“This happened when the deficiency causes damage to the nerve that leads to your eyes.
“The nervous signal that travels from the eye to the brain is disturbed due to this damage, leading to impaired vision.
“The condition is called optic neuropathy and treatment involving B12 supplementation usually reversed the impairment.”
With sufficient damage, however, the cable of nerve fibre will lose its capacity to regenerate, causing some patients to lose their sight permanently.