Eyeglass

Eyeglasses are devices consisting of hard plastic or glass lenses mounted in a frame that holds them in front of a person's eyes, typically using a bridge over the nose and arms which rest over the ears.

History

Eyeglasses were invented in Italy around 1290. The first eyeglasses had convex lenses that could correct both hyperopia (farsightedness), and the presbyopia that commonly develops as a symptom of aging. It was not until 1604 that Johannes Kepler published the first correct explanation as to why convex and concave lenses could correct presbyopia and myopia.

Types of Eyeglasses

There are various types of eyeglasses available today, each designed for people with specific vision problems.

• Single Vision Eyeglasses: These are the most common type of prescription lens. They have a single optical prescription power over the entire lens, to correct for a particular type of vision problem.

• Bifocal Eyeglasses: These lenses have two different optical powers. The upper part is generally used for distance vision, while the lower part is used for near vision.

• Trifocal Eyeglasses: These lenses have three different optical powers. They are used for distance, intermediate, and near vision.

• Progressive Eyeglasses: These lenses provide a smooth transition from distance correction to near correction, eliminating segment lines and allowing clear vision at all distances, including intermediate.

See Also

• Contact lens
• Optometry
• Ophthalmology
• Presbyopia
• Myopia
• Hyperopia

References

Eyeglass Resources
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