One of the first tools that many people with visual difficulties reach for is a low vision magnifier. A magnifier makes an image look larger so it seems intuitive that people will grab a magnifier with the highest power. After all, making print look larger will make things easier to read right?
While a magnifier does increase the size of an image, it comes at the cost of decreasing a field of view. This can have a negative impact in the following ways:
For example, you are looking at a word through a finite sized screen. Using the highest magnification possible, the image of the word becomes so big that it fills up the entire screen and you can now only see a single letter. While you can clearly see the ink of the letter, you now have another problem. You are so zoomed in that you cannot tell what the word is. This leads to an important point – increasing magnification in turn decreases field of view and when the field of view becomes excessively small, you may lose context of the object you are looking at.
Now imagine that you have a smudge on a window. Look at the picture above. With greater magnification, the small smudge appears larger in size and more difficult to ignore. Similarly, high magnification may not be appropriate for patients with localized spots of distortion or missing field as the result of certain eye diseases, such as macular degeneration. Making these distorted spots larger in a smaller field of view in actuality decreases the proportion of useful or useable visual field.
The last consideration is the effect of movement on a small field of view. Unlike a stationary picture, the image through a handheld magnifier is often subjected to hand tremors. Both photographers and shooters, that use similar magnification devices in their respective fields, are aware that a smaller field of field exaggerates movement more than a larger field of field. A few degrees of movement within a small field of view can change the image entirely while only a mild shift may be noticed viewing in a larger field of view.
Above are a few examples of why bigger is not always better when it comes to magnification. There is always trade-off between increasing image size and decreasing field of view. Using a particular sized field of view may be task-dependent i.e. looking at the tree or looking at the forest. There are also many magnifiers out in the market each with its different features. The best approach is to come up with a specific list of activities that you would like help achieving and let a low vision specialist show you the available options.
To learn more about our Low Vision Services, please take a look at our Adult Services.