reading a prescription

Question 1

spherical lens

Answer 1

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

Question 2

cylindrical lens

Answer 2

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

Question 3

we write the spherical number as

Answer 3

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

Question 4

spherocylinder lens

Answer 4

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

Question 5

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

Answer 5

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

Question 6

The first set of numbers refers to …

Answer 6

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

Question 7

the second set of numbers refers to

Answer 7

the left eye (O.S.).

Question 8

the first number for each eye always tells you what?

Answer 8

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.

Question 9

the second set of numbers are called what?

Answer 9

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

Question 10

cylinder numbers we use them if an eye has what

Answer 10

if an eye has astigmatism.

Question 11

cylinder power tells us the difference between what?

Answer 11

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.)

Question 12

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

Answer 12

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

Question 13

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

Answer 13

by 90 degrees.

Question 14

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

Answer 14

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.

Question 15

Why do we need to define the axis?

Answer 15

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.

Question 16

The majority of lens diopters you’ll encounter are in increments of how much?

Answer 16

0.25 diopters of power. Very seldom will you see diopters in increments of 0.12 diopters, although you may. So think of the diopters of power like amounts of currency, with quarters as the smallest increment.

Question 17

When optometrists like me write prescriptions, they use what?

Answer 17

minus (negative) cylinder form.

Question 18

When ophthalmologists write prescriptions, they use what?

Answer 18

they use plus (positive) cylinder form.

Question 19

the steps for transposition.

Answer 19

Step 1: Take the sphere number (including the sign) and the cylinder number (including the sign), and add them together to get your new sphere.

Step 2: Take the cylinder number, and change its sign to the opposite sign to come up with the new cylinder.

Step 3: Take the axis, and change it 90 degrees by either adding 90 or subtracting 90 from it. Remember that the axis cannot be 0 or greater than 180. This will tell you whether to add or subtract.

Question 20

how to use an optical cross.

Answer 20

Here’s how to use an optical cross.
First, you’ll clock the front of the lens in two directions. (This will give you the highest and lowest powers for the front of the lens.) Let’s say the front of the lens is spherical, so you get the same number—+800—in the horizontal (180-degree) and vertical (90-degree) meridians. But when you follow the same steps for the back of the lens, you come up with two different powers:

Question 21

As an optician, you’ll sometimes encounter crooked frames that cause the axis of the astigmatism to wind up in the wrong place. As a result, your client will have the wrong power in front of his or her eyes. (We call this what?

Answer 21

induced astigmatism.)

Question 22

Simple myopic astigmatism.

Answer 22

This is when there is no astigmatism in one meridian, and 90 degrees away from that meridian, the eye is nearsighted.

Question 23

Simple hyperopic astigmatism.

Answer 23

In this type, the eye is normal in one meridian. In the other meridian, 90 degrees away, it’s farsighted.

Question 24

Compound myopic astigmatism.

Answer 24

Here, the eye is nearsighted in both meridians. However, it’s more nearsighted in one meridian than the other.

Question 25

Compound hyperopic astigmatism.

Answer 25

In this type of astigmatism, the eye is farsighted in both meridians, but it’s more farsighted in one meridian than the other.

Question 26

Mixed astigmatism.

Answer 26

Mixed astigmatism. In this case, one meridian is nearsighted, and the other is farsighted.