A device designed for ophthalmic functions converts a damaging cylindrical lens prescription to its optimistic counterpart. For instance, a prescription of -2.00 sphere, -1.00 cylinder, and 90 axis may be transposed to -1.00 sphere, +1.00 cylinder, and 180 axis. This transposition represents the identical corrective energy however expressed in a different way.
This conversion gives a number of sensible benefits in optometry and ophthalmology. Transposing to plus cylinder permits for simpler lens fabrication in some situations and might simplify particular calculations associated to lens mixtures and prescriptions. Traditionally, totally different regional preferences and manufacturing strategies contributed to using both plus or minus cylinder notation, necessitating a technique for readily changing between the 2 varieties. This stays related in the present day for worldwide communication and consistency in lens prescriptions.