Lecture 2- Corneal Optics Flashcards

(32 cards)

1
Q

Cornea has a fixed ________

A

optical power

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2
Q

Cornea has about ____of the total power of the eye (Relaxed).

A

2/3

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3
Q

Corneal Power is calculated as

A

~42 D

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4
Q

Cornea has a refractive index of _______

refractive Index of _________dominates the other corneal layers

A

1.377

stroma

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5
Q

Corneal diameter of about ______ in size

A

12 mm

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6
Q

The central corneal thickness (CCT) is about ________

A

0.5mm

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7
Q

Aspherity:

the cornea is regarded as a ________and the _____ is ____________

A

conicoid

conicoid
ellipsoidal

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8
Q

The Anterior corneal asphericity (Q) values are usually ______ which indicates that cornea ___________the vertex.

A

negative

flattens
away from

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9
Q

The significance of the corneal flattening away from the vertex or center is:
2 things-

A
  1. To reduce spherical aberration. .

2. To make smooth join with the main globe of the eye

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10
Q

__________ is limbus to limbus, (the

white of the eye)

A

Corneal diameter

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11
Q

Accurate measurement of CD helps,
• To ensure contact lens diameter is________________________
• To produce _______________________
• To diagnose diseases such as __________________

A

sufficient
to maintain full coverage of the cornea.

right size anterior chamber IOLs.

microcornea,
megalocornea, relative microphthalmos,
and corneal dystrophies.

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12
Q

• Horizontal diameter of the cornea on average is _______ in infants and ________ in adults

A

10 mm

11 mm

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13
Q

Vertical diameter of the cornea on average is______ in infants and_____in adults.

A

11 mm

12 mm

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14
Q

Age: Studies show that corneal diameter (CD) _________ slightly with age due to:

A

decreases

the age related narrowing of anterior chamber increasing the chances of glaucoma.

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15
Q

• Gender: Males have significantly ______horizontal corneal diameter than their female
counterparts (in 130 eyes).

A

wider

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16
Q

Race: A study comparing corneal diameter of asian eyes (125) and Caucasian eyes (81)
shows that _______ CD is smaller than the _________. T

A

Asians

Caucasians

17
Q

Radius of curvature: Anterior corneal curvature (ACC) exhibit _______

18
Q

There are two principal meridians:
• the tangential meridian, which lies along
_____________and
• the sagittal meridian, which is______________

A

the radius line from the vertex,

perpendicular to the tangential meridian.

19
Q

Cornea is significantly _______ in both radius of curvature and asphericity

20
Q

If the refractive index, pupil diameter and asphericity are considered constant, the spherical
aberration will
• _______ if the corneal surface flattens and
• ________ as the cornea becomes steeper.

A

decrease

increase

21
Q

Hyperopes tend to be _______ than the myopic eyes (more –ve Q values for hyperopes than myopes).

22
Q

Cornea too curved leads to a condition called

___________.

23
Q

Cornea too flat leads to a condition called

_________

A

Cornea plana.

24
Q

The average cornea curvature has a smaller radius in the_______meridian
compared to the __________meridian, which contributes to the ‘with-the-rule
astigmatism’ in young adults.

A

vertical

horizontal

25
- “__________” astigmatism occurs when the vertical meridian of the cornea is steepest
With-the-rule
26
- “_____________” astigmatism occurs when the horizontal meridian of the cornea is steepest
Against-the-rule
27
_________ becomes steeper with increasing age due to the | changes in the elasticity of the cornea.
Corneal curvature
28
Gender: __________had significantly steeper average corneal curvature than ____________
females males
29
The central corneal thickness (CCT) is | about________
0.5mm.
30
Race: Studies show that _______________ have | thinner CCT than other races.
African Americans and other African descent
31
Age: Several studies report that reduction of CCT with age due to the decrease in '_________ with age
keratocytes
32
For a conicoid surface, the radius of curvature at off-axis points depends upon 2 things:
the distance from the vertex, | • on the meridian at that point.