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Refractive Errors > Astigmatism > Flashcards

Astigmatism Flashcards

1
Q
  • refractive condition in which a point focus of light cannot be formed on the retina
  • having multiple foci
A

Astigmatism

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2
Q

it exist because of variation in powers in the different meridians of the eye

resulting to having multiple foci

A

Astigmatism

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3
Q

Considered to be the most common refractive error corrected today

A

Astigmatism

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4
Q

meridian with least power

A

Axis meridian

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5
Q

meridian with greatest power

A

Power meridian

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6
Q

axis and power meridian are ____ degrees apart

A

90 degrees

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7
Q
  • HE had a crude measurement of his own astigmatism about 1.75D
  • The value remained when he immersed his
    head underwater (thus eliminating the
    influence of cornea) which he attributed to
    the lens.
A

Thomas Young

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8
Q

First to correct astigmatism by spherocylindrical lens

A

George Biddle Airy

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9
Q

first lens was made to correct astigmatism in united states in this period

A

USA 1828

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10
Q

Produced the first distance test chart for astigmatism

created the clock dial chart

A

John Green

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11
Q

Credited for the first trial case containing cylindrical lenses

suggested the method that we now use for the location of axis

A

H. Knapp

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12
Q

Etiology / causes of astigmatism:

A

Different Corneal curvature

Different lenticular curvature

traction of the external muscles which exerted the scleral coat

Eccentric position of fovea in relation to visual axis

Changes in vitreous gel w/c results in a change in index of refraction

Irregularity in surface of retina

Angle alpha may cause against-the-rule astigmatism of 0.50 to 0.75 D

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13
Q

Symptoms of astigmatism:

A
  • Blurred Vision
  • Transient blurring of vision (due to constant accommodation)
  • Headaches (frontal or temporal) - from effort to accommodate in attempt to clear the remaining blurred vision
  • Tearing and smarting
  • Tiring of the eyes
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14
Q

Signs of astigmatism:

A
  • Tilting of the head
  • Squinting of the eyes
  • Wrinkling and furrowing of brows
  • Holding reading material too close
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15
Q

Classification of Astigmatism:

A
  • Total / Physiologic astigmatism
  • Corneal Astigmatism
  • Lenticular Astigmatism
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16
Q

type of astigmatism which 2 principal meridians are at right with each other

A

Regular Type astigmatism

17
Q

type of astigmatism not at right angle to each other

curvature is not uniform

A

Irregular Type

18
Q

type of astigmatism wherein curvature of the greatest power lies nearest to the vertical meridian

60deg to 120deg

A

With-the-Rule astigmatism / Direct astigmatism

19
Q

type of astigmatism wherein curvature of the greatest power lies within

0 - 30 degrees

150 - 180 degrees

A

Against-the-rule astigmatism / Inverse or Perverse astigmatism

20
Q

type of astigmatism wherein Greatest power lies in:

30 - 60 degrees

120 - 150 degrees

A

Oblique Astigmatism

21
Q

astigmatism referring to both corneas:

total of degrees between 2 weakest or 2 strongest is equal to 180

A

Symmetric astigmatism

22
Q

astigmatism referring to both corneas:

astigmatism when the two is not equal to 180 degrees

A

Asymmetric Astigmatism

23
Q

astigmatism referring to both corneas:

both astigmatism are WTR or both are ATR

A

Homonymous Astigmatism

24
Q

Symmetric astigmatism if both WTR

A

Homologous Symmetric Astigmatism

25
Q

Symmetric Astigmatism if both ATR

A

Heterologous Symmetric Astigmatism

26
Q

astigmatism referring to both corneas:

one eye is WTR and the other eye is ATR

A

Heteronymous astigmatism

27
Q

With accommodation completely relaxed, the 2 principal meridians tend to fall beyond the retina

Correction is Plus sphere with Plus cylinder lens

A

Compound Hyperopic Astigmatism

28
Q

with accommodation relaxed, one meridian is focus on the retina while the other would tend to focus behind the retina

Correction would consist of simple plus cylinder

A

Simple Hyperopic Astigmatism

29
Q

with accommodation relaxed, both principal meridians would focus in front of retina

Correction will require minus sphere combined with minus cylinder

A

Compound Myopic Astigmatism

30
Q

with accommodation relaxed, one meridian is focused on the retina while the other is in front of it

correction will require a simple minus cylinder

A

Simple myopic astigmatism

31
Q

with accommodation relaxed, one meridian tends to focus behind the retina while the other focuses in front of retina

A

Mixed Astigmatism

32
Q

mixed astigmatism wherein cylinder is stronger than sphere

A

Contrageneric mixed astigmatism

33
Q

mixed astigmatism wherein cylinder is weaker than sphere

A

Congeneric Mixed astigmatism

Refractive Errors (4 decks)

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