Flashcards in reading a prescription Deck (26)

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1

## spherical lens

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

2

## cylindrical lens

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

3

## we write the spherical number as

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

4

## spherocylinder lens

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

5

##
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

6

## The first set of numbers refers to ...

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

7

## the second set of numbers refers to

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the left eye (O.S.).

8

##
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.

9

## the second set of numbers are called what?

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

10

## cylinder numbers we use them if an eye has what

### if an eye has astigmatism.

11

## 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.)

12

## 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

13

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

### by 90 degrees.

14

## 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.

15

## 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.

16

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

### 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.

17

## When optometrists like me write prescriptions, they use what?

###
minus (negative) cylinder form.

18

##
When ophthalmologists write prescriptions, they use what?

###
they use plus (positive) cylinder form.

19

##
the steps for transposition.

###

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.

20

##
how to use an optical cross.

###
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:

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?

###
induced astigmatism.)

22

## Simple myopic astigmatism.

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

23

##
Simple hyperopic astigmatism.

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

24

## Compound myopic astigmatism.

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

25

## Compound hyperopic astigmatism.

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

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