Lecture 6 - Keratometry

Question 1

How much curvature of the cornea accounts of the eye’s refracting power?

Answer 1

2/3

Question 2

What formula do you use to convert from diopters to a radius of curvature?

Answer 2

D = (n’ - n) / r

Note: 7.50 = 45D

Question 3

What shape if the cornea?

Answer 3

Prolate ellipsoid

Question 4

When do you add +1.25D trial lens over the keratometer (closest to the pt.)?

Answer 4

When the cornea is too steep.

Note: Once you get that number, multiply by 1.1659

Question 5

What type of lens do you tape over the keratometer when the cornea is too flat?

Answer 5

-1.00.

Note: then multiply by 0.8576

Question 6

If you have a pt. with K’s around 48 D, what finding could that mean?

Answer 6

Pt. is most likely a myopic

Question 7

What K’s reading would be adequate for a hyperopic pt?

Answer 7

40D

Question 8

In regards to Javal’s rule, the avg. pt. will have how many Diopters of ATR?

Answer 8

0.50 D

Question 9

What is the simplified formula for Javal’s rule?

Answer 9

Refractive Astigmatism = (keratometric astigmatism) + (+0.50 x 180)

Question 10

OD has -1.75D X 180 corneal astigmatism. What would be the predicted refractive astigmatism?

Answer 10

-1.25

Question 11

OD has -2.50D X 090 corneal astigmatism. What would be the predicted refractive astigmatism?

Answer 11

-3.00