4.2.2 Low Vision Aids

Px eligible for Low vision Aids

• Reduced VA

• Reduced field

• Don’t need to be registered as SI or SSI

• Likely from progressive conditions such as AMD, Glaucoma, DR, Retinitis Pigmentosa - peripheral field loss

Group 1 - SSI

• Worse VA than 6/120 (3/60)

Group 2 - SSI

• VA 6/120 or better, but worse than 6/60

• & contraction of their VF

Group 3 - SSI

• VA 6/60 or better

• With clinically significant contracted VF which is functionally impairing Px

  • E.g bitemporal hemianopia

Group 1 - SI

• VA of 6/120 to 6/60 with Full Field

Group 2 - SI

• VA between 6/60 and 6/24

• & moderate contraction of VF

Group 3 - SI

• 6/18 or better, with marked field defect

  • e.g homonymous hemianopia

Certificate of Vision Impairment (CVI) - completed by Ophthalmologists

• Info regarding details of disorder, VA, fields and difficulties the px is having

• Name, address, DOB

• Establishes the Ophthalmologist believes the requirements are met - formally classifies Px as SSI/SI

• Starts the process of registration

• 5 copies - Px, Local Authority, Px’s GP, Hospital notes, Epidemiological analysis e.g Moorfields 

• Home visit to see the environment/look at modifications

Referral of Visually Impaired Patient (RVI) - completed by non-ophthalmologist clinic staff to refer

• Info about px condition, problems with daily life

• Only Hospital staff can complete this

• Must have consent of px to refer

• For Px where registration is not appropriate

• Referred to social services due to struggling with eyesight

• Simply flags the px to local authority to see if the px can be assessed for any help

• 4 copies - Social S, Px, Px GP. Hospital file

Low Vision Leaflet (LVL)

• Self-referral leaflet to the Social Services

• Local opticians who can give to px who are struggling

Where can Low vision services provided?

• Hospital eye departments - recommend low vision aids - advice on contrast, lighting and daily tasks

• Community Optometry Low vision Services

• Charities - RNIB - counselling - training in the use of aids

• Rehabilitation services - Local authority - rehab training for daily tasks, mobility and orientation support, home assessments and adaptations

• Guide Dogs for Blind association - apply for a guide dog

• Uni Eye Clinics

Assistive Technology

• BlindSquare – App describes environment and announces points of interests/streets/specified points as you travel

• iDentifi – Voiceovers objects in the camera screen - recognises objects and brands so helps with grocery shopping

• Be My Eyes – App matches visually impaired user with sighted volunteer for help - free unlimited calls - real time assistance

• SeeingAI - narrates the world around the px - helps with reading, describing photos and identifying products

• VoiceVista - helps VI Px with their surroundings - audio navigation app - gives directions and helps find places - has a sound beacon which helps stay on route

• Reverse contrast

• Increasing size on the screen

• Kindle - contrast and size of print

Large Print Books

• No change in posture/distance

• Simple, no training req.

• Less conspicuous

Disadvantages

• Limited in size

• Reduces contrast

Deciding between monocular or binocular MAG

• If VAs are similar then Bino. is preferred

• VA’s are not similar use Monocular - use the best VA eye

• Design of Magnifiers may force it the be used monocularly

What option do we have to hence distance mag

• Telescope is the only useful aid

• In some cases you can move closer e.g TV

When using a distance telescope does the Px need to wear specs?

• Can be used with or without specs

• Largest FOV is obtained when exit pupil is closest to the eye

What Rx does the Px wear for Hand MAG?

• Distance RX

Spectacle Microscope

e.g px is -4.00 and needs 3x mag

• MAG = F/4

• F = +12.00DS

• Take into account Rx

• Final Lens = +8.00DS

What is the FOV for telescopes?

• Restricted at 7 degrees - 1 degree = 1cm viewed at 57cm

  • Difficult to walk around and view - good for spotting tasks such as Bus numbers and watching TV

Adv of telescopes

Types of telescopes

Keplerian - img is inverted - prism used to rotate the lens - greater mag

Galilean - no prism

Pros of Near Telescopes

• Increased WD compared to Spec Mag

Cons of Near Telescopes

When compared to spec microscope;

• Worse FOV

• Cosmetically poor

• Costly

• Heavier

Hand Magnifiers

• Best Known LVA - easy to use

• Widely available

• Higher power = smallest lens diameter

What happens at the FP of the magnifier?

• MAG is greatest

• FOV is smallest

• Parallel rays of light emerge - no need to accommodate

Summary of Hand Magnifiers

• Plus lenses - increase retinal image size via RDM

• Allows Px to adopt a closer WD

• If object is placed at anterior FP of lens - Distance Rx

• If object is closer than Anterior FP - Reading Rx/ Near ADD

Advantages of Hand MAGs

• Discrete

• Easy to use

• Portable

• Lightweight

• Convenient for brief tasks e.g labels

• Inexpensive

• Can use internal illumination

• Used with distance Rx

Disadvantages of Hand Mags

• Handling - require a hand + needs to be steady

• Restricted FOV

• Can cast shadows over object

In a stand magnifier why is the object to lens distance LESS than the FP of the lens?

• Provides a better quality image c less aberrations

Diverging light leaves the mag - Px must accommodate / Reading ADD

ADV of Stand Magnifiers

• Accurate WD

• Hands free

• Contains internal illumination

DisAdv of Stand Magnifiers

• May require special reading specs

• Stand can prevent assess to object

• Flat surface required

• Can be more bulky than hand mags

What would be the power for a low powered stand mag?

• around 4x mag

What would be the power for a med/high powered stand mag?

• from 4 to 20x mag

• z closer to 0

Dome Magnifier

Advantages;

• Great for instantly enlarging text on a book

• Rests on the page – does not have to be held up by the patient.

Disadvantages;

• Can be somewhat heavy & fiddly – not ideal for patients with arthritis etc.

Spectacle Rx

Advantages;

• High Plus Rx may replace a magnifier

• Hands free

Disadvantages;

• Lenses are heavy

Galilean over Keplerian?

• Lighter, shorter and cheaper

Keplerian over Galilean

• Widens FOV, better quality img than Galilean

Non-Optical LVA

Tints - Dark for albinism or RP, yellow for CS in AMD

Caps/Visors to reduce glare

Typoscopes - flat sheet of card or plastic that helps isolate a line - improves contrast and helps maintain place when reading text

Extra illumination for AMD, Glaucoma, DR, RP

CCTV

• Variable high levels of magnification

• Reverse contrast

• Reduced visual crowding

• Improved illumination

• Up right view posture - reduces neck and back strain compared to other LVAs

• Desktop systems/hand held units

COST

Learning curve

Portability