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Block 5 > Optics: Crystalline Lens > Flashcards

Optics: Crystalline Lens Flashcards

1
Q

The crystalline lens provides approx. _____ of total static refractive power of the eye

A

1/3

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2
Q

What are the two purposes of the lens

A

-Combine with cornea to form image on the retina
-provides a mechanism for focusing at different distances

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3
Q

The Lens ______ in form, with a diameter of ____ mm

A

Biconvex, 9mm

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4
Q

For a relaxed lens, the thickness is ___mm.

A

3.6

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5
Q

The anterior surface radius of lens is about ___ times that of the posterior surface.

A

1.7

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6
Q

The lens is shaped like a ____ spheroid

A

Oblate

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7
Q

The lens consists of what three parts

A

Capsule, epithelium, and fiber cells

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8
Q

The lens capsule is..

A

A thin acellular membrane that envelops the lens

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9
Q

What role does the lens capsule play in accommodation

A

Distributes the force produced by normal zonular tension across the lens surface

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10
Q

The lens capsule is thicker at the ____ than the ____ lens capsule

A

Anterior, posterior

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11
Q

Does age increase or decrease the thickness of the lens?

A

INCREASE

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12
Q

Lens epithelium is located

A

Beneath the capsule in the anterior and equator

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13
Q

Lens epithelium is not present on which part of the lens

A

Posterior

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14
Q

Lens fiber cells are arranged in a ____ pattern

A

Hexagonal

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15
Q

Lens fibers cells ____ to form sutures that make the lens very strong

A

Interdigitate (picture dr. Martin interlocking his fingers)

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16
Q

The suture is ____ through entire lens thickness

A

Continuous

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17
Q

As the anatomy of the lens changes so does the _____ properties

A

Optical

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18
Q

The lens grows through out life with new cells forming at the

A

Equator, then elongating to peripheral

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19
Q

Lens fibers are too ____ to act as diffraction grating

A

Coarse

20
Q

The close packing of the fiber cells reduces ___ ____ at cell boundaries

A

Light scattering— lens absorbs little light(no pigment and a vascular)

21
Q

The lack of nutrients of the lens means that the cells are _________ inactive.

A

Metabolically

22
Q

Being metabolically inactive is conductive fro transmitting light but it also means that the lens cannot

A

Reverse cell damage e.g cataract

23
Q

Because the refractive index of the crystalline lens varies from center to edge, it is called

A

Gradient index lens or GRIN

24
Q

The missing 8 diopters for the lens to add up to about 21D is due to what?

A

The change in refractive index throughout the lens

25
Q

Are GRIN lenses commonly made commercially?

A

Nope, its very hard to make them but the lenses are common in nature

26
Q

If using the equivalent refractive index, it needs to be ___ compared with the maximum value of the gradient lens of about 1.406

A

1.42

27
Q

Refraction occurs at ______, ______, and _______ on the crystalline lens

A

Anterior, posterior, and within

28
Q

The combined refraction produces ____ D

A

21.35

29
Q

At accommodated state, lens refraction is ___ D.

A

31.85

30
Q

Does lens thickness increase with accommodation?

A

YES

31
Q

Does curvature increase with accommodation?

A

YEAH

32
Q

The distance between the far and near points is called

A

Accommodation range

33
Q

What is amplitude of accommodation

A

The difference between the vergence of the far and near points

34
Q

How can you estimate your AA using your age

A

15-(1/4)age

35
Q

Aging Eye: transmittance of UV and visible wavelengths

A

Decrease

36
Q

Aging Eye: scattering of light for both forward and backward direction

A

Increases, after 40years old

37
Q

Aging Eye: lens axial thickness

A

Increase at 13 microns per year

38
Q

Aging Eye: Lens axial thickness increases so ___ ____ depth decreases

A

Anterior chamber depth

39
Q

Aging Eye:anterior radius of curvature

A

Reduces
16mm @ 8yrs
8.3mm @ 82yrs

40
Q

Aging Eye: posterior radius of curvature

A

Reduces slightly

41
Q

Equatorial diameter of the unaccommodated lens

A

Increases

42
Q

All possible shape changes _____ in the lens as we age

A

Decrease

43
Q

A cataract is any disturbance in the optical ______ of the lens such as …

A

Homogeneity
Fluid filled pools and opaque spots that scatter light

44
Q

Phakic eye

A

Contains the natural lens

45
Q

Aphakic eye

A

Is without the natural lens

46
Q

Pseudophakic eye

A

Contains an intraocular lens

47
Q

What are the three options for aphakic eyes? Which is most common?

A

1.spectacles
2.contact lens
3. Intraocular lenses(best and most common)

Block 5 (13 decks)

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