Updated June 08, 2015.

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Leber's hereditary optic neuropathy (LHON) is a condition that causes sudden but painless central vision loss. LHON usually begins at a young age and affects males more than females. Vision loss can start in one eye but within six months it usually affects both eyes. Unfortunately, reduced central vision is often permanent. When LHON begins, the retinal nerve fiber layer that extends from the optic nerve becomes swollen.

Tiny, curvy blood vessels may appear around the optic nerve. Atrophy of the nerve tissue may also occur, causing vision loss.

Causes of LHON

LHON is an inherited disorder caused by a mutation in the the genes. The mutation occurs in the mitochondrial DNA and is inherited from the mother. Mitochondria are found in the cells and function to produce energy for cells. Scientist believe there are other factors in our environment that may play a role in the development of the disease. Although it is not definitive, it is thought that exposure to some antibiotics such as minocycline or erythromycin or other external factors that put stress on our mitochondria may cause the disease to express itself in those with the mutated gene.

Vision Loss and LHON

Vision loss occurs in the central vision, the vision used when looking directly at a target. The vision loss occurs suddenly in one eye, with the other eye being affected within 2-6 six months. Vision can progress from 20/20 to 20/200 or worse. Onset is usually in young adulthood, but has been known to occur in older people as well.

The average age of onset is between 15-30 years of age in men and between 20-40 years in women. Often a loss of color vision and a blind spot in the center of vision occurs.

Visual Recovery and LHON

For most people, vision loss is permanent. However, some people spontaneously recover some central vision a year after the first onset, and sometimes many years later. LHON is caused by mutated genes, and within those genes are subtypes of mutations. The chance of regaining vision lost by the disease depends on the particular mutation involved. For example, one mutation called 14484 has a 37-71% chance of some visual improvement. Another mutation, known as 11778, has only a 4% chance of visual recovery. It has also been discovered that LHON beginning before 10 years of age tends to have a greater vision recovery chance. Scientists have also discovered that people with a thicker nerve fiber layer and larger optic disc diameter seem to have slightly better visual recovery.

Inheritance of LHON

The gene for LHON is given by the mother. Affected females have non-affected fathers. Males will not pass the gene to any of their children, but females with the mutation will pass it to all of their children, regardless of whether they are sons or daughters.

Treatment of LHON

Treatment research for LHON is ongoing. Most physicians believe in first avoiding potential optic nerve toxins such as tobacco and alcohol use. Exposure to chemicals such as ethambutol has been linked to triggering LHON related vision loss. Some physicians also use a cocktail of supplements and vitamins to promote optic nerve health. Gene therapy is being investigated for treatment of LHON and holds the most promise. Because a time proven treatment has not been developed, physicians and other health care workers aim to train patients with central vision loss to use low vision aids, such as special microscopes and magnifiers to improve their visual function. Patients are also taught to use their intact peripheral vision to improve visual function and especially mobility.

What You Should Know

The genetic mutation responsible for LHON can also cause problems in cardiac muscle which can cause a higher incidence of heart conduction defects. Therefore, people that develop LHON should also see a heart specialist, in addition to a neuro-ophthalmologist.
_Sources:

1. Alexander, Larry. Treatment of Leber Hereditary Optic Neuropathy, Brain. Sept 2011.
2. Primary Care of the Posterior Segment, Third Edition. Appleton & Lange, 2002.