Astigmatism

Question 1

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

Answer 1

Astigmatism

Question 2

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

resulting to having multiple foci

Answer 2

Astigmatism

Question 3

Considered to be the most common refractive error corrected today

Answer 3

Astigmatism

Question 4

meridian with least power

Answer 4

Axis meridian

Question 5

meridian with greatest power

Answer 5

Power meridian

Question 6

axis and power meridian are ____ degrees apart

Answer 6

90 degrees

Question 7

• 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.

Answer 7

Thomas Young

Question 8

First to correct astigmatism by spherocylindrical lens

Answer 8

George Biddle Airy

Question 9

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

Answer 9

USA 1828

Question 10

Produced the first distance test chart for astigmatism

created the clock dial chart

Answer 10

John Green

Question 11

Credited for the first trial case containing cylindrical lenses

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

Answer 11

H. Knapp

Question 12

Etiology / causes of astigmatism:

Answer 12

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

Question 13

Symptoms of astigmatism:

Answer 13

• 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

Question 14

Signs of astigmatism:

Answer 14

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

Question 15

Classification of Astigmatism:

Answer 15

• Total / Physiologic astigmatism
• Corneal Astigmatism
• Lenticular Astigmatism

Question 16

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

Answer 16

Regular Type astigmatism

Question 17

type of astigmatism not at right angle to each other

curvature is not uniform

Answer 17

Irregular Type

Question 18

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

60deg to 120deg

Answer 18

With-the-Rule astigmatism / Direct astigmatism

Question 19

type of astigmatism wherein curvature of the greatest power lies within

0 - 30 degrees

150 - 180 degrees

Answer 19

Against-the-rule astigmatism / Inverse or Perverse astigmatism

Question 20

type of astigmatism wherein Greatest power lies in:

30 - 60 degrees

120 - 150 degrees

Answer 20

Oblique Astigmatism

Question 21

astigmatism referring to both corneas:

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

Answer 21

Symmetric astigmatism

Question 22

astigmatism referring to both corneas:

astigmatism when the two is not equal to 180 degrees

Answer 22

Asymmetric Astigmatism

Question 23

astigmatism referring to both corneas:

both astigmatism are WTR or both are ATR

Answer 23

Homonymous Astigmatism

Question 24

Symmetric astigmatism if both WTR

Answer 24

Homologous Symmetric Astigmatism

Question 25

Symmetric Astigmatism if both ATR

Answer 25

Heterologous Symmetric Astigmatism

Question 26

astigmatism referring to both corneas: one eye is WTR and the other eye is ATR

Answer 26

Heteronymous astigmatism

Question 27

With accommodation completely relaxed, the 2 principal meridians tend to fall beyond the retina Correction is Plus sphere with Plus cylinder lens

Answer 27

Compound Hyperopic Astigmatism

Question 28

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

Answer 28

Simple Hyperopic Astigmatism

Question 29

with accommodation relaxed, both principal meridians would focus in front of retina Correction will require minus sphere combined with minus cylinder

Answer 29

Compound Myopic Astigmatism

Question 30

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

Answer 30

Simple myopic astigmatism

Question 31

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

Answer 31

Mixed Astigmatism

Question 32

mixed astigmatism wherein cylinder is stronger than sphere

Answer 32

Contrageneric mixed astigmatism

Question 33

mixed astigmatism wherein cylinder is weaker than sphere

Answer 33

Congeneric Mixed astigmatism