Topography

Question 1

What is a typically cornea radius of curvature

Answer 1

7.5mm

Question 2

Is 8.6 a flat or steep radius of curvature for cornea

Answer 2

Flat

Question 3

Does a flat corean have more or less power

Answer 3

Less

Question 4

Does a steep cornea have more or less power

Answer 4

More

Question 5

An approximate relationship for the calculation of optica power of the cornea by considering one surface, the anterior

Answer 5

Keratometric equation

Question 6

What do we need to accurately measure total corneal power

Answer 6

Anteiror corneal curvature, posterior corneal curvature, and CCT

Question 7

Corneal curvature and optical power

Answer 7

P=n’-n/R

Question 8

What does keratometry measure

Answer 8

Only measures the front surface

Make assumptions that the back surface looks exactly like the anterior surface

Question 9

Large curvature means a _______ radius of curvature

Answer 9

Small

Question 10

What is the image on the corneal surface

Answer 10

Upright
Minified
Virtual

Question 11

Focal distance

Answer 11

F=R/2

Question 12

What does the keratometry actually measure

Answer 12

The tear film

Question 13

Keratometry limitation

Answer 13

• Only works in center
• Normal cornea
• significant assumptions
• assumes rotational symmetry
• assumes some symmetry
• assumes normal astig
• corneal abnormalities may be challenging
• cannot measure aspherity
• tear film may limit the measurement accuracy

Question 14

Mires: flatter at the center steeper at the periphery

Answer 14

Non-equidistant mires

Question 15

Denser mire spacing

Answer 15

Steeper cornea

Question 16

Sparser mire spacing

Answer 16

Flatter cornea

Question 17

Mires: WTR astigmatism

Answer 17

Oblong like a football lying down

Question 18

Mires: ATR astigmatism

Answer 18

Oblong like football standing on end

Question 19

Mires: flatter at the center and the periphery

Answer 19

Asphericity

Question 20

Keratoconus mires

Answer 20

Steeper in the bottom, flatter in the top

Question 21

Denser mires

Answer 21

Smaller magnification
Increased curvature
More power

Question 22

Sparser mirers

Answer 22

Larger magnification
Reduced curvature
Less power

Question 23

Things about topography

Answer 23

• provides multitude of other data such as CL fitting
• applicable to ant corneal abnormality
• curvature and optical power on any meridian we select. Not limited to just two
• easy-to-use, requires just proper centration

Question 24

Keratometry

Answer 24

• measurements only at central 3mm
• curvature and optical power only for 2 meridians
• manual alignment

Question 25

If given the power of the power of the cornea (42.2D), how do you find the radius of curvature?

Answer 25

337.5/42.2=8mm

Question 26

Is there more or less power in the periphery of the cornea?

Answer 26

Less power, because its steeper

Question 27

Simulated keratometry

Answer 27

Simulated, not real

Based on keratometric assumptions