| Stokes lens | |
| Test Of: | Astigmatism |
| Synonyms: | Stokes' lens |
Stokes lens also known as variable power cross cylinder lens[1] is a lens used to diagnose a type of refractive error known as astigmatism.
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 lenses attached together in a way so that the lenses be rotated in opposite directions.[2] 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.
Stokes lens is a lens used to diagnose and measure astigmatism.[3] [4]
American ophthalmologist Edward Jackson revised the Stokes lens concept and made a cross cylinder lens to refine power and axis of astigmatism.[2] This lens combination is known as Jackson cross cylinder.[2] 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.[2] [5]
In 1837, English mathematician and astronomer George Biddell Airy invented the cylindric lens and used it to correct astigmatism.[6] Irish English physicist and mathematician George Stokes invented Stokes lens in 1849.[6]