Optical glasses use lenses, prisms, contact lenses, artificial lenses, etc. to correct vision, eliminate visual fatigue, and protect or treat eyes.
There are many types of glasses. There are optical glasses and contact glasses for correcting refractive errors. In addition to contact glasses, intraocular lenses can be implanted for correcting aphakia. In addition, there are various protective glasses, beauty glasses, and vision aids to correct low vision. All lenses are thin lenses, and the degree is the reciprocal of the focal length of the lens.
Lens lenses are divided into spherical lenses and cylindrical lenses. The curved surface of the spherical lens is a part of the spherical surface, and is divided into a convex spherical lens or a concave spherical lens according to the convergence or separation of parallel light rays.
Convex spherical lenses are used to correct hyperopia, presbyopia or aphakia. Concave spherical lenses are used to correct nearsightedness. The curved surface of the cylindrical lens is a part of the cylinder. The axis of the cylindrical lens is parallel to the cylinder. There is no refractive power in the direction of the axis and perpendicular to the axis. The directional refractive power is the largest, and it is divided into convex cylindrical lenses or concave cylindrical lenses, which are used to correct hyperopia or myopia astigmatism, respectively.