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Ophthalmic Optics > 10 - Spectacle Magnification (Exam 3) > Flashcards

10 - Spectacle Magnification (Exam 3) Flashcards

(51 cards)

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1
Q

How are anisometropia and antimetropia different?

A

Anisometropia is a difference in lens power between the two lenses
Antimetropia is a difference in sign of lens power between two lenses

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2
Q

What challenge does a large difference in lens power between eyes bring?

A

Difference in spectacle magnification

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3
Q

What is the formula for spectacle magnification?

A

Retinal image size (corrected) divided by Retinal image size (uncorrected) for the same eye

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4
Q

How is spectacle magnification expressed?

A

As a ratio (1.05 is equal to 5% magnification)

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5
Q

How is the normal image size taken?

A

The image size for an emmetropic eye with +60D refractive power

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6
Q

What 2 factors contribute to magnification (or minification) of an image?

A
  1. Power of the lens

2. Shape of the lens

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7
Q

What 2 parameters are included in the power factor of a lens?

A
  1. Vertex distance

2. Back vertex power

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8
Q

What 3 parameters are included in the shape factor of a lens?

A
  1. Lens thickness
  2. Index of refraction
  3. Front base curve
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9
Q

What is the formula for shape factor?

A

1 divided by 1-((t/n)f)

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10
Q

What is the formula for power factor?

A

1 divided by 1-dP

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11
Q

What are the units for lens thickness in the shape factor equation?

A

Meters

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12
Q

What are the units for vertex distance in the power factor equation?

A

Meters

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13
Q

What is spectacle magnification equal to?

A

Product of shape factor and power factor

shape factor)(power factor

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14
Q

What is the formula for relative spectacle magnification?

A

Image size for corrected ametropic eye divided by image size for standard emmetropic eye

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15
Q

What does Knapp’s Law state?

A

Refractive error caused by axial ametropia can be corrected by thin lenses positioned 15mm in front of the eyes

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16
Q

Do spectacle lenses follow Knapp’s Law?

A

No

They are not thin, flat lenses

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17
Q

What is the best way to correct patients with refractive ametropia without changing retinal image size?

A

Contact lenses

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18
Q

What is the normal magnification of an uncorrected emmetropic eye?

A

1.00

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19
Q

What do plus lenses give in terms of magnification?

A

Gain in magnification (>1.00)

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20
Q

What do minus lenses give in terms of magnification?

A

Loss in magnification (<1.00)

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21
Q

Where is the entrance pupil for the eye located?

Study These Flashcards
A

3 mm behind the cornea

22
Q

How is the ‘d’ value found for the power factor of a lens?

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A

vertex distance plus 3 mm

23
Q

For a myope, will CLs or spectacles result in a smaller loss of magnification?

Study These Flashcards
A

Contact lenses

24
Q

For a hyperope, will CLs or spectacles result in a smaller gain of magnification?

Study These Flashcards
A

Contact lenses

25
What other problems result in symptoms similar to aneiseikonia?
Refractive error and oculomotor imbalance
26
What are 4 indications of clinically significant aneiseikonia?
1. High anisometropia/ high astigmatism 2. Physical alterations to the eye (IOL, LASIK, etc.) 3. Complaints of spatial distortion 4. Monocular vision is more comfortable
27
What is aneiseikonia?
Dissimilar retinal image size
28
What are the 4 types of aneseikonia?
1. Physiological aniseikonia 2. Symmetrical aniseikonia 3. Meridional aniseikonia 4. Asymmetrical aniseikonia
29
What is significant about physiological aniseikonia?
Allows for the perception of depth
30
What is symmetrical aniseikonia?
Images equally larger or smaller in every meridian
31
What is meridional aniseikonia?
Symmetrical, but meridional size difference in the eyes | Can be along any meridian
32
What is noticed with asymmetrical aniseikonia?
Progressive increase or decrease across the visual field
33
What are the 2 types of ametropia?
1. Axial ametropia | 2. Refractive ametropia
34
What is the best way to correct ametropes with refractive ametropia to prevent aniseikonia?
Contact lenses
35
How can you tell clinically whether a patient's ametropia is axial or refractive?
Keratometry findings | Significant differences signal refractive ametropia
36
What is the best way to correct anisometropes with high astigmatism?
Contact lenses
37
What are 4 methods of reducing aniseikonia with spectacles?
1. Short vertex distance 2. Small eyesize frame 3. Aspheric lenses 4. High index lenses
38
What may be necessary to correct with presbyopes that have aniseikonia?
Vertical imbalance | via Slab off
39
What is another term for iseikonic lens?
Size lens
40
When correcting aniseikonia, should aspheric lenses be used in just the right or left lens?
No | Aspheric lenses should be used OU
41
What is the minimum center thickness for finished poly/trivex lenses?
1.0 mm thick
42
What is the minimum center thickness for semi-finished poly/trivex lenses?
1.5 mm thick
43
What is the expected base curve for a minus lens?
Flatter than +6.00D
44
What is the expected base curve for a plus lens?
Steeper than +6.00D
45
What is the minimum vertex distance for spectacles, and what does a smaller distance result in?
11 mm | Lash crash
46
What is the industry standard for minimum center thickness of a lens?
2.0 mm
47
At what percent of retinal image size difference can patients reliably fuse 95% of the time?
3.90 to 3.99%
48
If you can't get retinal image size difference to just below 4%, should you force it and risk poor cosmetics?
No | Patients are likely already monocular at this point
49
What 4 components of a lens can be altered in iseikonic lens design?
1. Front base curve 2. Index of refraction 3. Vertex distance 4. Center thickness
50
When dealing with aniseikonia, should you add magnification or minification?
Always add magnification to the eye that has less
51
What are 3 ways to increase magnification in any lens?
1. Steepen the front base curve 2. Increase center thickness 3. Increase vertex distance

Ophthalmic Optics (10 decks)

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