The human eye functions like a camera. Light enters through the cornea, passes through the pupil, and is focused by the lens onto the retina, which contains photoreceptors that convert light into electrical signals sent to the brain.

One common refractive defect is myopia (nearsightedness), where distant objects appear blurred because the eye is too long or the lens is too curved, causing light to focus in front of the retina. The corrective measure is wearing concave lenses, which diverge light rays, allowing them to focus properly on the retina, improving distance vision.