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Optics 5 > Lenticular Optics > Flashcards

Lenticular Optics Flashcards

1
Q

The lens makes up how much of the total power of the eye?

A

1/3

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2
Q

What are the two purposes of the lens?

A
  1. It combines with the cornea to form an image on the retina
  2. It provides a mechanism for focusing at different distances
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3
Q

What form is the lens in and what is the average diameter?

A

Biconvex form

9mm

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4
Q

The anterior surface of the lens is how much larger than the posterior surface?

A

1.7 times larger

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5
Q

The lens fiber cells are arranged in what kind of shape?

A

Hexagonal shape

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6
Q

Do the lens fibers act as diffraction grating?

A

Nope

The fibers are too course

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7
Q

What prevents the scattering of light on the lens?

A

The close packing of the cells

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8
Q

Does the lens have a pigment? Does it have nutrients? What do those answers indicate about the lens?

A
  • no pigment means no absorption
  • no nutrients means they are metabolically inactive so although it is good for transmitting light, cell damage cannot be reversed
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9
Q

What physical change happens with the lens in presbyopia?

A

Pigmentation of the lens

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10
Q

What accounts for the 8 diopter difference between what we calculated for lens power(13) and the actual power (21)?

A
  • the refractive index of the lens radially varies, making it a gradient index lens
  • changing the refractive index from 1.386 to 1.402 makes up the difference
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11
Q

Where is the index of refraction largest in the lens? Smallest?

A

Largest- 1.402 at the nucleus

Smallest- 1.386 at the poles

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12
Q

What kind of lens has a varying refractive index?

A

Gradient index lens

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13
Q

If we wanted to replace the lens of the human eye with a single lens, what would it need to have?

A

The lens would need to have an index of refraction higher than the maximum refractive index of the gradient lens we are replacing (1.42 instead of 1.406)

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14
Q

What are the two ways the lens generates refraction?

A
  1. Varying refractive indices

2. Varying axial thickness

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15
Q

What surface of the lens does refraction occur?

A

On both the anterior and posterior surfaces of the lens AND within

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16
Q

What is the power refraction of the lens generates in a relaxed state? In accommodation?

A
  1. 35 at relaxed

31. 85 in accommodation

17
Q

Is the axial thickness of the lens larger or smaller in an accommodative state?

A

3.6mm in relaxed state and 4mm in accommodation state

Larger thickness in accommodation

18
Q

Does the center of curvature remain the same in different states?

A

Nope

19
Q

What is the accommodation range?

A

The DISTANE between the far and near points

20
Q

What point are you seeing in relaxed state? Accommodation?

A

Relaxed-far point

Accommodation- near

21
Q

What happens to the near point as we age? What kind of eye experiences this faster!

A

The near point gets further and further away

- hyperopes experience this change faster

22
Q

What is the amplitude of accommodation?

A

The difference between VERGENCES of the far and near points

23
Q

What is the equation for amplitude of accommodation?

A

15- 1/4 of your age

24
Q

What happens to transmittance of the lens as we age?

A

Transmission of UV and visible light decrease with age

25
Q

What happens to scattering as we age?

A

Forward and backward scattering both increase after 40.

26
Q

How much does the lens thickness increase per year?

A

13 microns per year

27
Q

What does the increase in lens thickness do to the anterior chamber?

A

It decreases the anterior chamber depth

28
Q

What does the anterior radius of curvature do as you age? Specific numbers please

A
  • it decreases significantly as you age

- goes from 16 to 8.3

29
Q

What does the equatorial diameter of the unaccommodated lens do with age?

A

It increases

30
Q

All possible shape changes in the lens decline with age which is reflected in what?

A

The decrease in amplitude of accommodation

31
Q

Morphological, what is a cataract?

A
  • any disturbance in the optical homogeneity of the lens
  • local changes in the refractive index
  • includes fluid-filled pools and opaque spots that scatter light
32
Q

As you age, is there more of less scattering? More or less absorption?

A

-nucleus scatters more and absorbs light more

33
Q

What is a phakic eye?

A

It contains the natural crystalline lens

34
Q

What is an aphakic eye?

A

An eye without the natural crystalline lens

35
Q

What is a pseudophakic eye?

A

An eye that contains an IOL

36
Q

Why are spectacles usually not used to replace the crystalline lens?

A

The high power creates a distorted image and a 25% magnification

37
Q

Contact lenses replacing the lens cause what amount of magnification?

A

7% (less than spectacles)

38
Q

What is the best and most common solution for replacing a crystalline lens?

A
  • IOLs
  • minimal magnification
  • normal peripheral vision

Optics 5 (4 decks)

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