Brainscape's Knowledge GenomeTM

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


See full index

Contact Lens (MIDTERM | 2ND SEM) > Astigmatism > Flashcards

Astigmatism Flashcards

1
Q

it is the difference in refractive power between the
two principal meridians of the eye

A

astigmatism

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

The greater the curvature the:

A

greater the power

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

two meridians of the eye

A

power meridian
axis meridian

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

meridian of greatest optical power

A

power meridian

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

meridian of least optical power

A

axis meridian

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

Meridian Descriptions

A

Refractive Power (Dioptres)
Radius of Curvature (mm)

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

Causes of astigmatism

A

Meridional differences in curvature and/or flattening rates of cornea, crystalline lens, and refractive index of optical components

Shape of posterior pole

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

Astigmatism Classification

A

● Simple hyperopic astigmatism
● Compound hyperopic astigmatism
● Simple myopic astigmatism
● Compound myopic astigmatism
● Mixed astigmatism

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

Structural classification of astigmatism

A

Corneal
Lenticular
Other internal astigmatism
Total

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

most common classification of astigmatism

A

corneal astigmatism

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

Classification of astigmatism where the crystalline lens has a problem

A

lenticular astigmatism

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

Total Astigmism =

A

Internal + External

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

In corneal astigmatism cornea is seldom ________

A

spherical

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

True corneal astigmatism must include ___________
this neutralizes 10-14% of anterior astigmatism

A

posterior

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

optical description

A

corneal astigmaism

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

anatomical description

A

corneal toricity

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

Lenticular astigmatism is due to differences in

A
  • meridional refractive powers
  • refractive indices of lens layers
  • surface flattening rates of lens layers
  • symmetry of lens
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Lenticular astigmatism is caused by tilting and/or decentration of __________________

A

crystalline lens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Internal astigmatism

The retina may be:

A
  • toric in shape
  • tilted
  • decentred
20
Q

Total Astigmatism is the combination of

A

● Corneal astigmatism
● Lenticular astigmatism
● Other internal astigmatism

21
Q

Astigmatism where the principal meridian is 90deg apart

A

Regular

22
Q

Astigmatism that is often acquired or decondary to trauma or disease

regular or irregular

A

irregular

23
Q

CAUSES IRREGULAR ASTIGMATISM

A
  • Disease/Degeneration
  • Diabetes
  • Distortion of refractive surface
  • Irregularities of refractive indices
  • Scar
24
Q

Types of regular astigmatism

A

WTR
ATR
Oblique

25
Q

Ocular astigmatism in which the refractive power of the vertical (or near vertical) meridian is the greatest

A

WTR

26
Q

Correcting minus cylinder axis 0-30°, 150-180°

A

WTR

27
Q

Ocular astigmatism in which the refractive power of the horizontal (or near horizontal) meridian is the greatest

A

ATR

28
Q

Correcting minus cylinder axis 60-120°

A

ATR

29
Q

Astigmatism in which the two principal meridians lie somewhere between the axes defining either WTR or ATR astigmatism

A

Oblique

30
Q

Correcting minus cylinder axis 31-59°, 121-149°

A

oblique

31
Q

ASTIGMATISM REFRACTIVE CYLINDER
Classification by magnitude

≤ 0.75 D Cyl

A

Negligible

32
Q

ASTIGMATISM REFRACTIVE CYLINDER
Classification by magnitude

1.00 to 1.50 D Cyl

A

Low

33
Q

ASTIGMATISM REFRACTIVE CYLINDER
Classification by magnitude

1.75 to 2.50 D Cyl

A

Moderate

34
Q

ASTIGMATISM REFRACTIVE CYLINDER
Classification by magnitude

> 2.50 D Cyl

A

High

35
Q

ASTIGMATISM INCIDENCE SHIFT WITH AGE

ATR -> OBLIQUE/WTR

A

INFANTS

36
Q

ASTIGMATISM INCIDENCE SHIFT WITH AGE

ADULTS

A

WTR -> ATR/OBLIQUE

37
Q

ASTIGMATISM COMPONENTS

A

TOTAL
CORNEAL
LENTICULAR/INTERNAL

38
Q

JAVAL’S RULE

A

If ATR
Total = 1.25 (Ac) - 0.50

If WTR
Total = 1.25 (Ac) + 0.50

39
Q

Grosvenor et al rule for WTR

A

T = Ac + 0.50

40
Q

Grosvenor et al rule for ATR

A

T = AC - 0.50

41
Q

Measurement of astigmatism

front surface curvature

A

keratometer
photokeratoscopy
computer-assisted corneal mapping system

42
Q

Measurement of astigmatism

back surface curvature

A

purkinje images

43
Q

\ defined as the astigmatic refractive error that is present when a contact lens is placed upon the cornea to correct the existing ametropia.

A

residual astigmatism

44
Q

PHYSIOLOGICAL RESIDUAL ASTIGMATISM

A

● Unneutralized corneal astigmatism
● Posterior corneal astigmatism
● Lenticular astigmatism
● Tilted crystalline lens
● Refractive index anomalies
● Oblique aberrations
● Misalignment of component

45
Q

INDUCED RESIDUAL ASTIGMATISM

A

● Tilted and/or decentred CL
● Toricity and/or bitoricity of CL
● CL mislocation (rotation)
● Warpage and/or flexure of CL

Contact Lens (MIDTERM | 2ND SEM) (6 decks)

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