Methods of maximising visual performance

Question 1

What is magnification?

Answer 1

Increasing the size of an image, making it easier to see. Can be done via optical or non-optical devices.

Question 2

How can you predict near VA using distance VA?

Answer 2

Divide distance VA by 3
e.g. 6/24 = N8

Question 3

Why is it better not to predict near VA?

Answer 3

Other factors can affect near VA positively or negatively.
e.g. sentences increase VA because of meaningful context but crowding can reduce VA

Question 4

What optical LVAs can be given for distance tasks?

Answer 4

Telescopes

Question 5

What optical LVAs can be given for near tasks?

Answer 5

Stand Mag
Hand Mag
Spec Mag
Near telescope

Question 6

What should you do once a magnifier has been chosen?

Answer 6

Assess VA with the aid and adjust mag if needed
Advise which rx needs to be used with it
Explain how to use, how to clean and change batteries if relevant
Provide training if available

Question 7

Which rx is usually used with distance telescopes?

Answer 7

Distance

Question 8

Which rx is usually used with hand mags?

Answer 8

Distance if pre-presbyopic
Near if presbyopic

Question 9

Which rx is usually used with stand mags?

Answer 9

Near

Question 10

How often should follow ups be?

Answer 10

3 weeks (phone call)
Yearly or when difficulties experienced

Question 11

What are the likely causes of an LVA not being successful?

Answer 11

VA reduction
Aids used incorrectly or for the wrong task

Question 12

What is the acuity reserve?

Answer 12

2:1

Question 13

What is the contrast sensitivity reserve?

Answer 13

10:1

Question 14

What is the magnification formula?

Answer 14

M=F/4

Question 15

What are the types of magnification?

Answer 15

Relative distance
Relative size
Angular
Display/projection
Total/combined

Question 16

What can be done on a phone or tablet to make things easier to see (electronic magnification)?

Answer 16

Increased font size
Enhanced or reverse contrast
Increased luminance
Software e.g. text reader

Question 17

What can electronic vision enhancement systems (EVES) provide?

Answer 17

Projected magnification
Relative distance magnification
View printed and handwritten text
Binocular viewing

Question 18

What are some examples of electronic magnification?

Answer 18

Video magnifiers
Classroom
Sharing
Portable
Pocket
Headmounted

Question 19

What is a spectacle magnifier?

Answer 19

Glasses with increased add to provide extra magnification
Can be SV or Bif (franklin split or prism-controlled)

Question 20

What are the advantages of spec mags?

Answer 20

Convenient - hands free
Good FOV
Allows scanning
Solution to reading difficulties
Can make in practice
Corrects RE
Allows normal reading posture
Can combine with other mags
Can use NHS vouchers
Cosmetically and psychologically acceptable
Can add coatings/tints

Question 21

What are the disadvantages of spec mags?

Answer 21

Close WD (Convergence harder when WD <25cm, and physically constraining)
Need extra lighting
Period of adaptation
Limited mag and depth of field
Abberations

Question 22

What are the types of spectacle magnifiers you can get?

Answer 22

High add buttons
Binocular readymade 4-14D with BI prism (aids with convergence)
Monocular readymade 12-48D
Bifocals
Glazed units with built in illumination
Clip ons
Headbands
Monocles

Question 23

What size print is acceptable for spot reading?

Answer 23

N8

Question 24

How much magnification does a +4.00 add at 25cm provide?

Answer 24

1x

Question 25

What size print is acceptable for fluent reading?

Answer 25

N4

Question 26

How much mag does a +12.00 add at 8cm add provide?

Answer 26

3x

Question 27

What is the relationship between WD and add power?

Answer 27

Higher add = shorter WD

Question 28

How much prism do you need to add to binocular spectacle magnifiers to aid convergence?

Answer 28

1^ BI for every dioptre above 4D

Question 29

What should you consider when giving a binocular aid?

Answer 29

Binocularity is difficult to maintain above +10D If VA unequal (likely), poorer eye may reduce acuity If nystagmus present

Question 30

What are the advantages of hand mags?

