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Yuliya Bababekova, Jennifer E. Hue, Rae R. Huang, Mark Rosenfield; Font Size and Viewing Distance of Hand-Held Smart Phones. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2840.
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The use of hand-held smart phones for written communication is becoming ubiquitous in modern society. The relatively small screens found in these devices may necessitate close working distances and small text sizes, which can increase the demands placed upon accommodation and vergence. This can result in disabling symptoms either at near or when looking into the distance after prolonged use. The aim of this study was to measure both font size and viewing distance while individuals were using hand-held electronic devices.
Smart phone font size and viewing distance were measured in two separate studies. In the first study (N=129), subjects were asked to show the examiner a typical text message on their own personal phone. The vertical height of a lower case letter without ascenders or descenders was measured to the nearest half millimetre through a +20.00D lens. Additionally, subjects were asked to hold the device "as if they were about to type a text message", and the distance from the smart phone to their spectacle plane was measured using a rigid tape measure. A second trial was conducted in a similar manner except subjects (N=100) were asked to view a specific web page from the internet.
For text messages and internet viewing, the mean font size was 1.12M (SEM=0.02; range 0.7 to 2.1M) and 0.78M (SEM=0.03; range 0.34 to 1.38M), respectively. The mean working distance for text messages and internet viewing was 36.2cm (SEM =0.63; range 17.5 to 58.0cm) and 32.2cm (SEM =0.74; range 19 to 60cm), respectively.
The mean font sizes for both conditions are comparable with newspaper print, which generally ranges between 0.8 and 1.2M. However, the mean working distances were closer than the typical near working distance of 40cm for adults when viewing hardcopy text. These close distances will place increased demands upon both accommodation and vergence, which could exacerbate symptoms. Practitioners need to consider the closer distances adopted while viewing material on smart phones when examining patients and prescribing refractive corrections for use at near, as well as when treating patients presenting with asthenopia associated with nearwork.
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