Acuity Clearness of vision. Standard is 20/20 which means the individual see at 20 feet what they should be at that distance. Accommodation Ability to change and control the focusing of the eye. Astigmatism Condition where vision is distorted because the front of the eye is not totally spherical, i.e. it is shaped more like a football than a soccer ball. Clear vision is restored by an appropriate lens. Binocular Using both eyes together Convergence Turning of the eyes inward to see closer Fusion Ability to perceive objects seen with the two eyes as a single object. Hyperopia Farsightedness. It is easier to see in the distance than close up. A small amount of far-sightedness is normal in children but may affect their comfort and concentration at close distances, i.e. reading and writing. Myopia Shortsightedness. It is easier to see close up than in the distance. Motilities Movement of the eyes following a moving target. Multifocal A lens with an upper area for seeing in the distance and a lower area with a different prescription for close work. Minus Lens (Concave) Changes the path of light so that the focus is farther way. Given to correct shortsightedness. Perception Interpreting the information received by the eyes. Plus Lens (Convex) Changes the path of light so that it focuses closer. Given to correct far-sightedness. Presbyopia Condition associated with normal aging, resulting in difficulty reading at close distances. Stereopsis Ability to see depth and judge distance. Vergence Turning of the eyes to see singly at a given distance.