A common cause of low visual acuity is refractive error (ametropia), errors in how the light is refracted in the eyeball, and errors in how the retinal image is interpreted by the brain. The latter is the primary cause for low vision in people with albinism. Causes of refractive errors include aberrations in the shape of the eyeball or the cornea, and reduced flexibility of the lens. Too high or too low refraction (in relation to the length of the eyeball) is, respectively, the cause of near-sightedness (myopia) or far-sightedness (hyperopia); normal refractive status is referred to as emmetropia. Other optical causes are astigmatism or more complex corneal irregularities. These anomalies can mostly be corrected by optical means (such as eyeglasses, contact lenses, refractive surgery, etc.).