Visual Impairment 2- Magnification

Question 1

What are the 4 ways to enlarge retinal image size?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

What are the downsides to enlarging objects?

Answer 3

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

Question 4

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

Answer 4

M= OLD obj dist/ NEW obj dist

Question 5

What does angular magnification refer to?

Answer 5

Telescopes

Mag= instrument image/obj (s telescopes)

Question 6

What are some examples of real/transverse imaging?

Answer 6

CCTV

TV screens

Question 7

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

Answer 7

Total mag= relative SIZE mag X relative DIST mag

Question 8

What are the 2 different types of telescopes?

Answer 8

Keplerian/ astronomical

Galilean

Question 9

Which telescope uses prism to create correct inverted image?

Answer 9

Keplerian

Question 10

Which telescope uses 1 convex and 1 concave lens?

Answer 10

Galilean

Question 11

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

Answer 11

Keplerian upto 10x

Galilean up to 4x

Question 12

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

Answer 12

Keplerian external

Galilean internal

Question 13

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

Answer 13

Keplerian larger

Galilean smaller

Question 14

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

Answer 14

Eye piece

Question 15

How would you work out the magnification in a telescope

Answer 15

M= diam of OBJ LENS/ diam of EXIT PUPIL

Question 16

Which telescopes would you find markings?

Answer 16

Kelperian

Question 17

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

Answer 17

Objective lens would need to as large as possible

Question 18

What formula is used to predict the DIST mag?

Answer 18

Required/Actual— snellen as decimal

Actual/Required— looking for a denominator

Question 19

What is the formula to predict near mag?

Answer 19

Mag required= actual VA/required VA

Question 20

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

Answer 20

Nomogram

Question 21

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

Answer 21

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

Question 22

Which is the only useful LVA to use for distance?

Answer 22

Telescopes

Question 23

What would a telescope commonly be used for?

Answer 23

Outdoor use

Question 24

Whats the main problem with telescopes?

Answer 24

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

Question 25

What is the best LVA to use for manipulative task?

Answer 25

Telemicroscopes

Question 26

What rx is used with a telescope used for dist?

Answer 26

Dist rx

Question 27

When is a distance rx is used for near?

Answer 27

When using a hand held magnifier

Question 28

What are the advantages of telescopes

Answer 28

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

Question 29

What are the disadvantages of telescopes?

Answer 29

``` Restricted FOV Not suitable while moving EXPENSIVE Speed also magnified Often requires training ```

Question 30

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

Answer 30

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

Question 31

Why use telescopes for near?

Answer 31

Increase WD compared to spectacle magnifier

Question 32

What is the formula used to workout telemicroscope mag?

Answer 32

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

Question 33

What are the disadvantage of telemicroscopes?

Answer 33

Heavier if spec mounted Worse FOV Cosmetically poor Costly

Question 34

What 2 types of task could telescopes be used for?

Answer 34

Sedentary tasks | Spotting tasks