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 is ______ 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

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
Are GRIN lenses commonly made commercially?
Nope, its very hard to make them but the lenses are common in nature
26
If using the equivalent refractive index, it needs to be ___ compared with the maximum value of the gradient lens of about 1.406
1.42
27
Refraction occurs at ______, ______, and _______ on the crystalline lens
Anterior, posterior, and within
28
The combined refraction produces ____ D
21.35
29
At accommodated state, lens refraction is ___ D.
31.85
30
Does lens thickness increase with accommodation?
YES
31
Does curvature increase with accommodation?
YEAH
32
The distance between the far and near points is called
Accommodation range
33
What is amplitude of accommodation
The difference between the vergence of the far and near points
34
How can you estimate your AA using your age
15-(1/4)age
35
Aging Eye: transmittance of UV and visible wavelengths
Decrease
36
Aging Eye: scattering of light for both forward and backward direction
Increases, after 40years old
37
Aging Eye: lens axial thickness
Increase at 13 microns per year
38
Aging Eye: Lens axial thickness increases so ___ ____ depth decreases
Anterior chamber depth
39
Aging Eye:anterior radius of curvature
Reduces 16mm @ 8yrs 8.3mm @ 82yrs
40
Aging Eye: posterior radius of curvature
Reduces slightly
41
Equatorial diameter of the unaccommodated lens
Increases
42
All possible shape changes _____ in the lens as we age
Decrease
43
A cataract is any disturbance in the optical ______ of the lens such as …
Homogeneity Fluid filled pools and opaque spots that scatter light
44
Phakic eye
Contains the natural lens
45
Aphakic eye
Is without the natural lens
46
Pseudophakic eye
Contains an intraocular lens
47
What are the three options for aphakic eyes? Which is most common?
1.spectacles 2.contact lens 3. Intraocular lenses(best and most common)