Most people will probably own at least one pair of spectacles during their lifetime—prescription glasses to aid vision, sunglasses to cut down glare or simply to follow fashion, or goggles to protect the eyes from harmful particles. Many eye disorders can be corrected by wearing spectacles. Two commonly occurring problems are short sight and long sight. A person with short sight, or myopia, cannot see object at a distance clearly. This is because the light that enters the eye focuses in front of, rather than on the retina. Lenses prescribed for myopia place the point of focus further back so that it falls on the retina. In long sight or hypermetropia, right rays are brought to a point of focus behind the retina so that it is difficult to focus on near objects. Unlike short-sighted people, those with long sight can subconsciously correct the point of focus, but this produced eye strain and can result in headache and fatigue.

The right glasses will make the necessary adjustments. Astigmatism, which result in blurred areas of vision, is usually caused by a misshapen cornea—the front surface of the eye. This condition is often associated with other problems, and one pair of lenses will usually be sufficient. The lens inside the eye change shape to focus the eye for near vision. To do this the lens has a certain amount of elasticity. But as a person grows older the elasticity of the membrane may decrease and near vision becomes progressively blurred. This condition, known as presbyopia, usually appears around middle age and many people are prescribed reading glasses to correct it.