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Optics II block 5 > Lenticular Optics > Flashcards

Lenticular Optics Flashcards

1
Q

The horizontal visible iris diameter, HVID

A

The horizontal corneal diameter

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2
Q

Vertical visible iris diameter (VVID)

A

Vertical corneal diameter

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3
Q

The anterior corneal curvature (ACC) relates to the ______ of the cornea

A

Shape of the front surface

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4
Q

Crystalline lens proved approximately ______ of the total static refractive power of the eye

A

1/3

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5
Q

What are the two purposes of the crystalline lens

A
  • combines with cornea to form image on the retina

- mechanism for focusing at different distances

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6
Q

What kind of optical elements is the crystalline lens

A

Active

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7
Q

Crystalline lens is ______ in form

A

Biconvex

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8
Q

What is the diameter of the crystalline lens

A

9mm

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9
Q

What is the thickness of the lens when it is relaxed

A

3.6mm

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10
Q

How much bigger is the anterior surface radius of the lens than the posterior

A

1.7 times

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11
Q

Cornea is what kind of optical element

A

Static

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12
Q

What are the fundamental building block of the lens

A

Many lens fiber cells arranged in a hexagonal pattern

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13
Q

What do lens fibers cells do

A

Interdigitate to form sutures that make the lens very strong, and the suture is continuous through entire lens thickness

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14
Q

Lens growth throughout life

A

Grows constantly with new cells forming at the equator, then elongating as ‘fibers’ that wrap around the peripheral surface of the lens

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15
Q

What happens when the anatomy of the lens changes

A

The optical properties do to

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16
Q

What happens when the lens fibers are too coarse? *20microns)

A

Act as a diffraction grating

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17
Q

Close packing of the lens does what

A

Reduces light scatter at cell boundaries

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18
Q

How much light does the lens absorb

A

Very little due to no pigment

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19
Q

Lack of nutrients in the lens means what

A

These cells are metabolically inactive.

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20
Q

Why is the lack of nutrients and the fact that it is metaboclicalyl inactive goof

A

It is conducive for transmitting light, but cell damage cannot be reversed (cataract)

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21
Q

Anterior surface power of the crystalline lens

A

+5.1

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22
Q

Posterior surface power of the crystalline lens

A

+8.5D

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23
Q

What is the total lenticular power and why is it particular

A

+13.3D, it should be 21.35D and the difference is due to the different refractive indices in the lens

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24
Q

Where is the RI largest in the lens

A

Canter (1.402)

25
Q

Where is the RI smallest in the lens

A

Edge (1.386)

26
Q

A lens with a varying RI is called

A

Gradient index lens (GRIN)

27
Q

What makes up for the +8D of optical power of the lens

A

The small 1.2% change in RI between 1.402 and 1.386

28
Q

Manufacturing of GRIN lenses

A

Very difficult to manufacture and therefore rare in commercial optics, however such lense are common in nature

29
Q

What would happen if we replace the gradient index of human eye lens with a single lens with the same thickness, radii of curvature and refractive index?

A

The refractive index of the lens should be higher than the maximum RI of the gradient lens

30
Q

What is the equibvalent refractive index for lens

A

1.42, want to choose higher

31
Q

How does the human crystalline lens generate refraction?

A
  • varying refractive indices

- varying its axial length

32
Q

Where does refraction occur at the lens

A

Both the anterior and posterior surfaces of the lens as well as within

33
Q

The combined refraction of all surfaces of the lens produces _____ (relaxed)

A

+21..35D

34
Q

At accommodate state, lens refraction is _____

A

31.85D

35
Q

Relaxed axial thickness of lens

A

3-6mm

36
Q

Accomodative axial thickness of lens

A

4mm

37
Q

The distance between the near and the far points on the lens

A

Accommodation range

38
Q

When is the lens focused on the far point

A

Relaxed

39
Q

When is the lens focused on the near point

A

Accommodative

40
Q

What is a normal near point

A

2.5cm

41
Q

The difference between the vergence of the far and near points

A

Amplitude of accommodation

42
Q

Calculate the amplitude of accommodation (AA) of an eye with a far point of 1.25m and a near point of 10cm

A

Since AA is the difference between the vergence of the far and near points

The vergence of the far point is 1/1.25=0.8D
The vergence of the near point is 1/0.10=10D
The difference is 0.8D-10D=9.2D

43
Q

What is the equation to calculate AA based on age

A

AA=15-1/4(age)

10 y/o
15-1/4(10)=12.5D

50 y/o
15-1/4(50)=2.5D

44
Q

______ of both UV and visible wavelengths decrease with increase in age

A

Transmittance

45
Q

Scattering of light in aging eye

A

Happens in both forward and backward direction, increases with age, after 40 y/o

46
Q

Lens axial thickness and age

A

Increases all through life at a rate of 13 microns per year. This increase in axial thickness of lens decreases the anterior chamber depth through out life

47
Q

Anterior chamber depth and aging lens

A

Decreases because the lens axial thickness is increasing and taking up the room

48
Q

Anterior radius of curvature (shape) of lens and age

A

Reduces with increase in age. This change is from 16mm at 8yrs to 8.3mm at 82yrs

49
Q

Posterior radius of curvature(shape) of lens and age

A

Reduces slightly with increase age. This change is from 8.3mm at 8yrs to 7.5mm at 82 yrs

50
Q

Equatorial diameter of the lens and age

A

Of the unaccommodated lens increases from 8.5mm to 9.5mm between the age 15-85

51
Q

All possible shape changes in the lens and age

A

Declines with age, as reflected in the decrease in AA with age

52
Q

Any disturbance in the optical homogeneity of the lens, i.e., local changes in the refractive index, including fluid filled pools and opaque spots that scatter light

A

Cataract

53
Q

Color of lens and age

A

Yellows

54
Q

What does the nucleus of lens do with age

A

Scatters and prefertinally absorbs more light

55
Q

Eye contains the natural crystalline lens

A

Phakic

56
Q

Eye is without the natural crystalline lens

A

Aphakic

57
Q

Eye contains an IOL

A

Pseudophakic

58
Q

Best solution for phakic people (no lens)

A
  1. specs
  2. CL
  3. IOL (BEST OPTION)

Optics II block 5 (11 decks)

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