lensesglasses

Lenses and glasses are optical devices designed to improve vision by correcting refractive errors, protecting the eyes, and reducing glare. A pair of glasses consists of lenses mounted within a frame that rests in front of the eyes; the lenses themselves are the optical elements that bend light.

Spectacles were developed in Europe during the late 13th century, with early lenses ground from glass and held in place by frames. Through centuries, lens materials evolved from crown glass to plastics, enabling lighter, thinner designs. In the 17th–19th centuries, bifocals and other multi-vision lenses emerged, culminating in modern progressive designs and specialized specialty lenses.

Common lens types include single-vision lenses for one viewing distance, bifocals with two focal regions, trifocals with three, and progressive lenses that provide a gradual change in power. Occupational and sports lenses offer specialized geometry. Photochromic and tinted lenses adapt to light; coatings can add UV protection, anti-reflective properties, and scratch resistance.

Most modern lenses are made from plastic materials such as CR-39 or high-index polymers, though some high-end applications still use glass. Polycarbonate provides impact resistance. Aspheric designs reduce distortion. Coatings include anti-reflective, scratch-resistant, UV-blocking, and blue-light filtering, depending on goals.

A professional fitting uses a recent eye prescription, pupillary distance and frame size to position the optical centers correctly. Lenses are prescribed with power, axis for cylindrical corrections, and prism if needed. Eyewear is regulated in many regions as an assistive medical device requiring a valid prescription and proper prescription labeling.