Mother Nature's Pop Science Guide to The Human Eye - Part One

Mother Nature's Pop Science Guide to THE HUMAN PART ONE Two eyes on the front of the face focus on an item from The major function of the eyebrows is to keep forehead perspiration from falling into the eyes. 1 out of every 5 people has pupils of different diameter, which can actually change size independently and alter their balance in a few hours. Those with blue eyes possess larger ones, on average, than brown-eyed people. separate angles. This enables 3-D vision by producing a slightly đifferent background on each retina. COMPOSITION OF THE EYE With direct contact to air, we must keep our trans- parent corneas moist since they have no blood vessels to provide them with oxygen. The tear glands and eyelids are evolution's answer, as each blink is a little dunk in the primeval sea. EYEBROW IRIS We blink 14,000 times a day, or about 23 minutes in 24 hours. The average blink lasts a third of a second. EYELID The whites of the eyes highlight eye movements by sharply contrasting with the darker iris and pupil. TEAR DUCT The visible eye is about one-sixth of the entire ball, and its fascinating effect stems from its three interacting parts: white, iris and pupil. CONJUNCTIVA OF THE EYEBALL PUPIL EYELASHES Vision is the eye's ability to form an image of an object and send that image to the brain's visual centers – similar to how a camera works. Light rays from the object pass through the eyeball and finally reach the retina. Behind the retina, the optic nerve connects to the brain, delivering the image. HOW THE EYE SEES RETINA BRAIN SCLERA CORNEA IRIS OPTIC NERVE VITREOUS HUMOR LENS The test for sharpness of vision is usually given with a standard chart that consists of rows of letters. The letters in each line gradually shrink as one reads down. From a distance of 20 feet, the patient reads aloud the letters that he or she can recognize. 20/20 vision is seen as normal. The metric system uses a distance of 6 meters and normal vision is expressed as 6/6. VISION ACUITY 20/200 20/100 тOZ 20/70 L PE D PEC F D 20/50 20/40 EDF C Z P 20/30 FELOPZ D 20/25 DEFPOTEC 20/20 D, E, F, P O... LEFOD PCT FDPLT CEO 10 11 Eye care professionals and others use Snellen Chart to measure visual acuity. Defects in the shape of the eye include nearsightedness (myopia), farsightedness (hyperopia) and astigmatism. Farsightedness results when the eyeball is too short and the focus falls behind the retina. Nearsightedness is caused by the eyeball being too long and the focus falling in front of the retina. Astigmatism occurs from abnormalities in the shape of the cornea or the lens. VISION DEFECTS Concave lens NEARSIGHTEDNESS (Myopia) Convex lens FARSIGHTEDNESS (Hyperopia) Cylindrical lens ASTIGMATISM Color blindness is the inability to see red, green, blue or a mix of these colors. Most color-blind people can see only two basic colors of the spectrum, and they confuse other colors. More than 4 of every 100 men are color-blind, compared to about 1 of every 200 women. Color blindness is inherited and is present at birth. COLOR BLINDNESS NO COLOR VISION DEFICIENCIES DEUTERANOPIA PROTANOPIA TRITANOPIA If you have no color vision deficiencies, you will be able to see the number. Sources: Daniel McNeill's "The Face" / "World Book Encyclopedia" / "Compton's Encyclopedia" / http://www.buzzle.com/articles/eye-color-percentages.html / http://www.webmd.com/balance/features/why-we-cry-the-truth-about-tearing-up / http://www.colour-blindness.com/general/how-it-works-science / http://science.howstuffworks.com/life/human-biology/colorblindness2.htm / NTC's Dictionary of Everyday American English Expressions Infographic & Design: Chris Rooney mnn (@looneyrooneycom)/MNN