Your vision depends on how light is focused in your eye. An eye has different parts to it, such as the cornea, lens, and iris. These parts work together to refract, or bend, and focus light rays. With normal vision, light is focused on the back of the eyeball. This area is called the retina. But in some cases, all or part of the eye is not the right shape. This causes light to focus in the wrong place. It makes vision blurry. Three common problems with focusing include hyperopia, myopia, and astigmatism.
Emmetropia or normal vision happens when light focuses on the retina.
Hyperopia or farsightedness occurs when light focuses behind the retina. Nearby objects look blurry.
Myopia or nearsightedness occurs when light focuses in front of the retina. Distant objects look blurry.
Astigmatism occurs when light focuses in more than one place. Both nearby and distant objects can look blurry.
With age, the lens becomes stiff. Stiffening of the lens makes it more difficult for the lens to accommodate, or change shape, to focus light. This leads to presbyopia, or trouble focusing on nearby objects.