Astigmatism

Question 0

.Det WTR astigmatism

Answer 0

Minus cyl Rx w/ axis within 30 deg of 180

Question 1

.Types of astigmatism (based on locations of meridians)

Answer 1

1) Simple - One meridian on retina (0 power) / Other meridian in front of retina (if myopic), behind retina (if hyperopic)
2) Compound - Both meridians in front of retina (if myopic), behind retina (if hyperopic)
3) Mixed - One meridian in front of retina (if myopic) and other meridian behind retina (if hyperopic)

Question 2

.Convert plus cyl to minus cyl

Answer 2

1) Add sph + cyl
2) Change + cyl to - cyl sign
3) Change axis by 90 deg

Question 3

.Types of astigmatism (based on corneal topography)

Answer 3

1) Regular - When ref P along meridian is smooth AND principal meridians are perpendicular
2) Irregular - When variations in ref P along meridian OR principal meridians are not perpendicular

Question 4

.Shifts in astigmatism (Infant -> Adult)

Answer 4

1) Infant - ATR
2) Teenager - WTR
3) Older adult (> 40 yo) - ATR

Question 5

.Possible causes of irregular astigmatism

Answer 5

1) Corneal scarring
2) Refractive surgery
3) Cataract surgery

Question 6

.Clinical tests for astigmatism

Answer 6

1) JCC
2) Keratometry
3) Retinoscopy

Question 7

.Types of astigmatism (based on Rx)

Answer 7

1) Low (< or = 1.00)
2) Med (1.25-3.00)
3) High (> 3.00)

Question 8

.Apply short form of Javal’s rule, given keratometry results

Answer 8

ATR
Horiz P >
Correct w/ vert axis (within 30 deg of 90)

WTR
Vert P >
Correct w/ horiz axis (within 30 deg of 180)

Oblique
No change

Question 9

.Det actual Rx for patient w/ cyl taped behind phoropter

Answer 9

Subtract amount of cyl placed in OPP meridian