This review article examined differences of MRI appearances that can help clinicians assess and manage these important neuro-ophthalmic disorders. It also examined the role of optic nerve MRI as a prognostic indicator in acute optic neuritis (ON). The major findings of this review are summarised as follows: 1) Unilateral vs. bilateral ON: Neuromyelitis optica (NMO) and myelin oligodendrocyte glycoprotein (MOG) have a wide range of reports that vary from no reported cases to over 80% of ON cases being bilateral. However, both NMO and MOG appear to have a higher incidence of bilateral ON when compared to multiple sclerosis (MS) or ‘idiopathic’ ON, with the highest incidence reported as 23%. 2) Morphological appearance of the optic nerve on MRI: Clinical or radiographic appearance of optic nerve swelling may be more severe in MOG ON than other types of ON, as noted in three of five studies reporting optic nerve swelling secondary to MOG ON. 3) Location and length of lesions: Chiasmal involvement was noted in a majority of NMO patients (60-75%) in three studies while a range from 11% to 48% was noted in other studies. In contrast, chiasmal involvement in MOG patients was less common, ranging from 5% to 17% in eight reports and up to 21-25% according to two studies. Chiasmal involvement was uncommon in MS patients with the majority of studies finding involvement ranging from 0% to 15% except for one study with 33% involvement. Optic tract involvement was uncommon in all groups with NMO being the most affected at 7-18%, with one study showing 42%, compared to MOG patients with 2-13% and 13% in two MS studies. NMO was more likely to be associated with longitudinally extensive optic nerve lesions (LEON), which in contrast, is uncommonly found in MS. Similarly, MOG patients characteristically have LEON (in the range of 23-88%) with three reports showing significantly longer segments of optic nerve involvement in MOG when compared to NMO. 4) MRI appearance as a prognostic indicator: Intercanalicular location and more extensive lesions were associated with poorer visual outcomes in two studies. One study found that NMO had the worst visual prognosis compared to MOG and MS, and that longer optic nerve lesions in NMO patients were the strongest predictor of poor final visual acuity.