eyeglasses

Eyeglasses, or spectacles, are devices with lenses mounted in a frame that rests on the nose and ears to correct vision. They address refractive errors such as myopia (nearsightedness), hyperopia (farsightedness), astigmatism, and presbyopia, and may also protect the eyes in certain environments. Lenses are typically made from glass or plastic, and modern versions may include coatings such as anti-reflective, scratch-resistant, ultraviolet protection, and blue-light filtering. Common lens materials include CR-39 plastic, polycarbonate, and high-index plastics.

Frames come in a range of materials, including metal, plastic, and composite, and in styles such as full rim, semi-rimless, and rimless. Prescription eyeglasses are prescribed after an eye examination by an optometrist or ophthalmologist, which determines the required refractive correction and often measures pupillary distance to ensure proper lens alignment. Lenses vary in type: single-vision lenses correct for one distance, while bifocals or trifocals provide two or three distinct zones; progressive lenses offer a gradual change in power without visible lines. Specialty options include photochromic lenses that darken in bright light and polarized lenses for glare reduction.

History and adoption: eyeglasses emerged in 13th-century Italy and gradually spread worldwide, with mass production and prescription accessibility expanding in the 19th and 20th centuries. Care and maintenance: glasses should be cleaned with a microfiber cloth and mild soap, stored in a protective case, and professionally adjusted if they become loose or uncomfortable. While primarily a vision aid, eyeglasses have also become a fashion item, with alternatives such as contact lenses and refractive surgery available for vision correction.