Myopia
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(nearsightedness), happens when light from a distant object focuses in front of the retina.
Hyperopia
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(farsightedness), happens when light from a distant object focuses behind the retina.
Astigmatism
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happens when a point of light from an object doesn't focus into a point image, but instead, forms two line foci and a blurred zone between. It's like the distortion one sees in a "fun-house" mirror.
Presbyopia is the "eyes-over-forty" condition caused by the lens of the eye losing its elasticity with age.
Glacoma
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Glaucoma is a disease of the optic nerve, characterized by slow, progressive damage of the nerve over time, and, in many cases, elevated intra-ocular pressure.
There are many risk factors for glaucoma, chief among them are age, family history, ethnicity, pressure inside the eye, and corneal thickness.
Glaucoma is generally treated with eye drops, although some recalcitrant forms require surgery.
Cataracts
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Cataracts can develop from many causes, but aging in the primary risk factor.
They are caused by the cummulative effects over one's lifetime from exposure to ultra-violet rays from the sun.
Some types, however, are caused by certain medications, or by trauma or by radiation, and even others are congenital. Cataracts are removed surgically by an ophthalmologist and modern surgical results are amazingly good.
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