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Optics II block 5 > Intraocular Lens > Flashcards

Intraocular Lens Flashcards

1
Q

Surgical solution for vision loss due to cataract formation

A

Vision correction with cataract surgery (monofocal IOL)

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2
Q

What can you achieve with a monfocal IOL

A 
20/20 vision at distance 
Image quality (or resolution efficiency)
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3
Q

Continuous vision for presbyopia

A
  • higher spectacle independence (far, inner, near correction)
  • continuous vision (bifocal,trifocals, EDF, monovision)
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4
Q

What are the different kinds of IOLs

A
  • surgical solution for vision loss due to cataract formation
  • continuous vision solution for presbyopia
  • accommodating vision or similar to nature crystalline lens
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5
Q

When does a spherical lens work

A

Smaller apertures

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6
Q

What happens with a larger aperture and a spherical lens

A

Generates higher spherical aberrations, which in turn affects the image quality

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7
Q

Why is an aspherical lens better

A

Provides higher image quality with minimal SA

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8
Q

What does the MTF of perfect lenses do with increasing refractive power

A

Increases at a certain spatial frequency

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9
Q

What does the MTF of lenses with aberration do with increasing refractive power

A

The modulation (or resolution) decreases with increasing refractive power above a certain limit

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10
Q

Symmetrical IOLs with RI of 1.46 and a 3.0mm aperture show what on MTF?

A

Perfect modulation up to about +15.0D

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11
Q

For power up to +25.0D, the modulation remains constant, and for powers above +25.0D…

A

There is a significant loss of modulation (contrast)

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12
Q

Increased curvature of IOL

A

Increased power, increased aberrations

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13
Q

What is the ISO standard for MTF of IOL?

A

About 0.4

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14
Q

Monofocal IOL

A
  • distant vision correction
  • non accommodative lens
  • very high image quality
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15
Q

What kind of IOL has very high image quality

A

Monofocal IOL

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16
Q

What is the equation for determining the power of the IOL needed in an eye

A

F(IOL)=A-2.5xAxial Length-0.9xK reading

A is a constant that reflects what the manufacturers have learned about the IOL position

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17
Q

Find the correct power for an IOL for someone with axial length 23mm, K reading of 43.5D, and A=118.2

A

F(IOL)=(118.2)-2.5(23)-0.9(43.5)

+21.6D

18
Q

Why is axial length so important in determine the power of the IOL?

A

If you are off by just 1mm, will be off by 2.5D, which is a very big difference

19
Q

What is the minimum resolution of an IOL for ISO standards

A

60

20
Q

IOLs and spec independence

A

In spite of high image quality achieved with monofocal IOLs, it only provides correction for distance vision and doesn’t provide ‘spectacle independence’

21
Q

What kind of IOL provides distant and near vision

A

Bifocal IOL

22
Q

What kind of optics does a bifocal IOL use

A

Refractive fresnel optics

23
Q

What gives the add power in a biofical IOL

A

Fresnel

24
Q

What gives the base power of a biofocal IOL

A

The monofocal part of the lens

25
Q

Alcon reSTOR diffractive IOL

A
  • diffractive design on central zone (3.6mm) refractive design on the peripheral zone
  • energy is divided equally between far and near
  • under mesopic or scoptopic condition, bifocals act as monfocal IOL because pupil gets larger and there is not sufficient energy for diffractive zones (fresnel structure doesn’t work)
26
Q

How good is the near vision in a bifocal IOL?

A

Never will reach 20/20

27
Q

Provides distant, intermediate, and near vision correction

A

Trifocals IOL

28
Q

ISO requirements for trifocals (multifocal)

A

They differ than that of monofocal

29
Q

At what cost do multifocal IOLs pride decent continuous vision?

A
  • image quality and unwanted phenomenon like glare, halos, etc
  • minimal success, surgeons hate it
30
Q

Claim is to provide continuous vision and at the same time minimize unwanted phenomena

A

Extended range of vision IOL (extended depth of focus IOL)

31
Q

What is the holy grail of IOLs?

A

Accommodative IOLs

32
Q

Mimics the natural behavior of the lens

A

Accommodative IOL

33
Q

Accommodative IOLs proved additional ______ of vision compared to monofocal lenses

A

1D

34
Q

What is the additional 1D of power in IOLs from

A

Not due to accommodation but because of the optical effects of DoF and lens design

35
Q

Is the accommodative IOL actually accommodative?

A

No, even though FDA certified it as so, it is actually a monofocal with good image quality that adds 1D of DoF

36
Q

Does the accommodative IOL change shape?

A

No, it changes postion, not shape, and that does not contribute to accommodation

37
Q

Current changes in IOL industry

A
  • smaller incision-under 2mm, lens needs to be able to fold to fit in there
  • PCO-posterior capsule opacification
38
Q

PCO-posterior capsule opacification

A

Lens epithelial cell (LEC) growth

  • lens materials (biocompatibility
  • lens edge (square/smooth)
39
Q

What do patients with PCO suffer with

A

Decreases VA, impaired contrast sensitivity, and glare disability

40
Q

How is PCO treated

A

Easily by No:YAG laser capsulotomy

Optics II block 5 (11 decks)

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