I can see a persons face clearly, in good conditions, to a maximum of 6 feet, (2m)

THE CAUSE:  A genetic condition called 'Leber's Optic Atrophy' or 'Leber's Hereditary Optic Neuropathy' - LHON

This condition causes the mitochondria to be defective and kill the optic nerve cells.   My sight could remain as is, deteriorate very slowly or go overnight.

Mitochondria are the major power source for cells, and the cells of the optic nerve have extremely high energy demands.   Mitochondria have their own DNA which caries the information for the enzymes that produce the ATP, from glucose and oxygen in our blood, that our cells use for energy.

Mitochondrial DNA mutations can interfere with the production of ATP, reducing the available energy for the cells so that they effectively 'starve to death' despite the presence of sufficient oxygen and glucose.