4.2.2 Understands the application of complex low vision aids.

Question 1

Telescopes

Answer 1

 Required for distance magnification when getting closer to the object is not an option
 Usually required when px is mobile for seeing bus numbers, train boards, street names etc
 Small field of view – approx. 7 degrees
 Some px’s prefer larger Fov & reduced VA – not for everyone
o Field of view is optimised by patching size of exit pupil to px’s pupil (or ensure exit pupil is > px’s pupil)
 Can be hand-held for spotting tasks or spec mounted – rare that they can be worn FT
 2 types: Astronomical/Keplerian & Galilean:

Question 2

Electronic

Answer 2

 Most common of real image magnification is the use of a closed-circuit television (CCTV)
 Mag is calculated as M = size of image/size of original object
 Image quality depends on screen resolution)
 Maximum mag achievable by optical magnifiers is about 20X (80D), this can be up to 70x with electronic aids, but limit of about 30x is common
 Variable magnification may also be useful if the patient’s eye condition changes

 Electronic features (advantages)
o Foreground/background colour options, windowing etc
o Contract, luminance, enhancing
o Contrast reversal (50% of VIP prefer white on black)

Question 3

Advantages of EVEs

Answer 3

• Aberration free
• Max mag up to 70x higher (limit of 30x is common)
• Zoom controls allow variable magnification
• Foreground/background colour options, windowing etc
• Contract, luminance, enhancing
• Contrast reversal (50% of VIP prefer white on black)
• Binocular viewing
• Normal viewing distance/posture
• Variable camera-to-task and eye-to-screen distances
• Reading duration > optics LVA
• May be more psychologically acceptable than optical aids
• May be useful if a physical handicap prevents use of aids

Question 4

Disadvantages of EVEs

Answer 4

• Cost: expensive to buy and service/repair
• Size depending on type/model
• Image quality – depends on screen
• Depth of field is limited by the focal length of the camera and can cause problems with thick books (use glass sheet to flatten out)

Question 5

CCTV

Answer 5

• Stand mounted
• Still one of the most commonly used designs
• Each component fixed and mounted vertically “in-line”
• Working space fixed or limited
• For distance need second camera to be added
• Reading material needs to be flat – depth of focus
• Advantages
  o Good of physical handicap
  o Good for extensive VF defects, SES
• Disadvantages
  o Expensive, bulky, servicing and repair
  o Practice required
  o Control positions
  o Depth of field

Question 6

P-EVES, USB reader, Spec, head mounted…

Answer 6

Hand help/portable (P-EVES)
o Greater versatility than CCTV
o Most common type and held at any desired distance
o Cheap, lightweight and portable
o Convenient to carry for short duration
o Usually used with px with distance rx however near can be worn if use a shorter mag-eye distance
o Field of view is directly proportional to diameter of lens and indirectly prop to lens power and eye-lens distance
o May be helpful for px with reduced peripheral fields
o Further lens held from eye- increased distortions and poorer field of view
o Ineffective if used incorrectly with reading RX and difficult to maintain correct position and steady eye strategy for extended times
Television/USB readers
o Low cost & versatile
Spec
o Hands free and used for prolonged reading
o Widest FOV and cosmesis similar to normal specs
o Incorporate astigmatic correction and may be used in px with hand tremor
o Close working distance so illum difficult and cause fatigue, HA and dizziness
o Binoc limited mag, reduced reading speed
Head-mounted video magnification devices
o Distance and near magnification
o Independent of external illumination/reduced glare
o High cost isn’t justifiable – reading speed similar to that with standard CCTV or large print

Question 7

Who benefits/EVES compared to optical LVAs

Answer 7

• Usually young and highly motivated
  o May be linked to congenital visual impairment – poorer VA
  o Distance VA better than 6/90 may gain little benefit from using EVEs
• More useful than magnifiers for very small print only
• Not yet available on NHS
• Available through local libraries/charities, no special schemes for education/employment

Question 8

Adaptations of phone use:

Answer 8

• Bigger - larger text, zoom in, magnifier setting or app
• Contrast - bold text, invert colours, colour contrast
• Brightness - increase it, increase saturation
• Audio - text to voice or audio description

Question 9

Apps:

Answer 9

• Be My Eyes - an app for identification. This allows volunteers that have sight to let them “be the eyes” of the visually impaired person. The moment the person needs help in a given situation, a random volunteer can have a free call with them and grant them guidance. It shows up as a notification which is then clicked to allow the person to see the task needing help with. For example, a person cannot tell the difference between a red or blue jumper and so the volunteer will tell her which is which through video call and even give a complement or additional advice. This is helpful in eliciting social connection and preventing the person with low vision from feeling alone perhaps
• “Colour identify”, “Camfind” or “Tap tap see” - colour identification. Descriptions of objects are spoken back to the person through the speaker of the phone