Accommodation
Accommodation, Close & Distant vision
Accommodation : As the distant object moves closer , the image moves behind the retina to keep the image sharply on the retina , the lens accommodates.
Close vision : ciliary muscles contract, lens ligaments (suspensory) relax, and lens becomes rounder (more convex).
Distant vision : ciliary muscles relax, lens ligaments (suspensory) contract, lens becomes less convex (concave).
With age, the lens hardens and is less able to accommodate . After age 55 , accommodation is no longer possible (presbyopia) requiring corrective lenses
Pupil constriction : During accommodation , the Iris also constricts to narrow the pupil , permitting increased depth of focus. For very close objects external eye muscles move the eyeball in word (converge) to keep sharp focus.
Convergence : The movement of each eyeball is controlled by six eye muscles that allow the eyes to follow a moving object.
At the end of this lesson, students should know about
1. mechanism of accommodation
2. Control of accommodation
3. near and distant vision
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- Chapters 11
- Department Physiology
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Dr. Faryal Mazhar
