Eye Can See Clearly Now

Basic Anatomy The eye is approximately 2.54 cm wide, 2.54 cm deep and 2.3 cm tall.

Working from the outside in  Sclera – tough outermost layer of the eye that maintains the shape  Cornea – front sixth of the sclera which all light must go through

Next Layer (Choroid)  Front part of this layer contains two parts the ciliary body (muscles) - a muscular area that is attached to the lens. It contracts and relaxes to control the size of the lens for focusing. the iris - the colored part of the eye. The color of the iris is determined by the color of the connective tissue and pigment cells. Less pigment makes the eyes blue; more pigment makes the eyes brown. The iris is an adjustable diaphragm around an opening called the pupil. Iris has two muscles that make it larger (and thus the pupil smaller) or smaller (and thus the pupil larger) which allows less or more light in. Pupil size can change from 2 millimeters to 8 millimeters which could change the amount of light that enters by 30 times.

Innermost Layer  Retina – the light sensing part of the eye  Contains a chemical called rhodopsin, or "visual purple." This is the chemical that converts light into electrical impulses that the brain interprets as vision.  The retinal nerve fibers collect at the back of the eye and form the optic nerve, which conducts the electrical impulses to the brain.

 Two fluid-filled sections separated by the lens. The larger, back section contains a clear, gel-like material called vitreous humor. The smaller, front section contains a clear, watery material called aqueous humor.

How Do We See??!!?? 1. The light rays enter the eye through the cornea (transparent front portion of eye to focus the light rays) 2. Then, light rays move through the pupil, which is surrounded by Iris to keep out extra light 3. Then, light rays move through the crystalline lens (Clear lens to further focus the light rays ) 4. Then, light rays move through the vitreous humor (clear jelly like substance) 5. Then, light rays fall on the retina, which processes and converts incident light to neuron signals using special pigments in rod and cone cells. 6. These neuron signals are transmitted through the optic nerve, 7. Then, the neuron signals move through the visual pathway: Optic nerve → Optic Chiasm → Optic Tract → Optic Radiations → Cortex 8. Then, the neuron signals reach the occipital (visual) cortex and its radiations for the brain's processing. 9. The visual cortex interprets the signals as images and along with other parts of the brain, interpret the images to extract form, meaning, memory and context of the images.

Retina  Contains two types of cells Rods handle vision in low light Cones handle color vision and detail

Interesting Facts  Rhodopsin – decays upon light contact Part of the structure of the chemical requires Vitamin A – thus a deficiency in your diet causes vision problems Rebuilds itself but takes a few moments  This is why it takes time for your eyes to adjust to dim lights  Your eye focuses the image upside down on your retina but your brain interprets it correctly People who have their life “switched” (put glasses on them that make everything look upside down) will see things upside down for a while but after a day or so will begin to see things the correct way – the brain is magnificent in its capabilities

Normal Vision

Nearsightedness  Eye is too long or lens focuses too well. Image is in front of the retina Fixed with concave lens

Farsightedness  Eye is too short or lens doesn’t focus well enough Fixed with convex lens