iPhone 4 311 R.
(photo credit: REUTERS/Truth Leem)
Smart phone users reading text messages and internet pages hold their devices at a closer distance than they would for printed text—which may have important implications for prescribing vision correction, reports a study in the July issue of Optometry and Vision Science, official journal of the American Academy of Optometry. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.
Optometrists should pay attention to the "working distance" at which patients hold their smart phones and perform appropriate testing at those distances, according to the study by Mark Rosenfield and colleagues of SUNY State College of Optometry, New York.
The researchers evaluated viewing distance and font size in smart phone users. While wearing their usual vision correction (glasses or contact lenses), 129 smart phone users were asked to demonstrate how they would hold their device while reading a text message or a typical Internet page.
The researchers then measured the size of the text on the handheld devices. The goal was to find out whether the working distance at which users held their phones was appropriate for the font size on the devices.
The average font size was comparable to that of newspaper print for text
messages, but somewhat smaller for the internet page. The average
working distance for text messages was 36 centimeters (14.2 inches).
This was closer than the typical near working distance of 40 centimeters
(15.7 inches) when reading printed text. The average working distance
when viewing a web page on a smart phone was even shorter: 32
centimeters (12.6 inches).
Holding smart phones at such close distances could place increased
demands on the eye's ability to correct for distance (accommodation) and
coordination between eyes (vergence), compared to the distances
typically used for reading printed text. Over time, this could lead to
symptoms such as eyestrain and headaches.
Typically, optometrists follow a '1, 2, 10' rule when prescribing vision
correction—assuming a working distance of about one foot for cell
phones, two feet for desktop computers, and ten feet for television
viewing. The new study is one of the first to examine the working
distances at which patients use smart phones or other handheld devices.
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The new study suggests that patients tend to use handheld devices at
closer distances compared to printed materials, which could have
important implications for vision correction. Smart phones "may present a
variety of visual demands that are significantly different in terms of
working distances, gaze angle, and text sizes," Rosenfield and coauthors
Further research is needed to investigate eye's response to prolonged
smart phone use. In the meantime, the researchers believe that
optometrists should ask patients in detail about how they use their
handheld devices, and possibly perform further tests at those closer
distances. Especially for older patients, changes in lens design may be
needed to meet the visual demands of smart phones and other new
technology.This article was originally published at www.newswise.com
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