Lecture 2- Corneal Optics

Question 1

Cornea has a fixed ________

Answer 1

optical power

Question 2

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

Answer 2

2/3

Question 3

Corneal Power is calculated as

Answer 3

~42 D

Question 4

Cornea has a refractive index of _______

refractive Index of _________dominates the other corneal layers

Answer 4

1.377

stroma

Question 5

Corneal diameter of about ______ in size

Answer 5

12 mm

Question 6

The central corneal thickness (CCT) is about ________

Answer 6

0.5mm

Question 7

Aspherity:

the cornea is regarded as a ________and the _____ is ____________

Answer 7

conicoid

conicoid
ellipsoidal

Question 8

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

Answer 8

negative

flattens
away from

Question 9

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

Answer 9

1. To reduce spherical aberration. .

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

Question 10

__________ is limbus to limbus, (the

white of the eye)

Answer 10

Corneal diameter

Question 11

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

Answer 11

sufficient
to maintain full coverage of the cornea.

right size anterior chamber IOLs.

microcornea,
megalocornea, relative microphthalmos,
and corneal dystrophies.

Question 12

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

Answer 12

10 mm

11 mm

Question 13

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

Answer 13

11 mm

12 mm

Question 14

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

Answer 14

decreases

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

Question 15

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

Answer 15

wider

Question 16

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

Answer 16

Asians

Caucasians

Question 17

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

Answer 17

toricity.

Question 18

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

Answer 18

the radius line from the vertex,

perpendicular to the tangential meridian.

Question 19

Cornea is significantly _______ in both radius of curvature and asphericity

Answer 19

asymmetric

Question 20

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.

Answer 20

decrease

increase

Question 21

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

Answer 21

flatter

Question 22

Cornea too curved leads to a condition called

___________.

Answer 22

Keratoconus

Question 23

Cornea too flat leads to a condition called

_________

Answer 23

Cornea plana.

Question 24

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.

Answer 24

vertical

horizontal

Question 25

• “__________” astigmatism occurs when the vertical meridian of the cornea is steepest

Answer 25

With-the-rule

Question 26

• “_____________” astigmatism occurs when the horizontal meridian of the cornea is steepest

Answer 26

Against-the-rule

Question 27

_________ becomes steeper with increasing age due to the

changes in the elasticity of the cornea.

Answer 27

Corneal curvature

Question 28

Gender: __________had significantly steeper average corneal curvature than
____________

Answer 28

females

males

Question 29

The central corneal thickness (CCT) is

about________

Answer 29

0.5mm.

Question 30

Race: Studies show that _______________ have

thinner CCT than other races.

Answer 30

African Americans and other African descent

Question 31

Age: Several studies report that reduction of CCT with age due to the decrease
in ‘_________ with age

Answer 31

keratocytes

Question 32

For a conicoid surface, the radius of
curvature at off-axis points depends
upon 2 things:

Answer 32

the distance from the vertex,

• on the meridian at that point.