Corneal Optics Flashcards Preview

Optics 5 > Corneal Optics > Flashcards

Flashcards in Corneal Optics Deck (40):
1

What is the corneal power and how much of the total power does it account for?

+42 diopters
-about 2/3 of the total power of the eye

2

What is the refractive index of the cornea?

1.377

3

Each corneal layer has its own refractive index, but which layer dominates it?

The stroma

4

What is the diameter of the cornea?

12mm

5

What is the corneal thickness?

O.5mm

6

Is the cornea a spherical surface?

Nope

7

What aberration is associated with spherical lenses?

Spherical aberration
-marginal rays focus at a different spot than the central rays

8

What does an aspheric lens do?

It makes the curvature flatter to nullify the spherical aberration

9

The cornea is regarded as what shape?

Conicoid (ellipsoidal)

10

The anterior corneal asphericity values are usually what? What does that indicate?

-usually negative
-the cornea flattens away from the vertex

11

What are the two significant things that come from the corneal flattening away from the vertex?

1. To reduce spherical aberration
2. To make it smooth and join with the globe of the eye

12

Normal eccentricity is what?

0.73

13

What are the three corneal optical properties that effect vision?

1. Corneal diameter
2. Anterior corneal curvature
3. Central corneal thickness

14

How is the corneal diameter measured?

Limbus to limbus

15

Accurate measurement of corneal diameter helps what three things?

1. To make sure contact lens diameter is sufficient to cover the entire cornea
2. To produce the right size anterior chamber IOLs
3. To diagnose diseases

16

What is the average horizontal diameter? Vertical?

Horizontal: 11mm
Vertical: 12mm

17

What does corneal diameter do with age? Why?

Decreases with age due to narrowing of the anterior chamber (glaucoma)

18

Males have slightly _____________ corneal diameter than females?

Slightly wider horizontal corneal diameter

19

Asian CD is ___________ than whites?

Asian CD is smaller

20

What is toricity?

Curvature is different in different meridians

21

Is the cornea symmetric in regards to curvature and asphericity?

Nah it's asymmetric

22

Corneal shape geometry leads to differences in what?

Differences in spherical aberration

23

If the corneal surface flattens, what will happen to the spherical aberration?

It will decrease

24

If the cornea becomes steeper, what will happen to the spherical aberrations?

They will increase

25

Are myopes or hyperopes flatter?

Hyperopes

26

Each alteration in curvature equal to 400th of a mm in radius corresponds to a variation in how many diopters?

0.25D

27

Corneal refractive surgery showed an increase in what?

Corneal asphericity

28

A cornea that is too curved is a condition called what?

Keratoconus

29

A cornea that is too flat leads to a condition called what?

Cornea plana

30

In an average cornea, which meridian has a smaller radius?

Vertical meridian has a smaller radius (steeper)

31

Corneal curvature does what with age?

Becomes steeper with age due to changes in elasticity of the cornea

32

Which gender has steeper corneal curvature?

Females

33

Is there a difference in the corneal curvature between races?

Nope

34

A thin corneal thickness leads to what?

Underestimation of IOP

35

A thick corneal thickness leads to what?

Overestimation of IOP

36

What happens to the corneal thickness with age?

-decrease thickness with age

37

What race has a thinner corneal thickness than the others?

African americans

38

For a conicoid surface, the radius of curvature at off-axis points depends on what two things?

1. The distance from the vertex
2. On the meridian at that point

39

Which surface has the most significance on the corneal curvature?

Anterior surface corneal curvature

40

The mean posterior vertex radius is what? With a mean asphericity of what?

5.8mm
-0.42