Magnification for students with low vision can be simply provided by reducing the viewing distance of the material being read. Young children, except those who are aphakic (without a lens), are able to focus at a working distance of 10cm for a short time. Viewing an object close to their eyes may offer sufficient magnification for some tasks. A short working distance, with or without reading glasses, provides the greatest field of view.
Magnifiers, also known as “low vision devices” or “optical aids”, can be used to augment residual vision. They vary considerably in type, cost, portability and function and include simple hand-held or stand magnifiers, and hand-held or spectacle mounted telescopes. Up to 20x magnification is common in optical aids. Higher magnification can be achieved with electronic magnification units.
The choice of a suitable magnifier should be made in conjunction with the student's optometrist or staff of the Low Vision Clinic to ensure optimum optical conditions for the student. It is also possible to purchase magnifiers “off the shelf” (see below). The choice is always a compromise between the following characteristics:
In an article printed in the Spring 2000 edition of Lighthouse International's EnVision Newsletter Anne Corn (Professor of Special Education, Peabody College, Vanderbilt University, Nashville, Tennesee) identifies four factors in addition to the right prescription which need to be considered when determining suitable magnification devices for children:
Motivation: Optical devices can allow children who are visually impaired to participate in activities requiring detail vision. With a monocular, for example, a child can sit with her classmates while her teacher reads a picture story. Older students can read bulletin board postings that are not available in large print.
Appearance Makes a Difference: Children want to fit in their peer group and may feel self-conscious using “obvious” devices. Hand-held magnifiers and monoculars should be chosen with appearance in mind. Young children may like to decorate their devices and carrying cases.
Duration of Activity Affects Skills: Begin with activities of short duration, such as reading a wristwatch or an item on a menu, to help children get started using near vision devices. Learning to use a device well before it's needed in the classroom is advantageous.
Quick Retrieval of Devices and Coordination Are Important: Children should be taught good mechanical skills, including one-hand focusing of monoculars, as well as how to change the angle of a hand-held magnifier to accommodate light and comfort.
Distance vision devices are useful for viewing the blackboard, watching sporting events, checking bus destinations etc. Distance viewing can be provided with either a monocular or binoculars, however both reduce the visual field to around 10 degrees. Typically 4x, 6x, or 8x magnification is available - generally the larger the magnification, the smaller the field of view.
A shorter working distance may have the same effect as using a distance magnifier. For example, watching the television with a 2x distance magnifier will be the same as halving the viewing distance.
Distance electronic magnification units may offer additional features, for example:
See electronic magnification units for further information.
Near Vision Devices - Magnifiers
View examples of near vision aids:
Simple hand-held, bar or stand magnifiers can provide enlargement for near vision tasks such as reading a novel, studying a map, or viewing a price in a shop etc. Hand-held magnifiers are often smaller and more portable. Stand magnifiers may be a better option for prolonged tasks, as a suitable working distance is maintained. They can also be useful as a means of keeping the place when working from a textbook to a workbook.
Electronic magnification unit such as the relatively portable Pocket Viewer or QuickLook consist of a television camera, light source and small screen. Near electronic magnification units may offer additional features, for example:
See electronic magnification units for further information.
Successful use of a magnifier is a sophisticated skill, particularly for children, and generally requires considerable training and practise.
See also Large Print or Low Vision Aids - Advantages and Disadvantages, Teaching the Use of Magnifiers for Reading, Reading Exercise Charts, Ideas for Encouraging Reading with a Magnifier