How to calculate the degree of contact lenses

There is a conversion formula for the degree of frame lenses and contact lenses: Fo=Fs/(1-dFs)

Fo: contact lens prescription;

Fs: prescription of frame lens;

d: distance between frame lens and cornea

For example: the degree of the frame lens is -4.00D, and the distance between the frame and the contact lens is 12 mm, then the degree of the contact lens can be converted into Fo=4.00D/ [1-0.012 (-4.00)]=-3.82D, can be selected by -3.75D.

If the degree of the frame lens is 4.00D to 5.00D, the contact lens degree is: myopia minus 0.25D, hyperopia plus 0.25D.

If the degree of the frame plus mirror is 5.00D to 7.00D, the contact lens degree is: myopia minus 0.50D, hyperopia 0.50D.

If the degree of the frame plus mirror is 7.00D to 9.00D, the contact lens degree is: myopia minus 0.75D, hyperopia plus 0.75D.

If the degree of the frame lens is 9.00D to 11.00D, the contact lens degree is: myopia minus 1.00D, hyperopia plus 1.00D.