The average age for cataract extraction is 72. However, it occurs in patients even in their 20's. In all patients there is a lost of elasticity of the lens of the eye that starts about age 7 and goes to age 70 which makes it difficult to read without glasses after about age 40. Glaucoma is an increased pressure in the eye that causes damage to the cells of the eye and when untreated, leads to blindness. If and when detected, it is generally easily treated and controlled with eye drops.
Nearsightedness is when one has the ability to see close but objects in the distance are blurry.
Farsightedness isn't exactly the opposite although in the prescription for glasses it is opposite. Astigmatism is when the eye is off round. Instead of being a spherical front surface of the eye it is more curved in one direction than the other. Presbyopia is the normal decrease in ability to read without glasses generally after age 40. For the last 25 years we have used a plastic lens to replace the existing lens in the eye in patients with cataracts.