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The necessary field of view to read with an optimal stand magnifier
E M Fine1, M P Kirschen, E Peli
1Wilmer Eye Institute, Johns Hopkins University, Baltimore, MD 21205, USA.
Background:
For most people with low vision, some form of magnification is necessary to read. Using a magnifier reduces the number of letters that can be seen simultaneously (field of view), which has been shown to decrease reading rates. This study sought to determine how many letters are necessary to attain maximal reading rates with a stand magnifier.
Methods:
Younger and older normally-sighted and visually-impaired observers read short passages using a fiber optic stand magnifier (taper). The optical properties of this magnifier allowed the field of view to be precisely varied. Each subject read using at least four field sizes (3, 5, 9 and 13 characters visible) while reading speed was measured.
Results:
Reading rates continued to increase with as many as 13 characters visible, regardless of age or vision status. In addition, reading with the taper was slower for all subject groups than reading without the magnifier.
Conclusions:
This study confirms reports that reading rates increase as the field of view increases when reading from a page of text. The need for this large field of view relative to other low vision reading aids (i.e., computer-generated scroll displays) is likely the result of the readers' need to actively navigate across the page of text.