Issues and Strategies for Visually Impaired Learners
Tuesday 7 March 2006
Low Vision Aid (LVA) Training
Low Vision Aids
- Common visual problems discussed.
- Visual abilities (Near, Distance and Field of Vision).
- Objective Assessment of the eyes.
Note: In the first video we saw simulations of common visual impairments. It was shown that by using distance and near acuity, an approximate magnification for a particular child could be predicated, assuming a correct and reliable spectacle prescription.
Presumption of mainstreaming
- Current educational policy to educate ALL children within a mainstream provision – with few exceptions.
- It is of the utmost importance that any potential barriers are removed.
- VI pupils must be encouraged to use low vision aids correctly.
Low Vision Aids
The aids can be divided into three basic categories:
- Basic or low technology magnifiers.
- Mid-range technology magnifiers.
- High technology magnifiers.
Note: Basic: hand held magnifiers stand magnifiers both illuminated and
non-illuminated flat bed magnifiers and line magnifiers.
Mid range spectacle mounted LVAs and telescopes both spectacle and non-spectacle mounted.
High technology magnifiers such as video magnifiers.
- Low tech magnifiers generally assist a child's near visual acuity and are used for reading or close up work.
- Usually a simple lens surrounded by a ring of plastic and supported by a plastic handle.
- Loupes folding device where lens doubles up on itself into a metal or leather housing.
Note: Simplest and most widely used form of LVA. –Powers range from +4 to +20 dioptres. ( From the first video the relationship between dioptres and magnification should be remembered as 4 dioptres equals 1 times magnification. Above +20 referred to as loupes range extends to approx. +64 dioptres or 16 times magnification.
- Hand held magnifiers can be used in conjunction with normal distance or reading spectacles.
They MUST be used at a distance from the eye, close to the magnifier focal length.
Note: If reading spectacles are used then teach the child to set a constant distance from the eye to the magnifier and to bring the print in from behind.
- Available in illuminated and non-illuminated forms with magnification of up to times 20. (Can be used with spectacles.)
- Need to be held at a relatively close working distance to the eye.
Low tech: Flatbed magnifiers.
Designed to be used in contact with the working plane or reading material.
Main advantages: Light gathering properties (make them highly efficient under diffuse lighting conditions such as daylight) and lack of optical distortion.
Disadvantages: weight small size and need for flat surface.
Note: If the child holds the magnifier 4 to 5 mm from the page they are increasing the magnification which may be an indication that more magnification is required.
Low Tech: Line or bar magnifiers
Same principle as flatbed magnifier.
Same advantages and disadvantages
BUT shape makes them better for reading lines of text: some have a an in-built line and finger grip for easy manouvrability.
Mid Tech : Spectacle Mounted Magnifiers.
- In its simplest form a spectacle mounted magnifier is a pair of convex or positive lenses, mounted in a spectacle frame.
- These will give the user the maximum field of vision combined with the minimum weight and acceptable thickness.
Note: All lenses are manufactured from plastic and are thus light and comfortable to wear.
Mid Tech: 'Clip over' type aid.
- These are positive lenses mounted in front of spectacles and can be monocular or binocular form.
- Attached to spectacles by a bulldog or spring clip arrangements.
- Often lenses flip up allowing the wearer to use the distance portion of the spectacles.
Mid Tech; Telescopic Aids
Considerate positioning of a child in the classroom can go a long way in assisting their distance acuity.
- Two basic types; the Galilean and Keplerian.
- Variable focus
- Fixed focus.
Note: Simplest and most practical way to improve distance acuity is to reduce the distance between the eye and the object. By halving the working distance, the retinal image size is automatically doubled and the image quality is unimpaired.
Variable focus telescopes able to focus on distant objects and by rotating the metal housing on near objects too. Magnificatin range 2.75 to 10 times.
Fixed Focus lack variable focus element but can be used inconspicuously at the theatre etc.
High Tech; Video Magnifiers(CCTVs)
Tend to be used by more severely visually impaired who require a higher magnification than can be obtained using an optical type aid.
- More modern systems are more portable and have more facilities.
- Major uses for reading although can be used for distance.
- Magnification levels can be set by the user.
- Greater freedom of working distance reduction in user fatigue.
LVAs Common complaints
Stand magnifiers : impeded speed of reading due to small field. Head and neck pain. Cannot read and write at the same time.
Need to use sloping board, further assessment.
Distance telescopes; Loss of orientation, difficulty in locating objects, field of view is too small for television viewing.
1. An LVA can be an invaluable assistance to a child with impaired visual acuity.
2. The prescribed LVA must be concurrent with the child's visual ability and the tasks the child has to do.
3. Children should be assessed for LVAs regularly (at least yearly, during transitions).
4. Training in the use of LVAs is essential.
Low Vision Aids: Main Points.
- Vision assessed by an optometrist
- Planned introduction and regular assessment of the child using low vision aids.
- A structured training programme.
Presentation prepared using training notes from Video entitled 'Effective Management of children with a Visual Impairment' which was produced by The University of Birmingham Dr H Mason.