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How do eyes adjust to different distances?

Laura C. Fine, MD
Ophthalmology
Just behind the pupil (the black hole in the center of your eye) and iris (the colored part of your eye), lies the crystalline lens, which is connected at its outer rim to the ciliary body by ligaments called zonules. The lens focuses light rays on the retina, the thin, light-sensitive inner layer at the rear of the eye. Muscles in the ciliary body enable the flexible lens to alter its shape and allow the eye to focus on objects at varying distances. When you look at a tree far away, for instance, the muscles relax and stretch the zonule ligaments, which in turn pull on the lens, causing it to flatten and assume a thin contour. But shift your gaze to something close, such as a computer screen, and the muscles contract and loosen the zonules, which makes the lens thicker and curved more in the middle. The ability of the lens to focus from far to near is called accommodation.

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