Stokes lens also known as variable power cross cylinder lens is a lens used to diagnose a type of

refractive error Refractive error is a problem with focus (optics), focusing light accurately on the retina due to the shape of the eye and/or cornea. The most common types of refractive error are myopia, near-sightedness, hyperopia, far-sightedness, astigmatis ...

known as

astigmatism Astigmatism is a type of refractive error due to rotational asymmetry in the eye's refractive power. The lens and cornea of an eye without astigmatism are nearly spherical, with only a single radius of curvature, and any refractive errors ...

Lens design

The Stokes lens also known as variable power cross cylinder lens, in its standard version, is a lens combination consisted of equal but opposite (one plano-convex and other plano-concave) power

cylindrical lens A cylindrical lens is a lens (optics), lens which Focus (optics), focuses light into a line instead of a point as a Lens (optics), spherical lens would. The curved face or faces of a cylindrical lens are sections of a Cylinder (geometry), cylinde ...

es attached together in a way so that the lenses be rotated in opposite directions. When the axes are parallel, the two powers cancel each other out to achieve the resulting power zero; When the axes are vertical, a sphero-cylindrical lens with maximum power is obtained.

Uses

Stokes lens is a lens used to diagnose and measure astigmatism.

Adaptations

American ophthalmologist Edward Jackson revised the Stokes lens concept and made a cross cylinder lens to refine power and axis of astigmatism. This lens combination is known as Jackson cross cylinder. Based on the Stokes lens, James P. Foley and Charles E. Campbell made a variable power astigmatic lens which is combination of two identical cylindrical powers instead of equal and opposite powers.

History

In 1837, English mathematician and astronomer

George Biddell Airy Sir George Biddell Airy (; 27 July 18012 January 1892) was an English mathematician and astronomer, as well as the Lucasian Professor of Mathematics from 1826 to 1828 and the seventh Astronomer Royal from 1835 to 1881. His many achievements inc ...

invented the cylindric lens and used it to correct astigmatism. Irish English physicist and mathematician George Stokes invented Stokes lens in 1849.

References

{{DEFAULTSORT:Stokes lens Diagnostic ophthalmology Optometry Lenses