Refractive Errors

Question 1

What is the primary purpose of the eye?

Answer 1

To focus light on the retina.

Question 2

What eye part does light first enter?

Answer 2

Cornea.

Question 3

After the light travels through the cornea, where does light travel next?

Answer 3

It travels through the clear, aqueous fluid, and passes through the pupil.

Question 4

Why and how does the pupil change size?

Answer 4

The muscles in the iris relax or constricts, controlling the amount of light entering the eye

Question 5

After the light travels through the pupil, where does the light travel next?

Answer 5

Light is then focused on the crystalline lens

Question 6

What happens after light goes through the crystalline lens?

Answer 6

Proceeds to the viterous.

Question 7

When light proceeds to the viterous, where does it go next?

Answer 7

It proceeds to the viterous to reach the retina.

Question 8

What happens to the light rays when it reaches the retina?

Answer 8

In the retina, the light rays convert into electrical impulses that travels along the optic nerve to the brain, interpreted as an image.

Question 9

What are one of the ways to measure visual acuity?

Answer 9

The Snellen Chart.

Question 10

What does it mean when someone has a 20/20 vision?

Answer 10

When a person can see an object at twenty feet that normal person can see at twenty feet.
The patient can see at this feet/What a normal person would see at this feet

Question 11

What does it mean when someone has a 20/40 vision?

Answer 11

The larger the bottom number is being measured the poorer the vision is being measured.

Question 12

In the eye’s optical system, how much does the eye have total eye power?

Answer 12

Approx. 60 diopters.

Question 13

Where is the eye power generated?

Answer 13

In the cornea and crystalline lens.

Question 14

What happens if light isn’t bent properly?

Answer 14

If light isn’t bent properly, then the image doesn’t focus on the retina and there is a REFRACTIVE ERROR.

Question 15

Define emmetropia.

Answer 15

Emmetropia is an eye that focuses light precisely onto the retina with NO additonal assistance from eyeglasses or contact lens.

Question 16

What happens to the light rays when the eyes are myopic or nearsighted?

Answer 16

When it focuses an equal amount in FRONT of the retina, the light rays are no longer in focus by the time they reach the retina; happens when the cornea and/or crystalline lens generates too much plus power.

Question 17

What’s an example of a simple myopic Rx?

Answer 17

Rx. -2.00D

Question 18

What type of lens would help myopia?

Answer 18

A concave lens.

Question 19

What happens to the light rays when the eyes are hyperopic or farsighted?

Answer 19

When light rays focus behind the retina. Light doesn’t actually focus behind the retina. Rather at a points where light rays reach the retina, it has not yet reached a point focus. This may be because the globe of the eye is somewhat short or not enough plus power. Far objects are clear but not near.

Question 20

What’s an example of a simple hyperopic Rx?

Answer 20

Rx. +2.00D

Question 21

What type of lens would help hyperopia?

Answer 21

convex lens.

Question 22

What is astigmatism?

Answer 22

The refractive error that occurs when the light rays don’t come to a single focus, but instead focusing MORE than one point on the retina.

Question 23

Whats an example of astigmatic Rx?

Answer 23

Rx. -2.00 -0.75 x180.

The amount of astigmatism DOES NOT indicate the power of the other meridian, but indicates the amount astigmatism.

Question 24

How do you determine the power of the second meridian?

Answer 24

To add them together.

Question 25

What’s an example of a compound myopic astigmatism?

Answer 25

Rx. -2.25 -0.25 x180
-2.25(+)-0.25=-2.50 
Vertical Meridian: -2.50
Horizontal Meridian:-2.25
Since are ALL minus.

Question 26

What’s an example of a compound hyperopic astigmatism?

Answer 26

Rx. +2.50 -0.50 x180
\+2.50 (+) -0.50 =+2.00
Vertical Meridian:+2.00
Horizontal Meridian:+2.50
Since are ALL plus.

Question 27

What’s an example of a mixed astigmatism?

Answer 27

Rx. +1.00 -1.25  x180
\+1.00 (+) -1.25= -0.25
Vertical Meridian:-0.25
Horizontal Meridian:+1.00
One of the eyes focal point is in front of the retina while the other is behind the retina.

Question 28

What is presbyopia?

Answer 28

When the crystalline becomes denser and loses its ability to change shape and focus objects at different distances.

Question 29

How do you correct presbyopia eyes?

Answer 29

Bifocal or multifocal lenses are designated in a written Rx with an add power along with sphere, cylinder, axis.
The add power has to be the same for both eyes.

Question 30

What range of add power in quarter diopters?

Answer 30

Between +1.00D and +2.50D.

Question 31

On presbyopia lenses, how is the power written in a the Rx?

Answer 31

The add power is not written on Rx but rather the add power is added to the distance sphere power only.
The cylinder and the axis remains unchanged.

Question 32

What is an example of a presbyopic Rx?

Answer 32

-3.00 -1.00 x180; +2.00D Add
Distance -3.00 -1.00 x180
Near -1.00 -1.00 x180