Refractive Error

Question 1

How much of the USA population is myopic?

Answer 1

42%

Question 2

How much of the population has atigmatism?

Answer 2

40%

Question 3

By 2050 how much of the world’s population will be myopic?

Answer 3

50%

Question 4

What is the #1/ #2 leading causes of blindness worldwide?

Answer 4

1. Cataract
2. Uncorrected refractice error

Question 5

What happens if an eye has the same axial length but the light is refracted too much?

What if it is refracted too little?

Answer 5

Refractive Myope

Refractive Hyperope

Question 6

Is most myopia axial or refractive?

Answer 6

Axial

Question 7

What is the focal point?

Answer 7

When rays from a distant object strike a lens, the image is formed at the focal point of the lens (F). The distance from the lens to the focal point is called the focal length of the lens (f).

Question 8

Where is the focal point of a plus lens?

Answer 8

Behind the lens

Question 9

Where is the focal point of a minus lens?

Answer 9

In front of the lens

Question 10

What is the lens power?

Ie: Focal length 1m=?
f= 0.5m=?

Answer 10

The power of a lens is stated as the reciprocal of the focal length in meters. Lens power is measured in DIOPTERS (D)

1m= 1D
0.5m= 2D

Question 11

Where does the image lie for a plus lens?

Answer 11

Behind the lens

Question 12

What sign do distances on the incident side have?

What sign do distance on the emergent side have?

What happens if you reverse where the object is?

Answer 12

Incident= Neg
Emergent= Pos

Does not matter! Incident side is always negative while the emergent side is always positive

Question 13

What is l?

Answer 13

Location of object

Question 14

What is l’ ?

Answer 14

Location of image

Question 15

What is the far point of the eye?

Answer 15

The far point of the eye is the point conjugate with the retina of the unaccommodated eye

Question 16

What happens if the object is at the far point?

What if the object is on the retina?

Answer 16

If the object is at the far point of the eye then the image is on the retina

If the object is on the retina then the image lies at the far point

Question 17

Where is the far point (Mr) of a myopic eye?

How do you calculate the far point?

Answer 17

In front of the eye

1/refractive error in diopters

Question 18

Where is the far point (Mr) of a hyperopic eye?

How do you calculate the far point?

Answer 18

Behind the eye

1/ refractive error in diopters

Question 19

How does a correcting lens work?

Answer 19

Any refractive error can be corrected by a lens whose second focal point coincides with the patient’s far point

Question 20

Where is the image in relation to the lens when the object is at optical infinity?

Answer 20

When the object is at optical infinity the image lies at the second focal point of the lens

Question 21

Where is the object in relation to the lens when the image is at optical infinity?

Answer 21

When the image is at infinity, the object lies at the first focal point of the lens

Question 22

Where is the second focal point of a plus lens?
Where is the second focal point of a minus lens?

Answer 22

Plus= Behind the lens
Minus= In front of the lens

Question 23

What occurs in myopia?

Answer 23

Parallel rays of light from a distant object are focused in front of the retina = blurred retinal image

Question 24

What must the lens power be equal to?

Answer 24

The lens power must be equal to the distance from the lens to the far point

Question 25

How does accommodation occur?

Answer 25

Increasing the refractive power of the crystalline lens resulting from contraction of the ciliary muscle

Question 26

How is TOTAL HYPEROPIA measured?

Answer 26

By getting rid of all accommodation with a cycloplegic drug

Question 27

How is MANIFEST HYPEROPIA measured?

Answer 27

Finding the maximum plus lens that gives the best VA

Question 28

What is latent hyperopia?

Answer 28

Latent= Total Hyperopia- Manifest Hyperopia

Question 29

How is facultative hyperopia found?

Answer 29

Hyperopia under fog- hyperopia before fogging

Question 30

What is absolute hyperopia? What is the absolute hyperopia for a +8.00 hyperope with a maximum accommodation of 5D?

Answer 30

The amount of hyperopia that exceeds the maximum accommodation 3D of absolute hyperopia

Question 31

What is the name of the direction of the zero power?

Answer 31

Cylinder Axis

Question 32

How do you transpose between minus cyl and plus cyl? +1.00-4.00x180 convert to plus cyl.

Answer 32

+1.00-4.00x180 -> -3.00+4.00x090

Question 33

What is the required focal length?

Answer 33

The distance from the lens to the far point of the eye

Question 34

When writing an Rx, how is the axis of the Rx determined?

Answer 34

The axis is determined by the most plus or least minus axis

Question 35

Where is the first focal length of the eye?

Answer 35

The distance from the eye to the far point or from the eye to to secondary focal point of the lens (calculate in bvd) REMEMBER: The correcting lens' secondary focal point coincides with the patient's far point.

Question 36

What is the secondary focal length of the eye

Answer 36

The axial length when viewing an object at infinity

Question 37

Where is the second focal point of the lens?

Answer 37

When the object is at infinity

Question 38

Where is the 1st focal point of the lens?

Answer 38

When the image is at infinity

Question 39

Calculate the second focal length of the eye when the eye has an AL= 21.75mm and can be fully corrected for distance by a -3.25sph (bvd=14mm)

Answer 39

1. Calculate power of the eye 1/3.25= -(307.69+14)= -321.69mm F= 1.333/0.02175 - - 1/0.32169 = 64.40D 2. Calculate the axial length of the eye when focused at an object at infinity 1.333/l' - 1/infinity= 64.40D l'= 20.70mm

Question 40

When calculating the power of the eyes from a glasses Rx what do you need to consider?

Answer 40

BVD!!!