# formulas Flashcards

nominal power

F1+F2=Ftotal

steps for transposing from one form to the other

- add the sphere and cylinder values to obtain the new sphere value
- change the sign of the cylinder(plus to minus or minus to plus)
- change the axis by 90 degrees (this can be by addition or subtraction since the end result is the same. The answer for the axis must be from 1 to 180 degrees. an answer of 190 is unacceptable.

O.D. stands for?

O.D. stands for oculus dextrus, meaning right eye in Latin.

• O.S. stands for?

• O.S. stands for oculus sinister, meaning left eye in Latin.

meridians.

These are imaginary lines that help us describe the location of the axis powers of a lens with a correction for astigmatism.

spherical lens

In this type of lens, the power is the same in all directions.

cylindrical lens.

This type of lens looks like a vertical slice cut from the flattest surface of a grape.

sphere number

first number for each eye. This number always tells you if the eye is nearsighted or farsighted. We call this number

and it specifics a single plus or minus power in all directions.

plus lens

means that the eye is hyperopic or farsighted.

minus lens

This means that the left eye is nearsighted or myopic

second set of numbers?

These are called the cylinder numbers, and as you’ve seen, we use them if an eye has astigmatism.

final set of numbers for each eye.

This set of numbers describes the direction in which the person’s cornea is the flattest, causing the astigmatism. We call this number the axis or the axis of the astigmatism.

sph for sphere or D.S.

some people don’t have an astigmatism, so not all prescriptions will have this second part. If there’s no astigmatism, you’ll see the abbreviation sph for sphere or D.S. for diopters of sphere after the number,

The first set of numbers

refers to the right eye (O.D.)

the second set of numbers

refers to the left eye (O.S.).