By the end of this, you should know: All the parts of the eye How vision works What causes color blindness What causes near- and far-sightedness
Vision Needs to be Developed An infant’s eyes are sensitive to light, but there are many visual skills that must be learned in the first year of life. What have you noticed when you have watched a baby looking at things?
How many directions can you move your eyes in? Eye Movement Each of your eyeballs is about an inch in diameter. Your eyes are surrounded by protective tissue. The muscles around your eyes are capable of some of the fastest movements in your body. How many directions can you move your eyes in?
Layers of the Eye The round walls of your eyes have three layers The sclera The retina A middle layer that provides a rich blood supply Sclera Retina
Cornea Light enters the eye through the cornea, a clear “window” in the sclera The cornea can heal itself very fast, in just a day or two, even though it has no blood supply. Cornea
How is the iris like the shutter of a camera? Pupil and Iris The amount of light entering the eye is monitored by the iris. The iris is made of involuntary muscles that adjust the size of the pupil based on how much light is coming in. Pupil Iris How is the iris like the shutter of a camera?
The Lens The lens focuses light entering the eye on the retina. The lens and the structures anterior to it are bathed a nutrient-rich fluid called aqueous humor. Lens
Photoreceptors Posterior area of eye The retina contains photoreceptor cells called rods and cones. Rods see dim light, gray tones, and motion. There are three types of cones, each sensitive to a different range of color. Rod Cone Interneuron
Photoreceptors Rods and cones adjust to changing light conditions In a dark room, your rods take over your vision. When you come back into the light, things look very bright because your rods need to adjust to the new level of light.
Fovea: The Blind Spot We have photoreceptors over our entire retina except in our blind spot The blind spot is where the optic nerve leaves the eyeball, carrying signals to the occipital lobe. Photoreceptors send signals to the brain through the optic nerve. Blind spot Optic nerve
Focusing Images When light passes through the lens, it is bent by the lens and focused on the retina. The exact point of focus is just beyond where all the incoming lines meet and cross. Because the light rays cross, the image they make on your retina is upside down.
Vision Problems In nearsighted eyes, the point of focus falls in a spot in front of the retina For farsighted people, the problem is the opposite― the focus is past the retina.
Vision Problems Eyeglasses can adjust how the light is bent when it enters your eyes. Lenses of different shapes will bend the light to different degrees so the point of focus falls on the retina.