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