Night myopia is a correctable cause of decreased visual acuity under conditions of decreased illumination. Even people with 20/20 vision may have this problem. Correction of the decreased visual acuity in darkness may be especially important in certain occupations. Night myopia is related to the way light is refracted onto the retina. Even the normal or slightly nearsighted eye may not be able to focus the indigo-violet wavelengths of light on the retina.