Accommodation – Focusing apparatus of the eye

Accommodation is the mechanism by which the focusing apparatus of the eye adjusts to objects at different distances. The effect is to bring divergent rays, those coming from an object nearer than 20 feet, into focus on the retina. (When the distance from a light source to the eye is greater than 20 feet, the divergence of rays is so slight that for practical purposes they may be assumed to be parallel.) In the normal eye, parallel rays of light are brought to an exact focus on the retina without the need for accommodation.

Rays coming from a near object (divergent rays), however, are focused behind the retina. Distant objects therefore appear distinct and near objects blurred. If the refractive power of the eye is increased through accommodation, parallel rays will be brought to a focus in front of the retina, while divergent rays will be focused on the retina. Near objects will therefore appear distinct, and distant objects blurred.

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