Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

OT > Refractive Error > Flashcards

Refractive Error Flashcards

1
Q

How much of the USA population is myopic?

A

42%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How much of the population has atigmatism?

A

40%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

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

A

50%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

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

A
  1. Cataract
  2. Uncorrected refractice error
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

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

What if it is refracted too little?

A

Refractive Myope

Refractive Hyperope

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Is most myopia axial or refractive?

A

Axial

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the focal point?

A

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).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Where is the focal point of a plus lens?

A

Behind the lens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Where is the focal point of a minus lens?

A

In front of the lens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the lens power?

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

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Where does the image lie for a plus lens?

A

Behind the lens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

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?

A

Incident= Neg
Emergent= Pos

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is l?

A

Location of object

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is l’ ?

A

Location of image

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the far point of the eye?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What happens if the object is at the far point?

What if the object is on the retina?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

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

How do you calculate the far point?

A

In front of the eye

1/refractive error in diopters

18
Q

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

How do you calculate the far point?

A

Behind the eye

1/ refractive error in diopters

19
Q

How does a correcting lens work?

A

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

20
Q

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

A

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

21
Q

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

A

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

22
Q

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

A

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

23
Q

What occurs in myopia?

A

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

24
Q

What must the lens power be equal to?

A

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

25
Q

How does accommodation occur?

A

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

26
Q

How is TOTAL HYPEROPIA measured?

A

By getting rid of all accommodation with a cycloplegic drug

27
Q

How is MANIFEST HYPEROPIA measured?

A

Finding the maximum plus lens that gives the best VA

28
Q

What is latent hyperopia?

A

Latent= Total Hyperopia- Manifest Hyperopia

29
Q

How is facultative hyperopia found?

A

Hyperopia under fog- hyperopia before fogging

30
Q

What is absolute hyperopia?

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

A

The amount of hyperopia that exceeds the maximum accommodation

3D of absolute hyperopia

31
Q

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

A

Cylinder Axis

32
Q

How do you transpose between minus cyl and plus cyl?

+1.00-4.00x180 convert to plus cyl.

A

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

33
Q

What is the required focal length?

A

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

34
Q

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

A

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

35
Q

Where is the first focal length of the eye?

A

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.

36
Q

What is the secondary focal length of the eye

A

The axial length when viewing an object at infinity

37
Q

Where is the second focal point of the lens?

A

When the object is at infinity

38
Q

Where is the 1st focal point of the lens?

A

When the image is at infinity

39
Q

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)

A
  1. Calculate power of the eye
    1/3.25= -(307.69+14)= -321.69mm

F= 1.333/0.02175 - - 1/0.32169
= 64.40D

  1. Calculate the axial length of the eye when focused at an object at infinity
    1.333/l’ - 1/infinity= 64.40D

l’= 20.70mm

40
Q

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

A

BVD!!!

OT (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions