Some people liken the eye to a camera. As light passes through the lens it is bent and transposed onto the eye’s film – the retina. The film is then ‘developed’ by the brain, becoming the image that we see.
As light enters the eye it first passes through the cornea – the clear ‘window’ to the eye. Because the cornea is curved, the light rays bend (refract). Light then passes through the pupil to the lens. The iris – the colored portion of the eye – controls the amount of light that enters the eye with muscles that cause the pupil to contract if there is too much light or to dilate if there is too little light. When light hits the curved surface of the lens it is refracted, or bent even more, so that it focuses properly on the retina. The retina then turns the light into electrical energy, which passes through the optic nerve to the brain stem, and into the occipital lobe where it is converted into an image. To summarize:
· Cornea – clear surface of the eye. Light rays refract as they pass through to the pupil.
· Iris – colored portion of the eye. The iris controls the amount of light that passes through the pupil.
· Pupil – an open space in the center of the iris. Light passes through the pupil to the lens.
· Lens – refracts light to focus it properly on the retina.
· Retina – converts light rays into electrical energy. This electrical energy is passed to the optic nerve.
· Optic Nerve – serves as a pathway to the brain stem, which forwards electrical energy to the occipital lobe.
· Occipital Lobe – electrical energy is converted into an image.
This process works perfectly in people with 20/20 vision. Imperfect vision occurs when the shape of the eye is irregular or when the light rays do not focus directly on the retina – these imperfections are collectively known as refractive errors.