Lecture 6 & 7- Ret through a Manual Phoropter

Question 1

The ret. result needed with a minus cylinder phoropter before cylinder can be introduced in: ____ in one meridian and ____ in the second meridian

Answer 1

neutral; against

Question 2

____ measures the curvature of the central ____ cornea in about the center 3 mm of the cornea and determines its contribution to the total refractive power. Curvature of the cornea accounts for ___ ___ of the eyes refracting power

Answer 2

Keratometry; anterior; two thirds

Question 3

what is keratometry useful for

Answer 3

1. used in the fitting of contacts to determine the base curve needed on the back of the contact lens
2. useful for identifying patients with keratoconus
3. useful for determining the quality of the tear film and the integrity of the anterior central corneal surface.

Question 4

data on the keratometer is usually expressed in ____ even though the instrument does not actually measure refractive power. It really measures the _____ of curvature for a small portion of the central cornea

Answer 4

diopters; radius of curvature

Question 5

On the keratometer. The first line after the big line would be .12, then .25, then ____, then. .50, ___, .75 and lastly _____You want to get down to the nearest eighth.

Answer 5

.37; .62; .87

Question 6

The steeper the radius of curvature, the diopter value ______, the flatter the radius of curvature, the D value ____

Answer 6

increases; decreases

Question 7

the corneal refractive index is 1.376 but we use _____

Answer 7

1.3375

Question 8

the keratometer provides both quantitative and ____ data

Answer 8

qualitiative

Question 9

what shape is the cornea?

Answer 9

prolate (flattening)ellipsoid; the true apical radius is slightly steeper than the measured value; about 0.25 D steeper.

Question 10

the normal range of measurement for a keratometer is from ____ to ____. In keratoconus, the cornea is often steeper than 52.00

Answer 10

36.00; 52.00

Question 11

If cornea is too steep, extend the range of the keratometer by taping a _____ trial lends over the keratometer and afterwards multiply the diopteric reading by ____

Answer 11

+1.25; 1.1659

Question 12

If the cornea is too flat, tape a ____trial lens over the keratometer and measure the corneal curvature and multiply the reading by _____

Answer 12

0.8576

Question 13

for a contact lens fitting, normal K’s are _____. Patients with K’s of 48.00 more likely have ____. Patients with K’s of 40.00 most likely have _____.

Answer 13

44.00; myopia; hyperopia

Question 14

what is the use of keratometer data

Answer 14

1. determining the amount of corneal astigmatism
2. determining the refractive astigmatism.
3. javal’s rule

Question 15

In WTR astigmatism, the ____ principal meridian is horizontal. In ATR astigmatism, the flatter principal meridian is ___

Answer 15

flatter; vertical

Question 16

in oblique astigmatism, the flatter principal meridian is +/- ____ degrees of the 045 or 135 meridians

Answer 16

15

Question 17

Javal’s rule is useful when a patient has high astigmatism and is difficult to refract. It allows an estimate of both the ___ axis and ____ based upon the keratometry data. The avg patient has ____ D of against the rule astigmatism inside the lens of eye.

Answer 17

cylinder; power; 0.50

Question 18

For Javals rule when we have WTR astigmatism, we would ____0.50 for the internal ATR astigmatism. For ATR astigmatism, we would ____ 0.50

Answer 18

subtract; add

Question 19

If vertical meridian is steeper, it has a _____ radius of curvature

Answer 19

shorter

Question 20

If the corneas have similar K’s, the aniso is secondary to ____ length

Answer 20

axial

Question 21

If the corneas have different K’s, the aniso is secondary to a _____ etiology

Answer 21

refractive