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Optics 5 > Corneal Optics > Flashcards

Corneal Optics Flashcards

1
Q

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

A

+42 diopters

-about 2/3 of the total power of the eye

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2
Q

What is the refractive index of the cornea?

A

1.377

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3
Q

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

A

The stroma

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4
Q

What is the diameter of the cornea?

A

12mm

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5
Q

What is the corneal thickness?

A

O.5mm

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6
Q

Is the cornea a spherical surface?

A

Nope

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7
Q

What aberration is associated with spherical lenses?

A

Spherical aberration

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

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8
Q

What does an aspheric lens do?

A

It makes the curvature flatter to nullify the spherical aberration

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9
Q

The cornea is regarded as what shape?

A

Conicoid (ellipsoidal)

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10
Q

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

A
  • usually negative

- the cornea flattens away from the vertex

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11
Q

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

A
  1. To reduce spherical aberration

2. To make it smooth and join with the globe of the eye

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12
Q

Normal eccentricity is what?

A

0.73

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13
Q

What are the three corneal optical properties that effect vision?

A
  1. Corneal diameter
  2. Anterior corneal curvature
  3. Central corneal thickness
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14
Q

How is the corneal diameter measured?

A

Limbus to limbus

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15
Q

Accurate measurement of corneal diameter helps what three things?

A
  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
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16
Q

What is the average horizontal diameter? Vertical?

A

Horizontal: 11mm
Vertical: 12mm

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17
Q

What does corneal diameter do with age? Why?

A

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

18
Q

Males have slightly _____________ corneal diameter than females?

A

Slightly wider horizontal corneal diameter

19
Q

Asian CD is ___________ than whites?

A

Asian CD is smaller

20
Q

What is toricity?

A

Curvature is different in different meridians

21
Q

Is the cornea symmetric in regards to curvature and asphericity?

A

Nah it’s asymmetric

22
Q

Corneal shape geometry leads to differences in what?

A

Differences in spherical aberration

23
Q

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

A

It will decrease

24
Q

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

A

They will increase

25
Q

Are myopes or hyperopes flatter?

A

Hyperopes

26
Q

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

A

0.25D

27
Q

Corneal refractive surgery showed an increase in what?

A

Corneal asphericity

28
Q

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

A

Keratoconus

29
Q

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

A

Cornea plana

30
Q

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

A

Vertical meridian has a smaller radius (steeper)

31
Q

Corneal curvature does what with age?

A

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

32
Q

Which gender has steeper corneal curvature?

A

Females

33
Q

Is there a difference in the corneal curvature between races?

A

Nope

34
Q

A thin corneal thickness leads to what?

A

Underestimation of IOP

35
Q

A thick corneal thickness leads to what?

A

Overestimation of IOP

36
Q

What happens to the corneal thickness with age?

A

-decrease thickness with age

37
Q

What race has a thinner corneal thickness than the others?

A

African americans

38
Q

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

A
  1. The distance from the vertex

2. On the meridian at that point

39
Q

Which surface has the most significance on the corneal curvature?

A

Anterior surface corneal curvature

40
Q

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

A
  1. 8mm

- 0.42

Optics 5 (4 decks)

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