Lhon, the abbreviation of Leber's hereditary optic neuropathy, is passed down from the mother to the offspring through the mitochondria. Mitochondria are eukaryotic cell organelles that are the powerhouses of the cell because they produce energy. Leber's hereditary optic neuropathy causes degeneration of retinal ganglion cells and subsequently the loss of central vision.Because it is a mitochondrially inherited diseases, it is not transmitted from father to offspring, only the egg from the mother contributes mitochondria to the embryo. Mutations of the mitochondrial genome are responsible for lhon and lhon is most common in young males.
Theodore Leber, a German ophthalmologist, first described lhon in 1871. He noted four families in which almost all the young men suffered from a suddenly loss of vision in one or both eyes. Wallace, in 1988, discovered the responsible mutations, three of which caused most of the cases of Leber's hereditary optic neuropathy. Some people who have this mutation never experience loss of vision and a woman who is a carrier of this mutation has 40% chances of giving birth to a son with lhon and 10% chances of an affected daughter. Environmental factors like smoking and alcohol intake play a role in the development of Leber's hereditary optic neuropathy.
The sequence of affect of Leber's hereditary optic neuropathy on eyes is as follows. First there is unilateral acute loss of vision and and slowly and gradually after weeks or months the other eye is also affected and its vision is lost. The nature of vision loss is central and the age of onset is that of a young adult. Females have a slightly higher age of onset of Leber's hereditary optic neuropathy. The is damage and atrophy of the optic nerve and an irreversible and non-curable visual acuity. It is very rare for only one eye to be affected and both eyes become affected simultaneously or soon one after the other. In the acute phase, that period of time for which is few weeks, there is oedema in the eye affected with Leber's hereditary optic neuropathy. Lhon also causes microangiopathy in the affected eye and this can be seen when a medical professional or an opthalmologist examines the fundus with the aid of a fundoscope. Pupillary defects may also be present and visible. Visual field examination reveals loss of color vision, cecocentral scotoma and loss of visual acuity.
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When it comes to diagnosis and management of lhon, Leber's hereditary optic neuropathy, family history is the most important factor without which it is difficult to establish a diagnosis. However, in the absence of familiar lhon, blood testing for mitochondrial DNA assessment and a neuro-ophthalmologic evaluation is done. Genetic counselling is offered and those at risk should be informed about the risk factors like the use if tobacco and alcohol which are optic nerve toxins. Early onset vision loss can be partially and successfully reversed bu a vitamin E metabolite, alpha tocotrienol quinone. Other than this, regular corrected visual acuity along with perimetry checks should be done as follow-up of the individuals affected with lhon.