Eyeglasses

Eyeglasses are wearable optical devices with lenses mounted in a frame. They correct refractive errors, protect the eyes, or provide specialized visual functions.

Refraction: Refraction is the change in a wave’s direction and speed as it passes between materials. Eyeglass lenses redirect light so it focuses appropriately on the retina.
Myopia: Myopia is a refractive error in which distant objects appear blurred because images focus in front of the retina. Diverging lenses in eyeglasses shift the focus of distant light backward.
Reading glasses: Reading glasses are lenses designed to improve near vision, commonly by adding positive optical power. They provide a simple near-focus aid, often for presbyopia.
Reading stone: A reading stone is a magnifying optical aid, often a convex piece of glass placed over text. It is an early precursor to wearable magnifying lenses.
Contact lens: A contact lens is a thin optical device worn directly on the eye’s surface. It corrects vision without a frame and sits closer to the eye than eyeglasses.
Diopter: A diopter is a unit of optical power equal to one reciprocal meter of focal length. Eyeglass prescriptions use diopters to specify lens power.
Hyperopia: Hyperopia is a refractive error in which images tend to focus behind the retina. Converging eyeglass lenses help bring the image onto the retina.
Bifocals: Bifocals are eyeglasses with two distinct lens powers for distance and near vision. Their separate optical zones address both far and close viewing.
Salvino D'Armate: Salvino D'Armate is a figure traditionally credited with inventing eyeglasses in late thirteenth-century Italy. His attribution illustrates the uncertain origins of the first spectacles.
Refractive surgery: Refractive surgery is an operation that changes the eye’s focusing power to reduce dependence on corrective lenses. It alters the eye itself rather than placing corrective optics in front of it.

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