Ocular Structures 2

Question 1

Whats the total optical power of eye?

Answer 1

60 Diopters

Question 2

How much power does the lens have?

Answer 2

20 Diopters

Question 3

What makes the epithelial layer transparent?

Answer 3

1. Cells have a homogeneous refractive index.
2. Cells are void of opacities and pigments that absorb light.
3. Cells are packed tightly together with no extracellular fluid in between.

Question 4

Edematous epithelial layer of cornea is caused by what?

Answer 4

This condition can be caused by too much exposure to ultraviolet radiation. It is considered a type of “sunburn”, albeit of the cornea rather than the skin.

Question 5

The difference in refractive index between the fluid and cells redirects some of the incident light causing ?

Answer 5

a reduction in the transparency of the layer

Question 6

Edema can reside throughout the entire thickness of the corneal epithelial layer with….

Answer 6

reflections potentially occurring at many depths.

Question 7

What layer of cornea is 90% the thickness?

Answer 7

stroma

Question 8

Each lamella of corneal stroma contains what?

Answer 8

many collagen fibrils, regularly spaced.

Question 9

Regular spacing in stroma causes what?

Answer 9

transparency

Question 10

Irregular spacing in stroma causes what?

Answer 10

opaqueness

Question 11

How many lamella are in the corneal stroma?

Answer 11

~200 Lamella, limbus to limbus 1 to 2μm each

Question 12

Collagen fibrils

Answer 12

dia=30 nm (about 1/17 of wavelength)
spacing=64 nm (about 1/8 wavelength)
n fibrils= 1.55 fibrils
n spacing= 1.35

Question 13

What condition causes irregular spacing in stroma?

Answer 13

edematous corneal stroma

Question 14

If there is a tear in descemet’s membrane what will happen?

Answer 14

negatively impacts the pumping action of the endothelium

Question 15

2 conditions causing stroma transparency

Answer 15

small fibrils

regular spacing

Question 16

Why do scars cause opacity on cornea?

Answer 16

New collagen fibrils are generally much larger in diameter (e.g., 5 times) and arranged in a random pattern.

Question 17

Why is the sclera opaque, while cornea is transparent even tho both consist of collagen fibers?

Answer 17

collagen fibrils in the sclera form irregular bundles and are much thicker

Question 18

direct light

Answer 18

Light rays that form image on the retina

Question 19

Why are there no blood vessels in Cornea, Lens or Vitreous?

Answer 19

blood is not transparent like water, we wouldn’t want it in our eye because it will degrade the retinal image

Question 20

Water is highly transparent in visible light, but highly absorbent in what type of light?

Answer 20

infrared light (wavelengths above 1.1 microns)

Question 21

What amount of power does the cornea contribute?

Answer 21

2/3 power of eye

Question 22

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

Answer 22

d=thickness
r=curvature
n=refractive index

Question 23

Refractive Surgery will cause what parameter of the eye to change?

Answer 23

curvature (has more effect than thickness) and thickness

Question 24

Diabetes will cause what parameter of the eye to change?

Answer 24

refractive index (glucose levels will change aqueous and vitreous); power changes b/c refractive index changes

Question 25

Divergence has negative or positive power?

Answer 25

negative

Question 26

Convergence has negative or positive power?

Answer 26

positive

Question 27

If your TV is 5 meters away from your eye, and you have no refractive error what vergence does the TV have to your eye?

Answer 27

-0.2 Diopters | use reciprocal of distance: 1/5

Question 28

If patient is a -3 Diopter without correction and TV is 1 M away, how much correction is needed to view TV clearly?

Answer 28

-4 Diopters?

Question 29

object vergence (L) + surface power (F)=

Answer 29

image vergence (L')

Question 30

When using a keratometer, what type of power are we reading?

Answer 30

back vertex power

Question 31

Methods for measuring axial distances within the optics of the eye.

Answer 31

1. Simple optical pachometer (not clinically viable) 2. Optical pachometry using a slit lamp biomicroscope 3. Orbscan (computer-controlled slit lamp) 4. Ultrasonic pachometry 5. Optical coherence tomography

Question 32

Where is the AC?

Answer 32

b/w cornea and lens

Question 33

What is the AC filled with?

Answer 33

aqueous humour | 98% water content

Question 34

refractive index of aqueous humour

Answer 34

1.336

Question 35

What are the 2 key properties of AC that affect the optical power of the eye?

Answer 35

refractive index and depth

Question 36

How does depth affect total power of eye?

Answer 36

If depth increases, total optical power decreases! | *inverse relationship

Question 37

When does the AC depth decrease?

Answer 37

when we accommodate | *this is why we have more power

Question 38

1 mm change in depth produces how much total optical power of the eye?

Answer 38

0.64 D

Question 39

1 mm change in depth produces how much refractive error of the eye?

Answer 39

1.3 D