Back
Home
3.3 identify accommodation as the focusing on objects at different distances, describe its achievement through the change in strength of the lens and explain its importance
identify accommodation as the focusing of objects at different distances, describe its achievement through the change in strength of the lens and explain its importance
- Light rays reflected from an object six metres or more away are almost parallel to each other. The lens refracts these rays so that they fall on the fovea, the part of the retina where vision is sharpest. If an object is closer than six metres the light rays reflected from it will be diverging rather than parallel. To bend these light rays so that they fall on the fovea the lens must become more rounded.
- Accommodation is the ability of the lens to change shape and focus light from objects at a range of distances. If the lens becomes more rounded (greater curvature) it refracts light to a greater extent and close objects can be focused. If the lens becomes less rounded (less curvature) it refracts light less and distant objects can be focused.
- The ciliary muscles are responsible for adjusting the shape of the lens. When they relax, the lens is less rounded. When they contract, the lens becomes more rounded.
- Accommodation is important because it allows the eye to form focused images on the retina from objects at a range of distances from the eye.
Accommodation
- As a person ages the lens gradually loses its elasticity and can no longer accommodate for viewing close objects. Corrective spectacles are required.