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Optical Science 6 > Ocular Structures 2 > Flashcards

Ocular Structures 2 Flashcards

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1
Q

Whats the total optical power of eye?

A

60 Diopters

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2
Q

How much power does the lens have?

A

20 Diopters

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3
Q

What makes the epithelial layer transparent?

A
  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.
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4
Q

Edematous epithelial layer of cornea is caused by what?

A

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.

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5
Q

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

A

a reduction in the transparency of the layer

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6
Q

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

A

reflections potentially occurring at many depths.

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7
Q

What layer of cornea is 90% the thickness?

A

stroma

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8
Q

Each lamella of corneal stroma contains what?

A

many collagen fibrils, regularly spaced.

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9
Q

Regular spacing in stroma causes what?

A

transparency

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10
Q

Irregular spacing in stroma causes what?

A

opaqueness

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11
Q

How many lamella are in the corneal stroma?

A

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

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12
Q

Collagen fibrils

A

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

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13
Q

What condition causes irregular spacing in stroma?

A

edematous corneal stroma

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14
Q

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

A

negatively impacts the pumping action of the endothelium

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15
Q

2 conditions causing stroma transparency

A

small fibrils

regular spacing

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16
Q

Why do scars cause opacity on cornea?

A

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

17
Q

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

A

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

18
Q

direct light

A

Light rays that form image on the retina

19
Q

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

A

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

20
Q

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

A

infrared light (wavelengths above 1.1 microns)

21
Q

What amount of power does the cornea contribute?

A

2/3 power of eye

22
Q

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

A

d=thickness
r=curvature
n=refractive index

23
Q

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

A

curvature (has more effect than thickness) and thickness

24
Q

Diabetes will cause what parameter of the eye to change?

A

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

25
Q

Divergence has negative or positive power?

A

negative

26
Q

Convergence has negative or positive power?

A

positive

27
Q

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?

A

-0.2 Diopters

use reciprocal of distance: 1/5

28
Q

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

A

-4 Diopters?

29
Q

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

A

image vergence (L’)

30
Q

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

A

back vertex power

31
Q

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

A
  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
32
Q

Where is the AC?

A

b/w cornea and lens

33
Q

What is the AC filled with?

A

aqueous humour

98% water content

34
Q

refractive index of aqueous humour

A

1.336

35
Q

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

A

refractive index and depth

36
Q

How does depth affect total power of eye?

A

If depth increases, total optical power decreases!

*inverse relationship

37
Q

When does the AC depth decrease?

A

when we accommodate

*this is why we have more power

38
Q

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

A

0.64 D

39
Q

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

A

1.3 D

Optical Science 6 (13 decks)

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