Spectacles

Spectacles, also known as eyeglasses or glasses, are devices consisting of glass or hard plastic 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

The concept of spectacles has been around since the Roman Empire, but it wasn't until the 13th century in Italy that the first wearable glasses were invented. These early spectacles had convex lenses that could correct both hyperopia (farsightedness), and the presbyopia that commonly develops as a symptom of aging.

Design

Spectacles are designed to fit comfortably on the face while providing the necessary correction to the wearer's vision. The lenses are designed to correct refractive errors by bending light rays in a way that allows them to focus on the retina.

Types

There are various types of spectacles, including:

• Single vision spectacles - These have one uniform refractive index. They are used to correct conditions like myopia (nearsightedness), hyperopia, and astigmatism.
• Bifocal spectacles - These have two different refractive indices. They are used to correct presbyopia.
• Trifocal spectacles - These have three different refractive indices. They are used to correct near, intermediate, and far vision.
• Progressive spectacles - These have a gradient of refractive indices. They are used to correct near, intermediate, and far vision without the visible lines of bifocal or trifocal lenses.

See also

• Contact lens
• Optometry
• Ophthalmology
• Visual perception

References

Spectacles Resources
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