​What are optical glasses

Lenses are divided into spherical lenses and cylindrical lenses. The curved surface of the spherical lens is a part of the spherical surface. It is divided into convex spherical lens or concave spherical lens according to how it aggregates or separates parallel light rays.

Convex spherical lenses are used to correct hyperopia, presbyopia or aphakia. Concave spherical lenses are used to correct myopia. The curved surface of the cylindrical lens is part of the cylinder. The axis of the cylindrical lens is parallel to the cylinder. It has no refractive power in the direction of the axis and is perpendicular to the axis. The direction of refractive power is the largest, and they are divided into convex cylindrical lenses or concave cylindrical lenses, which are used to correct farsightedness or myopic astigmatism respectively.