The eye functions like a camera. Light rays enter the eye through the cornea (the clear front window), pass through the pupil (the hole in the center of the iris), and then through the lens, finally reaching the retina (the film) at the back of the eye. When light rays land on the retina, they form an upside-down image.
The retina converts the image into impulses that travel through the optic nerve to the brain, which converts them into upright visual images.
Vision is clear only if the cornea and lens correctly bend or "refract" the light rays and focus them on the retina. Blurry vision may be due to what is called a "refractive error" --- the failure of the cornea and lens to focus light properly. Prescription eye glasses, contact lenses, and refractive surgery correct or improve Refractive Errors by focusing light rays closer to, or directly onto, the retina.
More than 90 percent of our knowledge is obtained through our eyes making vision the most valued of the five senses. However, millions of people suffer from diseases, disorders or injuries to the eye.