Best optical low vision aids are commonly used to treat the low vision aids. It is also called as magnifier.
Best optical low vision aids
There are numbers of magnifiers and low vision aids device available. They all have one property in common they are designed to be held close to the reading material to enlarge the image of the print to make it more readable.
Some have battery operated or plug in lights built in which can be of value. The amount of magnification is dependent upon the amount of remaining vision and the size of the material to be seen.
Low vision aids and Magnifiers for near tasks can be used for:
• reading a book or a newspaper
• reading labels, signs or prices in shops
• using tools, for example measuring
• identifying money
Remember the formula:
Multiply the amount of magnification by 4 to get the “Dioptric Power” of the lens. Divide the Dioptric power into the number 40 to get the number of inches from the eye.
HAND MAGNIFIERS
These are plus lenses that are held in front of the spectacle plane.They can be used with or without glasses.
Uses
• Reading signs, labels, prices, books
• Identifying money
• Viewing near objects.
Hand magnifiers are available from +4.0 to + 68.0 Diopter.The quality of the lens is very poor and degraded after +32.0 Diopters. Also higher the power smaller is the lens size of the magnifier and hence reduced field of vision.
The field of view depends on the distance of lens from the eye and the size of the magnifier.
The practitioner can stock single manufacturers or tend to select a few designs and powers from each manufacturer.
Each has a special feature, the design, some with wider field of view, some are lighter, and some are pocket folding models or may have self contained illumination.
The illuminated ones give an advantage of using them wherever the room or the surrounding light is dim.The hand magnifiers are available in 3 basic designs.
• Aspheric,
• Aplanatic,
• Biaspheric.
The trial set should include following ranges of magnifiers – 2X (8 Diopters) to 10X (40 Diopters). Most patients accept up to 6X magnification depending on task and degree of impairment.
The image is viewed with distance vision glasses or through reading glasses in presbyopes.
The trial procedure includes starting with magnifiers from less magnification to higher gradually. Giving time to patient to read with each, to the one he feels most comfortable to hold and read.
Some may prefer less magnification but larger field of view, some may prefer folding shapes, and some want very strong powers to enable them to read the smallest. The selection depends on the patient’s requirements and the task he wants it for.
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Advantages
• The eye to lens distance can be varied with hand magnifiers
• The patient can maintain normal reading distance unlike spectacles and stand magnifiers which make the patient go close.
• It is most convenient for short term tasks
• Many of our elder patients may have picked them over the counters and will be familiar to them.
• They are easily available
• They work well in patients with eccentric viewing
• Diseases with constricted fields will also benefit with them.
• Some magnifiers have their own light source which itself enhances the vision.
Disadvantages
• The major one being that it occupies both hands hence is fair enough for reading but cannot be utilized for writing, or tasks which need the other hand free.
• Maintaining focus is also a problem in some, especially in elderly with tremors and poor manual dexterity.
• The field of vision is also limited while using this device.
Optical Design of the Magnifiers Used as Low Vision Device
1. They can be spherical, aspheric, biaspheric and doublet.
2. They can also be illuminated or non illuminated form.
3. Higher the power the better is the optical quality required. Spherical magnifiers are cheaper ones. Higher the powers poorer will be the optics of the lens because of all types of
possible aberrations a lens can have.
4. Aspheric lens has advantage or reducing thickness and peripheral distortions.
5. Biaspheric magnifiers have advantage of eliminating aberrations from both the surfaces.
6. Aplanatic or doublet magnifiers give a flat and wide distortion free field and good edge to edge clarity.
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Low vision aids