Unit 7: Gradual Loss of Vision
1: Cataract
Physiology
By altering the tension of the lens zonules the lens changes shape to provide varying refractive power.
This process of 'accommodation' means that the incoming light-rays are always brought to a focus on the macula, regardless of whether they come from an object that is near or far away.
Beyond the age of 40 accommodation becomes more difficult (presbyopia) so near objects are blurred.
Presbyopia is corrected by reading glasses.
Normal lens
Adapted from: Illustration of a Normal Eye, National Eye Institute, National Institutes of Health, used under CC BY 2.0 / All edges cropped.