Hand-held smartphones are commonly used for text messaging, e-mail and Internet access. These devices are not only used by adults, but are becoming popular among kids too. In this study, common font sizes in smartphones and the viewing distances in their users were measured. It was found that while font size was comparably equal to newspaper text, the viewing distance in most cases was closer than what is typically maintained while reading text from something like a magazine or newspaper. Such close viewing distances put constraints on the eyes, demanding increased accommodation (the ability of the eye to change its optical power for a better focus) and vergence (eye movement that enables focusing on near and far objects).
Due to extensive use of smartphones these days, it has become important to investigate its effects on the visual health of people using them. The small screens in these smart phones make it necessary to view them from close distances that can affect the eyes’ accommodation and vergence. These effects lead to increased strain on the eyes, causing headaches and discomfort. Previous studies have investigated the working distances in cell phones, desktop computers and televisions, but there is a dearth of studies on the working distance while using smartphone devices. Therefore, this study aimed at measuring the font size and viewing distance in individuals using smart phones.
* Two separate trials were conducted on people using smart phones, while wearing their usual glasses or contacts, to measure the font size and viewing distance.
* The first trial consisted of 129 participants, aged 18 to 39 years, who were asked to display a text message on their smart phone. The vertical height of lower case letters was measured.
* The participants were then asked to hold the device as they normally do while reading a message, and measurements of the distance between their eyes or spectacle plane, and the screen of the smart phone were taken.
* In the second trial, 100 participants, aged 18 to 40 years, viewed a web page from the internet on their smart phone. Text size and working distance was measured as in the first trial.
* The average font size used for text message and viewing the Internet were comparable to newspaper print.
* The average working distance for text messaging and Internet viewing was 36 cm and 32 cm, respectively. This working distance is less than what is usually maintained while viewing text on hard copies.
* The working distance as well as text size was smaller while viewing websites than while typing or viewing a text message.
In this study, authors used only a single measurement of text height per device. Alternatively, measurements of text height by calculating pixels per mm (pixilation density) of the screen and number of pixels per letter height should have been taken. Although pixilation density can be hard to measure as it varies with device, it can help in calculating the height more accurately.
People of all ages are constantly using hand-held electronic devices at working distances closer than required. This exerts unnecessary pressure on the eyes and may result in lowering the eyes’ adjusting capability, causing symptoms such as fatigue, headache, eyestrain, dry eyes, and blurred vision. The present study can be used as a model to further investigate the effect on eyes while using smartphones. The authors of this study suggest that practitioners should “consider the closer distances adopted while viewing material on smartphones when examining patients”, and prescribe the refractive corrections accordingly. Practitioners will also have to keep this under consideration while treating patients with asthenopia (eye fatigue and tiredness), usually associated with nearwork.
For More Information:
Font Size and Viewing Distance of Handheld Smartphones
Publication Journal: Optometry and Vision Science, July 2011
By Yuliya Bababekova; Mark Rosenfield, PhD; State University of New York