Definitions:
| Aqueous humor - the clear, watery fluid inside the eye. It provides nutrients to the eye. Astigmatism - a condition in which the lens is warped, causing images not to focus properly on the retina. Binocular vision - the coordinated use of two eyes which gives the ability to see the world in three dimensions - 3D. Cones - cells the in the retina that sense color. People have three types of cones, L cones that sense long wavelengths (reds, yellows), M cones that sense medium wavelengths (greens), and S cones that sense medium wavelengths (violets, blues). Cornea - the clear, dome-shaped tissue covering the front of the eye. Eyebrow - a patch of dense hair located above the eye. Eyelash - one of the many hairs on the edge of the eyelids. Eyelid - the flap of skin that can cover and protect the eye. Farsighted - (also called hyperopia) a condition in which distant objects are seen more clearly than nearby objects because light is focused behind the retina, not on it. Iris - the colored part of the eye - it controls the amount of light that enters the eye by changing the size of the pupil. Lens - a crystalline structure located just behind the iris - it focuses light onto the retina. Nearsighted - (also called myopia) a condition in which nearby objects are seen more clearly than distant objects because light is focused in front of the the retina, not on it. Optic nerve - (also called cranial nerve II) the nerve that transmits electrical impulses from the retina to the brain. Pupil - the opening in the center of the iris- it changes size as the amount of light changes (the more light, the smaller the hole). Retina - light-sensitive tissue that lines the back of the eye. It contains millions of photoreceptors (rods and cones) that convert light rays into electrical impulses that are relayed to the brain via the optic nerve. Rods - cells the in the retina that sense brightness (they are photoreceptors). Night vision involves mostly rods (not cones). There are many more rods than cones. Tear - clear, salty liquid that is produced by glands in the eyes. Vitreous - a thick, transparent liquid that fills the center of the eye - it is mostly water and gives the eye its form and shape (also called the vitreous humor). 20/20 Vision - normal human vision, a condition in which a person can see a letter of a specific size from a distance of 20 feet. |