Answer 30

Cheap relative to other aids Acceptable WD and cosmesis Can be illuminated Easy to transport Ok for uneven surfaces Most are battery operated

Question 31

What are the disadvantages of hand mags?

Answer 31

Not good for those with poor grip or shaky hands Uses one hand Limited mag (up to 12.5x) Poor image if not aspheric Must be used at focal point (from page)

Question 32

What are the advantages of stand mags?

Answer 32

Available in higher mag than hand mags Steady Easy to use - at correct WD Some tilt towards px Even illumination Almost hands free Reasonable price

Question 33

What are the disadvantages of stand mags?

Answer 33

Poor FOV if high mag Bulky and heavy Needs a flat, stable surface Small working space underneath (esp if high power) WD from eye to mag depends on reading add Need to know the vergence from the system to determine what specs need to be worn

Question 34

Why do you need to know the image position?

Answer 34

To be able to calculate accommodation or readers needed (most have shorter WD than needed) Image is what the user views, not the object

Question 35

What are the advantages of neck/chest mags?

Answer 35

Hands free Can adjust distance Useful for hobbies

Question 36

What are the disadvantages of hand mags?

Answer 36

Limited mag due to large size

Question 37

What is the maximum mag of a dome or bar mag?

Answer 37

2x

Question 38

What is the definition of a telescope?

Answer 38

Two or more lenses separated by a gap causing an increase in the incident angle of incoming light

Question 39

What are some advantages of telescopes?

Answer 39

Only non-electronic form of distance mag Longer WD Can be binocular

Question 40

What are some disadvantages of telescopes?

Answer 40

Max 3x for distance spec form Expensive Poor cosmesis Heavy Restricted FOV Training needed Exacerbates hand or head tremor

Question 41

What do the markings on a telescope represent? e.g. 8x 20 7.5

Answer 41

Magnification (8x) Objective lens diameter (20mm) FOV (7.5 degrees)

Question 42

What are the characteristics of a Galilean telescope?

Answer 42

Negative eyepiece Positive objective lens Erect image Eyepiece numerically stronger than objective

Question 43

What is the calculation for the length of a Galilean telescope?

Answer 43

Length = Objective focal length - eyepiece focal length

Question 44

What is the calculation for the magnification of a Galilean telescope?

Answer 44

Eyepiece power : Objective power

Question 45

What are the characteristics of an Astronomical telescope?

Answer 45

Both lenses positive Eyepiece stronger power Inverted image (prism corrects) Better image quality than Galilean

Question 46

What is the calculation for the length of an Astronomical telescope?

Answer 46

Length = eyepiece focal length + objective focal length

Question 47

Why does an astronomical telescope give better image quality than a Galilean telescope?

Answer 47

Exit pupil of telescope is coincident with px's pupil so more light enters px's eye

Question 48

How can you differentiate between the two types of telescope?

Answer 48

Galilean: with movement of exit pupil Astronomical: against movement of exit pupil

Question 49

What is the max mag for a Galilean telescope?

Answer 49

2-3x

Question 50

What is the max mag for a Astronomical telescope?

Answer 50

10-12x

Question 51

What order should you train someone to use a distance telescope?

Answer 51

Spotting Focussing Scanning Tracking

Question 52

What are the advantages of near telescopes?

Answer 52

Longer WD More hands free space

Question 53

What are the disadvantages of near telescopes?

Answer 53

Poor cosmesis Increased weight Reduced FOV Limited depth of focus

Question 54

What are some non-optical devices which may help a low vision px?

Answer 54

Talking books Talking clock/watch Liquid level indicator Bump ons High-vis tape Typoscopes Writing frame Large button phone Audio description High contrast utensils Bookstand Clipboard

Question 55

What type of bulb is better for task lighting and why?

Answer 55

Low energy compact fluorescent (cool, low running cost, uniform white light)

Question 56

What are the types of glare?

Answer 56

Disability Discomfort Reflection

Question 57

How can glare be minimised?

Answer 57

Pinholes/typoscopes Change or adapt lighting Reverse contrast Filters/tints/reactions Hat wearing