We found that (a) patients with AQP4-IgG seropositive NMOSD present with more impaired HCVA than MOGAD and MS despite similar retinal neuroaxonal damage; (b) in contrast, LCVA and MD are similarly affected in NMOSD, MOGAD and MS; (c) in all diseases the structure–function association followed a broken-stick model: there was no association between visual function and OCT above a certain threshold, but once a certain threshold was reached, more profound structural damage was associated with worse visual function. The gene discussed is AQP4; the disease is Menkes disease.