Adjustment, especially the process by which the eye adjusts itself to focus on near objects. At rest, the eye is focused for distant vision, when its lens is thin and flat. To make focusing on a nearer object possible, the ciliary muscle of the eye contracts, which reduces the pull on the outer rim of the lens, allowing it to become thicker and more convex.
With age, the lens loses its elasticity. This makes accommodation more and
more difficult and results in a form of longsightedness called presbyopia. acebutolol A beta-blocker drug used to treat hypertension, angina pectoris, and certain types of arrhythmia in which the heart beats too rapidly.
The process by which the refractive power of the lens of the EYE is increased by constriction of the ciliary muscle, producing an increased thickness and curvature of the lens. Rays of light from an object further than 6 metres away are parallel on reaching the eye. These rays are brought to a focus on the retina, mainly by the cornea. If the eye is now directed at an object
closer than 6 metres away, the rays of light from this near object will be diverging by the time they reach the eye. In order to focus these diverging beams of light, the refracting power of the lens must increase. In other words the lens must accommodate.
The lens loses its elasticity with age, and thus becomes less spherical when tension in the zonule relaxes. This results in an increased longsightedness (presbyopia) requiring reading glasses for correction. (See AGEING.)
n. adjustment of the shape of the lens to change the focus of the eye. When the ciliary muscle (see ciliary body) is relaxed, suspensory ligaments attached to the ciliary body and holding the lens in position are stretched, which causes the lens to be flattened. The eye is then able to focus on distant objects. To focus the eye on near objects the ciliary muscles contract and the tension in the ligaments is thus lowered, allowing the lens to become rounder. Adjustments in *convergence also contribute to accommodation.
(convergence reflex) a reflex that occurs when an individual focuses on a near object, in which the crystalline lens becomes more convex, the pupils constrict, and the eyes turn inwards.... accommodation reflex
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