Optical Devices
Stand Magnifier
A fixed focus stand is a convex lens in a rigid mount that has been set by the manufacturer to focus closer to the page than its focal distance, to reduce peripheral aberration. Most stand magnifiers are designed for use with a standard bifocal add or reading glasses.
Powers available: 24 diopters.
Advantages
- They can be handy optical devices because the focal distance is stable.
- They are particularly suitable for patients with hand tremors.
- They are especially useful for patients who have difficulty in finding or maintaining the correct distance when using spectacles or hand magnifiers.
- They are useful for patients with a constricted visual field, when held at arm's length.
- They are also available with a built-in light source, which can be highly effective in enhancing contrast.
Disadvantages
- They have limited mobility, being inconvenient to carry around.
- They are awkward to use on non-flat surfaces; they require the use of a reading stand.
- They have a limited field of view.
- They can cause excess shading and reduce the amount of light on the viewing surface, unless self-illuminated.
- Most available designs make writing difficult, if not impossible.
- Prolonged use of these devices may result in poor posture, unless a reading stand is used.
Glare Control Devices
Glare is distracting scattered light, which is a major problem for patients with low vision. Glare can be controlled with devices such as sun-wear or absorptive lenses, tints and ultraviolet coatings, and anti-reflective coatings.
Absorptive Lenses: (for glare control)
- Tinted sun glasses with side shields: grey, brown and yellow
- Tinted clip-on sun glasses: grey, green and yellow
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