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Nilsu Atilgan, YINGZI XIONG, Gordon E Legge; Print Size and Display Size Constraints on Reading with Reduced Acuity. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5941. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
A Critical Print Size (CPS) is required to attain maximum reading speed. When the CPS is large, as in low vision, fewer characters can fit on a display. For small displays and large print, the number of displayable characters diminishes. We sought to discover the minimum number of displayable characters that can support maximum reading speed, and how this Critical Character Count (CCC) interacts with CPS in determining reading performance.
Normally sighted subjects read short stories from Grimm’s Fairy Tales in one-minute trials from which reading speed (words per minute) was determined. The stories were presented on a monitor in three different display configurations corresponding to actual laptop, tablet and phone display sizes. Fourteen subjects read with Times New Roman, and sixteen subjects read with Courier. All subjects read in a normal-acuity condition and a low-acuity condition with blur goggles (effective acuity of 20/135). For each condition (font x acuity x display size), stories were presented with 8 different print sizes and their corresponding 8 different character counts. The character counts were matched across the three display sizes and ranged from approximately 5 to 3000 characters.Analysis: The reading speed data were modeled as the joint effect of two exponential functions—one representing the effect of print size on reading speed, characterized by the Maximum Reading Speed (MRS) and a Critical Print Size (CPS); and the other representing the effect of the number of characters on reading speed, characterized by a Critical Character Count (CCC). CPS and CCC were estimated as the values yielding 90% of the MRS.
The average CPS in normal and simulated low-vision conditions were 0.38 and 1.35 logMAR for Times, and 0.32 and 1.22 logMAR for Courier. The CCC was invariant across conditions with no significant main effects of font, acuity, or display. The average CCC across all conditions was 62 characters per display.
A subject’s reading speed is lower than their Maximum Reading Speed when print size is below the CPS or the number of displayable characters is below CCC. For low acuity and small displays, the joint effect of these two factors restricts the range of print size for achieving Maximum Reading Speed and can sometimes prevent subjects from ever achieving their Maximum Reading Speed.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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