structure | OCT | Measure RNFL thickness | RNFL thickness decreases with MS and decreases further with MS-related ON79; shows acute thickening due to edema25 |
| Function | mfERG | Measures the transformation of slow membrane conduction in unmyelinated ganglion cell axons to fast saltatory conduction in myelinated axons | |
| Function | ONHC of the mfERG | Transient effects of conduction block due to reversible demyelination | Loss of this response signifies loss of myelination at the lamina cribosa and disrupted transition from membrane to saltatory transmission17 |
| Function | mfVEP | Sensitive measure of axonal damage | Abnormal latency80 |
| Function | Pupillometry | Measurement of pupil diameter as an indicator of neural inhibitory mechanisms | Pupillary reflex metrics impaired81 |
DTI, diffusion tensor imaging; ERG, electroretinogram; mfERG, multifocal ERG; mfVEP, multifocal VEP; MS, multiple sclerosis; MTR, magnetisation transfer imaging ratios; OCT, optical coherence tomography; ONHC, optic nerve head component; RNFL, retinal nerve fibre layer; MTR, magnetisation transfer imaging ratios; SLP, scanning laster polarimetry; VEP, visual evoked potential.