A monocle is a type of corrective lens used to correct or enhance the visual perception in only one eye. It consists of a circular lens placed in front of the eye and held in place by the eye socket itself. Often, to avoid losing the monocle, a string or wire is connected to the wearer's clothing at one end and, at the other end, to either a hole in the lens or, more often, a wire ring around its circumference.
Joseph Chamberlain wearing a monocle
A 20th-century gold plated monocle with gallery
19th-century gold-filled quizzing glass
A corrective lens is a transmissive optical device that is worn on the eye to improve visual perception. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia. Glasses or "spectacles" are worn on the face a short distance in front of the eye. Contact lenses are worn directly on the surface of the eye. Intraocular lenses are surgically implanted most commonly after cataract removal but can be used for purely refractive purposes.
A pair of contact lenses, positioned with the concave side facing upward
Typical pair of single vision glasses
These bifocals are upside down as they rest on the surface. The add segment of the lens for near vision is the D-shaped area.
Prismatic color distortion shown with a camera set for nearsighted focus, and using -9.5 diopter eyeglasses to correct the camera's myopia.