These vision problems may begin in one eye or simultaneously in both eyes. If vision loss starts in one eye, the other eye is usually affected within several weeks or months. This is known as the ‘acute’ phase.
The rate of progression can vary from immediate to over two years, but most people are severely impaired by three or four months. Over time, vision in both eyes worsens with a severe loss of sharpness (visual acuity) and colour vision.
LHON mainly affects the central vision, which is required for detailed tasks such as reading, driving, and recognising faces. Peripheral vision generally remains intact so the affected individual can walk around independently.
Although central vision gradually improves in a small percentage of cases, for most people the vision loss is permanent and visual acuity rarely changes thereafter. Vision loss is typically the only symptom of LHON, however some other symptoms have been reported. In these affected individuals, the condition is known as ‘LHON Plus’ with symptoms similar to multiple sclerosis, such as muscle weakness and poor coordination.