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My Own Deck > Visual Impairment 2- Magnification > Flashcards

Visual Impairment 2- Magnification Flashcards

1
Q

What are the 4 ways to enlarge retinal image size?

A

Relative Size magnifiction
Relative Distance Magnification
Angular Magnification
Real image/ Transverse Magnification

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2
Q

What are the advantages to making objects bigger? (RSM)

A

No training required
Less conspicuous
No change in habitual posture
Patient can plan themselves

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3
Q

What are the downsides to enlarging objects?

A

More cumbersome
Limited mag
Loose contrast i.e. enlarging by photocopying

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4
Q

How do we work out magnification when changing the relative distance?

A

M= OLD obj dist/ NEW obj dist

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5
Q

What does angular magnification refer to?

A

Telescopes

Mag= instrument image/obj (s telescopes)

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6
Q

What are some examples of real/transverse imaging?

A

CCTV

TV screens

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7
Q

What formula would be used if different magnification were used with one another?

A

Total mag= relative SIZE mag X relative DIST mag

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8
Q

What are the 2 different types of telescopes?

A

Keplerian/ astronomical

Galilean

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9
Q

Which telescope uses prism to create correct inverted image?

A

Keplerian

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10
Q

Which telescope uses 1 convex and 1 concave lens?

A

Galilean

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11
Q

How high can the magnification go on a keplerian compared to a galilean?

A

Keplerian upto 10x

Galilean up to 4x

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12
Q

Where is the exit pupil located in a keplerian compared to a galilean?

A

Keplerian external

Galilean internal

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13
Q

What is the field size on keplerian compared to a galilean?

A

Keplerian larger

Galilean smaller

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14
Q

Between an eye piece and objective lens which is stronger powered in astronomical?

A

Eye piece

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15
Q

How would you work out the magnification in a telescope

A

M= diam of OBJ LENS/ diam of EXIT PUPIL

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16
Q

Which telescopes would you find markings?

A

Kelperian

17
Q

What would you do to get the maximum field of view in a telescope?

A

Objective lens would need to as large as possible

18
Q

What formula is used to predict the DIST mag?

A

Required/Actual— snellen as decimal

Actual/Required— looking for a denominator

19
Q

What is the formula to predict near mag?

A

Mag required= actual VA/required VA

20
Q

Whats another way to find what VA is required for a specific task?

A

Nomogram

21
Q

What is the typical routine to determine how much mag is needed?

A
  1. ID specific and amoun
  2. Bino or Mono
  3. Select appropriate LVA
  4. Perform trial of suitability
  5. Determine specific correction necessary
  6. Loan device after training
  7. Follow up visits
22
Q

Which is the only useful LVA to use for distance?

A

Telescopes

23
Q

What would a telescope commonly be used for?

A

Outdoor use

24
Q

Whats the main problem with telescopes?

A

FOV!!
Increased mag= SMALLER FOV
Decreased mag= LARGER FOV

25
Q

What is the best LVA to use for manipulative task?

A

Telemicroscopes

26
Q

What rx is used with a telescope used for dist?

A

Dist rx

27
Q

When is a distance rx is used for near?

A

When using a hand held magnifier

28
Q

What are the advantages of telescopes

A

Alter size with altering working dist
Px refractive error incorporated
Focused D+N

29
Q

What are the disadvantages of telescopes?

A 
Restricted FOV 
Not suitable while moving 
EXPENSIVE 
Speed also magnified 
Often requires training
30
Q

What formula is used to find out the accommodation that is required for near vision telescopes?

A

Accom(n) = WD (diopter) x mag(2)

31
Q

Why use telescopes for near?

A

Increase WD compared to spectacle magnifier

32
Q

What is the formula used to workout telemicroscope mag?

A

Mag total= mag telescope x F(power of reading cap) /4

33
Q

What are the disadvantage of telemicroscopes?

A

Heavier if spec mounted
Worse FOV
Cosmetically poor
Costly

34
Q

What 2 types of task could telescopes be used for?

A

Sedentary tasks

Spotting tasks

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