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clinic 1 > astigmatism > Flashcards

astigmatism Flashcards

1
Q

When parallel rays of light enter the eye (with accommodation relaxed) and do not come to a single point focus on or near the retina

A

astigmatism

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2
Q

causes of astigmatism

A
  1. the cornea has unequal curvature on its anterior surface
  2. the lens has unequal curvature on its surface or layers
  3. due to distortion of cornea or the lens
  4. refracting power is not uniform in all meridians
  5. the principal meridians are the meridians of greatest and least refracting powers
  6. the amount of astigmatism is equal to the difference in refracting power of the two principal meridians
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3
Q

classifications of astigmatism

A

Based on etiology
Based on relation between principal meridians
Based on orientation of meridian or axis
Based on focal points relative to the retina
Based on relative locations of principal meridians or axes when comparing the two eyes

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4
Q

when the cornea has unequal curvature on the anterior surface

A

corneal astigmatism

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5
Q

when the crystalline lens has unequal curvature on the surface or on its layer

A

lenticular astigmatism

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6
Q

The sum of corneal astigmatism and residual astigmatism

A

total astigmatism

(Total Astigmatism = corneal + residual)

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7
Q

under total astigmatism

A

posterior corneal surface
lenticular surface
lenticular zonule

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8
Q

3 types of regular astigmatism

A

with the rule
against the rule
oblique

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9
Q

when the two principal meridians are perpendicular to each other

A

regular astigmatism

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10
Q

When the greatest refractive power is within 30 of the vertical meridian (i.e., between 60 and 120 meridians)
The most common type of astigmatism based on the orientation of meridians
Minus cylinder axis around horizontal meridian

A

with the rule astigmatism

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11
Q

When the two principal meridians are not perpendicular to each other
Curvature of any one meridian is not uniform
Associated with trauma, disease, or degeneration
VA is often not correctable to 20/20

A

irregular astigmatism

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12
Q

When one of the principal meridians is focused on the retina and the other is not focused on the retina (with accommodation relaxed)

A

simple astigmatism

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13
Q

When one of the principal meridians is focused in front of the retina and the other is focused on the retina (with accommodation relaxed)

A

simple myopic astigmatism

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14
Q

When one of the principal meridians is focused behind the retina and the other is focused on the retina (with accommodation relaxed)

A

simple hyperopic astigmatism

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15
Q

When both principal meridians are focused either in front or behind the retina (with accommodation relaxed)

A

compound astigmatism

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16
Q

when both principal meridians are focused in front of the retina with accommodation relaxed

A

compound myopic astigmatism

17
Q

When both principal meridians are focused behind the retina (with accommodation relaxed)

A

compound hyperopic astigmatism

18
Q

When one of the principal meridians is focused in front of the retina and the other is focused behind the retina (with accommodation relaxed)

A

mixed astigmatism

19
Q

The principal meridians or axes of the two eyes are symmetrical (e.g., both eyes are WTR or ATR)
The sum of the two axes of the two eyes equals approximately 180
example:

OD: pl -1.00 x 175
OS: pl -1.00 x 005

A

symmetrical astigmatism

20
Q

The principal meridians or axes of the two eyes are not symmetrical (e.g., one eye is WTR while the other eye is ATR)
The sum of the two axes of the two eyes does not equal approximately 180

A

asymmetrical astigmatism

21
Q

older adults shift towards __ astigmatism

A

ATR

22
Q

infants are born with ___ astigmatism, where the cornea is the source of astigmatism

A

ATR

23
Q

teenagers shift towards ______ astigmatism

A

WTR

24
Q

preschool children have little to no astigmatism

A
25
Q

asian infants are ____ astigmatism

A

WTR

26
Q

caucasian infants are ____ astigmatism

A

ATR

27
Q

presence of astigmatism symptoms

A

distorted vision at distance and near
letter confusion
asthenopia (ocular fatigue)
headaches
squinting

28
Q

common cause of ocular fatigue

A

frequent squinting to clear distorted vision

29
Q

presence of astigmatism signs

A

decreased visual acuity at distance and near

30
Q

clinical tests for astigmatism

A

monocular subjective refraction
retinoscopy
keratometry
autorefraction
VA tests for distance and near

31
Q

it is the most reliable source of information for cylinder power and axis

A

retinoscopy

32
Q

astigmatism management

A

spectacle
contact lens
refractive surgery

33
Q

refractive surgeries

A

Photorefractive keratectomy (PRK)
Laser assisted in-situ keratomileusis (LASIK)

34
Q

CL types for astigmatism

A

Toric soft contact lenses
Toric rigid gas permeable contact lenses

35
Q

is a refractive error of the eye in which there is a difference in degree of refraction in different meridians, the eye has different focal points in different planes

A

astigmatism

36
Q

Most astigmatic corneas have two curves, ________ and _____ . This causes light to focus on more than one point in the eye resulting in blurred vision. The cornea is normally spherical although In people with astigmatism it may be shaped like a rugby ball or oval instead of tennis ball In astigmatism the front surface of

A

steeper curve
flatter curve

clinic 1 (4 decks)

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