BIOL 031 Lecture Notes - Lecture 20: Zonule Of Zinn, Ciliary Muscle, Far-Sightedness
17 Sep 2020
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Document Summary
Bending of a light wave when it enters a medium where its speed is different. Refractive ability remains constant because curvature never changes. Refractive ability can be adjusted by changing curvature as needed for near or far vision. Accommodation ability to adjust strength of lens. Depends on shape; regulated by ciliary muscle. Change is strength and shape of lens. Accomplished by action of ciliary muscle and suspensory ligaments (zonular fibers) Distance vision- light rays from distance objects are parallel, so do not need much refraction to focus properly (sympathetic ns) Close vision- light rays from closer objects diverges and need much refraction to focus properly (parasympathetic ns) Measured at 20 feet with snellen eye chart. Nearsighted (myopic) unable to see far things (eyeball is too long (lens)) Farsighted (hyperopic) unable to see things up close (eyeball is too short) Presbyopia stiffness of lens, decrease in accommodation, age (what parents have) cheater glasses, difficulty seeing things close up.
