# reading a prescription Flashcards

spherical lens

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

cylindrical lens

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

we write the spherical number as

we write the spherical number as plano instead of writing “0.”

spherocylinder lens

If a lens has an astigmatism correction and a spherical correction for either myopia or hyperopia, it’s called a spherocylinder lens

Here are two samples of numbers you might see on a prescription:

Here are two samples of numbers you might see on a prescription:

O.D: +3.00 -2.00 x 090

O.S: -4.00 -0.75 x 110

The first set of numbers refers to …

The first set of numbers refers to the right eye (O.D.),

the second set of numbers refers to

the left eye (O.S.).

the first number for each eye always tells you what?

This number always tells you if the eye is nearsighted or farsighted. We call this number the sphere number, and it specifies a single plus or minus power in all directions.

the second set of numbers are called what?

These are called the cylinder numbers, and as you’ve

cylinder numbers we use them if an eye has what

if an eye has astigmatism.

cylinder power tells us the difference between what?

The cylinder power tells us the difference between the steepest axis of the eye and the flattest axis of the eye, which are generally separated by 90 degrees. Typically in the optical field, we write the astigmatism correction as a minus cylinder number. (We can also write this number in plus cylinder form—something we’ll talk about a little later.)

Typically in the optical field, we write the astigmatism correction as what?

as a minus cylinder number. We can also write this number in plus cylinder form

steepest axis of the eye and the flattest axis of the eye, which are generally separated by

by 90 degrees.

if there’s no astigmatism, you’ll see the abbreviation

sph for sphere or D.S. for diopters of sphere after the number Doctors add these letters to let other people know that there’s not supposed to be a cylinder number. Otherwise, they might think we just forgot to fill in this part of the prescription.

Why do we need to define the axis?

Why do we need to define the axis? Well, a spherical lens has the same effect on vision no matter which way it’s turned. But obviously, that’s not true for a cylindrical lens.