Keratometry

Question 1

which refractive errors does the keratometer measure in

Answer 1

the 2 prinicpal meridieans of the cornea

Question 2

the keratometer provides information about the ______ not the ______

Answer 2

astigmatism

not about the spherical ametropia

Question 3

what is another name for the keratometer

Answer 3

ophthalmometer

Question 4

it meausre the curvature of the central ___ to ___mm of the ______ surface of the cornea

Answer 4

3.5-3.75

anterior

Question 5

the keratometre is used to predict ______ after refraction

Answer 5

total astigmatism

Question 6

keratometer is used for ______ fitting and _____

Answer 6

CL fitting

follow-up

Question 7

the cornea acts as a ____ mirror and ______ refracting surface

Answer 7

convex

convex

Question 8

what eye movements hinder the measurement

Answer 8

nystagmoid

Question 9

what do you double the mires using

Answer 9

prism

Question 10

wollaston or biprism is used in ______ keratometers

-the drum is rotated for measurement in the ____meridian

Answer 10

2 position keratometers

-second

Question 11

B & L keratometer is used in _____ keratometers.

-uses 2 prisns oriented how?

Answer 11

one postion

verticaly &horiz

Question 12

what do the upper and lower apertures use to keep the mires in sharp focus

Answer 12

scheiner’s disk principle

Question 13

image is virtual and erect and smaller than the object

Answer 13

mires

Question 14

what is the relationship between mm and diopters

Answer 14

reciprocal

Question 15

what kind of radius does a steep cornea have

what kind of radius does a flat cornea have

Answer 15

short

long

Question 16

the average cornea is

Answer 16

43 to 44 D

Question 17

how much does the cornea flatten btwn birth and age 1

Answer 17

5-10 D

Question 18

what is the range of B&L keratometer

Answer 18

36-52D

Question 19

what can the range of the keratometer be extended using

Answer 19

spherical lenses

Question 20

more power in the vertical meridian is

Answer 20

with the rule

Question 21

more power in the horizontal meridian is

Answer 21

against the rule

Question 22

what is not w/in 30 degrees of 90 or 180

Answer 22

oblique

ex. 42.00/43.00 @055 1.00 oblique

Question 23

the two principal meridians are NOT 90 degrees apart

Answer 23

irregular

ex. 45.00@165/52.00@90 7.00irregualr

Question 24

empirically predicts total refractive astig from K readings

Answer 24

javal’s rule

Question 25

javal’s rule is….

Answer 25

total astig = 1.25 (corneal astig) + internal asig

internal astig = 0.50 AR

Question 26

javal’s rules works for ….

doesnt work for…

Answer 26

WR or AR

doesnt work w/ oblique and ireg

Question 27

what are some problems with javals rule

Answer 27

internal astig is variable and increases w/ age

• there may be sources of internal asig other than the lens
• the constant 1.25 is an approx. and doesn’t take ametropia into consideration

Question 28

if there is significant refractive astig, it probalby comes from….

Answer 28

the cornea

Question 29

if there is significant corneal astig, it will show up on…

Answer 29

the refraction

Question 30

K’s and refraction are…

Answer 30

highly correlated

Question 31

what is oblique astig at for axes

Answer 31

cyl x 30 to 60. and x120 to 150