Work out eye prescription conversion instantly with clear inputs, formula shown and shareable results.
Transposes a spectacle prescription between plus and minus cylinder form and reports the spherical equivalent.
Transposition
New sphere = sphere + cylinder; new cylinder = cylinder with the sign reversed; new axis = axis plus or minus 90 degrees. Spherical equivalent = sphere + cylinder/2
Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
Optometrists usually write minus cylinder while some laboratories and ophthalmologists use plus cylinder; the lens is identical.
It condenses a sphere-cylinder prescription to a single number for screening, contact lens trials and epidemiology.