Lecture 1

Question 1

Which surface in the eye has the most power?

Answer 1

Tear film.

Question 2

How thick is the tear film

Answer 2

10 microns

Question 3

What finger like projections extend into the tear film and what is its size?

Answer 3

Microvilli and 1/2 microns

Question 4

What is the main role of the tear film?

Answer 4

Smooth the rough surface created by the microvilli

Question 5

Which interface has the worst index match?

Answer 5

Air to Tear

2.3%

Question 6

Which interface has the best index match?

Answer 6

Tear to Cornea

0.0048%

Question 7

What is the reflectance and transmittance of the air/tear interface

Answer 7

R= 2.29%
T= 97.71%

Question 8

What is the reflectance and transmittance of the tear/cornea interface?

Answer 8

R=0.005%

T=99.995%

Question 9

Assuming no light scattering in the tear layer, what percent of the incident light makes it into the cornea?

Answer 9

97.70%

Question 10

What are the 2 methods of clinically assess the tear film intergrity?

Answer 10

1) Retroillumination of pupil with slit lamp

2) Fluorescein

Question 11

What is the TBUT for males, females and CL wearers?

Answer 11

Males = 18 sec
Females = less than 18 sec
CL = Greater than 10 secs

Question 12

How much does the cornea cover of the outer tunic of the eye?

Answer 12

1/6th

Question 13

What is the diameter of the eye?

Answer 13

11-13mm

Question 14

What part of the cornea is flatter and thicker?

Answer 14

Peripheral part

Question 15

What is the refractive power of the cornea?

Answer 15

about 40 D

Question 16

What does the Stroma mostly consist of?

Answer 16

90% collagen lamellae

Question 17

Which region of the cornea will show a horizontal strip?

Answer 17

Stroma

Question 18

What is the absorbant number for blood?

Answer 18

0.6um

Question 19

What is the wavelength that is absorber by infared light?

Answer 19

1.1 - 2.5um

Question 20

What parameters of the eye influence the power of the cornea?

Answer 20

Radius and Thickness

Question 21

What are the values of these for your eye?

What clinical implications do these have?

Answer 21

7.7mm for the anterior and 6.8mm in the posterior.

Implications - Refractive surgery (changes curvature) and thickness

Question 22

What is the back vertex power of the cornea when immersed in water?

How does the new power compare to that in air?

Is the eye hyperopic or myopic?

What is the back vertex power of the reduced eye when immersed in water?

Answer 22

• 5.88 + 5.59 = -0.29
  43. 93 - (-0.29) = 44.12D

Hyperopic

OD

Question 23

a) What is the back-vertex
power of the cornea when
refractive surgery is used to increase the radius of curvature of the anterior surface by 0.3 mm?

b) b) How do the pre- and post-surgical powers of the cornea compare?

Answer 23

a) The curvature will become 8 mm.
ANS: -5.88D + 47.82D = 41.9D

b) ANS: 43.83D -41.9D = 1.93D
Ie. The post surgical power is 1.93D less

Question 24

What are the clinical implication of corneal thickness?

Answer 24

Due to the fact if someone has a thicker CT, F2 of the back vertex would increase aswell.

Question 25

True of False. Image of the posterior cornea is located closer to the anterior cornea and is magnified?

Answer 25

True Note: Objects behind the cornea are farther than they appear.

Question 26

What is the formula for anterior chamber depth?

Answer 26

d = n/L'

Question 27

What is the actual corneal thickness?

Answer 27

0.5mm

Question 28

What is the thickness formula?

Answer 28

Velocity x Time/2

Question 29

What are the 4 fundamental properties of light?

Answer 29

``` CWIP Coherence Wavelength Intensity Polarization ```

Question 30

What type of properties are used for Interferometer?

Answer 30

Coherence Note: 10 Microns and less is what type of tissue that can be measured

Question 31

What is the amount of water in the Aqueous humour?

Answer 31

98%

Question 32

Does the anterior chamber have any optical significance?

Answer 32

Refractive index and depth are the two key properties of the anterior chamber that affect the optical power of the eye

Question 33

The human visual system operates over a 10-log range. How much does the changing pupil size contribute to this?

Answer 33

16x in luminance, 1.2 log but is small compared to the entire visual system

Question 34

What happens to the depth of field when the pupil is increased?

Answer 34

Decreases

Question 35

What is the formula for depth of field?

Answer 35

Depth of Field = 2/pupil diameter

Question 36

What type of slit, small or large, generate noticeable deviations?

Answer 36

Small