The lens is found in the pupil of the eye. The focus distance of the eye is changed by modifying the shape of the lens. To put it another way, it focuses the light rays that travel through it (and onto the retina) to create crisp images of objects at varied distances. Refractive errors are a form of visual issue that makes seeing clearly difficult. They occur when the shape of your eye prevents light from properly focusing on your retina (a light-sensitive layer of tissue in the back of your eye). Refractive errors can be corrected with glasses or contact lenses, or surgery can be used to rectify the refractive fault. The most prevalent type of vision trouble is refractive errors. Over 150 million Americans have a refractive defect, but many are unaware that their vision could be improved.