Keratometry

Question 1

The cornea is the largest contributor to ocular ______.

The cornea is mainly attributed to anterior surface curvature.

Answer 1

optical power

Question 2

Astigmatism has a smaller curvature it has a 1.____ meridian. With a larger curvature, it has a _____ meridian.

Answer 2

1. flat

2. steep

Question 3

Radius of curvature, the larger the radius the _____ the curvature.

Answer 3

Smaller

Question 4

Emmetropic focal point is on the

Answer 4

retina

Question 5

Hyperopic focal point is located

Answer 5

behind the retina

Question 6

Myopic focal point is located _______

Answer 6

in front of the retina

Question 7

Sturm conoid is

Answer 7

The bundle of rays formed by an astigmatic optical system consisting of a primary focal line.

Question 8

What is with-the-rule astigmatism?

Answer 8

With-the-rule astigmatism means that the EYE is steeper in the vertical meridian (more plus).

Question 9

What is against-the-rule astigmatism?

Answer 9

Against-the-rule astigmatism – the horizontal meridian is steepest

Question 10

What is toric surface?

Answer 10

Different radius of curvature along two principle meridians. i.e. football shaped

Question 11

Convex mirror type of image, location, and magnification:

Answer 11

Smaller, erect, virtual

Question 12

The cornea as a mirror has a 1. ____ radius of curvature, 2._____ curvature, and a 3._____ sized image.

Answer 12

1. smaller radius
2. larger curvature
   3, even smaller image

Question 13

External Corneal Surface:

Answer 13

A Convex Mirror!

Question 14

We extrapolate to Corneal Optical power.

Answer 14

Astigmatism!

Question 15

From the image magnification we calculate curvature, and thus, indirectly, Optical Power of the anterior cornea. What meridian does this happen?

Answer 15

Can do so in any given meridian,

Question 16

What are the basic steps of keratometry?

Answer 16

1. Project an image on the cornea
2. Line Up
3. Compare magnifications
4. Measure Radius of Curvature

Question 17

KERATOMETRY LIMITATIONS

Primary data taken from four points on the center __mm

Answer 17

3 mm

Question 18

KERATOMETRY LIMITATIONS

Assumes a lot. Paraxial approximation only, ____ order aberrations only

Answer 18

low order aberrations only

Question 19

KERATOMETRY LIMITATIONS

Assumes ____ symmetric cornea (spherocylindrical)

Answer 19

rotationally symmetric cornea

Question 20

KERATOMETRY LIMITATIONS

Assumes some symmetry, such as corneal apex, _____ axis, and the axis of the instrument to coincide

Answer 20

visual axis

Question 21

KERATOMETRY LIMITATIONS

Assumes ‘normal’ astigmatism, i.e. the two main meridians are _____________.

Answer 21

perpendicular

Question 22

KERATOMETRY LIMITATIONS 
Corneal abnormalities (\_\_\_\_\_\_\_) may be rather challenging to measure

Answer 22

keratoconus

Question 23

KERATOMETRY LIMITATIONS

Cannot measure _______.

Answer 23

asphericity

ASPHERICITY is a measure of the shape of a. refractive medium and how it affects bending of. light. When light goes through an optical medium. or lens surface, the shape of the optical medium.

Question 24

KERATOMETRY LIMITATIONS

Tear film influences keratometry. How?

Answer 24

If the tear film is oily or disrupted, or the cornea has subtle dystrophy or degeneration, it will be reflected in the quality of the measurements (akin to the changes of a pebble tossed into a placid lake).

Question 25

What are benefits of topography?

Answer 25

1. It provides a multitude of data (such as contact lens fitting)
2. Applicable to any corneal abnormality
3. Curvature and optical power on any meridian we select. Not limited to just two.
4. Easy-to-use, requires just proper centration

Question 26

Normal mire spacing = _______
Sparser mire spacing = ______
Denser mire spacing = ______

Answer 26

1. Normal mire spacing = normal cornea
2. Sparser mire spacing = flatter cornea (larger magnification, reduced curvature)
3. Denser mire spacing = steeper cornea
   (smaller magnification, increased curvature)

Question 27

What is the keratometric equation?

Answer 27

R * P = 337.5 (keratometric equation)