This is a medical question of type : symptoms 
 What are the symptoms of Leber hereditary optic neuropathy ? 
 What are the signs and symptoms of Leber hereditary optic neuropathy? Blurring and clouding of vision are usually the first symptoms of this disorder. 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. Over time, vision in both eyes worsens, often leading to severe loss of sharpness (visual acuity) and color vision. This condition mainly affects central vision, which is needed for detailed tasks such as reading, driving, and recognizing faces. In rare cases, other symptoms may occur such as heart arrhythmias and neurologic abnormalities (e.g., postural tremor, peripheral neuropathy, nonspecific myopathy, movement disorders), and a multiple sclerosis-like disorder. However, a significant percentage of people with a mutation that causes Leber hereditary optic neuropathy do not develop any features of the disorder. Specifically, more than 50 percent of males with a mutation and more than 85 percent of females with a mutation never experience vision loss or related medical problems. Additional factors may determine whether a person develops the signs and symptoms of this disorder. Environmental factors such as smoking and alcohol use may be involved, although studies of these factors have produced conflicting results. Researchers are also investigating whether changes in additional genes, particularly genes on the X chromosome, contribute to the development of signs and symptoms. The Human Phenotype Ontology provides the following list of signs and symptoms for Leber hereditary optic neuropathy. If the information is available, the table below includes how often the symptom is seen in people with this condition. You can use the MedlinePlus Medical Dictionary to look up the definitions for these medical terms. Signs and Symptoms Approximate number of patients (when available) Optic neuropathy 33% Arrhythmia - Ataxia - Central retinal vessel vascular tortuosity - Centrocecal scotoma - Dystonia - Heterogeneous - Incomplete penetrance - Leber optic atrophy - Mitochondrial inheritance - Myopathy - Optic atrophy - Polyneuropathy - Postural tremor - Visual loss - The Human Phenotype Ontology (HPO) has collected information on how often a sign or symptom occurs in a condition. Much of this information comes from Orphanet, a European rare disease database. The frequency of a sign or symptom is usually listed as a rough estimate of the percentage of patients who have that feature. The frequency may also be listed as a fraction. The first number of the fraction is how many people had the symptom, and the second number is the total number of people who were examined in one study. For example, a frequency of 25/25 means that in a study of 25 people all patients were found to have that symptom. Because these frequencies are based on a specific study, the fractions may be different if another group of patients are examined. Sometimes, no information on frequency is available. In these cases, the sign or symptom may be rare or common.