Because there is a clear pattern of LHON genetic inheritance, those with a family member on the maternal inheritance bloodline with a LHON mutation should expect that any sudden, painless central vision loss they experience is likely caused by LHON. However, carrying the LHON mutation does not mean that a LHON carrier will lose central vision; most who carry a LHON mutation do not.Approximately 50% of men carrying an LHON genetic inheritance will lose vision in their lifetime; whereas only about 10% of women carriers will be affected.

Those who are not aware of any family members with LHON are taken by surprise when they suddenly lose central vision. Since LHON is so rare, the medical community usually suspects, tests and treats for other causes of sudden vision loss. An MRI may be conducted to rule out a brain tumour.

Since vision loss usually begins in just one eye, the tentative diagnosis of optic neuritis is often made and a three or five day steroid treatment is often prescribed. When vision doesn’t improve and the second eye also begins losing vision, there may be more tests such as a VER (Visual Evoked Response) and a Lumbar Puncture (aka Spinal Tap) to rule out other possible causes of sudden vision loss.

A specific test of the blood or saliva can usually determine if someone carries a LHON mutation.  Some labs test for just the three most common LHON mutations.  Others test for 20 LHON mutations, which include many of the very rare mutations.

A list of labs that conduct LHON testing can be found at: GeneTests

GeneDx offers a LHON test which includes 20 LHON mutations.  They offer a variety of programs designed to ensure that their LHON genetic testing is affordable to all.

​Genetic testing can be ordered by a physician or a genetic counsellor.  Genetic counselling with a LHON expert is available by phone at: