For low vision specialists and those who consult them
The iPad for people with visual impairment
October 7, 2010Posted by on
About a year ago, I wrote some blog posts about the Sony Reader and the Kindle for people with visual impairment. This was subsequently written up as a letter in the British Journal of Ophthalmology. I’ve also written briefly on iBooks for the iPhone.
Of course, the big new gadget for electronic books is the Apple iPad. I still haven’t bought one (I can’t really imagine what I’d use it for) but several patients I have seen recently really like it as a low vision reading device. I finally had chance to measure some screen parameters on a friend’s iPad yesterday.
The good news is that, unlike the electronic paper based devices, the screen is very high contrast: its maximum luminance is approximately 270 candelas per metre squared, and its minimum is around 0.5 cd/m sq. This means that the maximum Michelson contrast which can be displayed is very nearly 100%: making this a far better option for reading with reduced contrast sensitivity than a newspaper (Michelson contrast around 70%), a paperback book (about 75%) or a electronic paper device such as the Kindle (60%).
Whereas the iBooks application does not support reversed contrast, many third party readers (such as Stanza) will allow contrast to be reversed, so that text can be displayed as white on a black background. This text format is often preferred by people with media opacities, such as those who have cataract or corneal dystrophies, and those who suffer from increased glare (such as people with retinitis pigmentosa). These readers also allow increased text size (the maximum x-height on iBooks is 3.5mm, equivalent to about 2.4M (about two and a half times newsprint).
I have also been surprised by who has used an iPad: even some of those who refuse to use a computer have mastered downloading and reading books on an iPad: and it’s also useful for viewing photographs and web pages with the ‘pinch to enlarge’ touch gesture.
For visually impaired users, I think the iPad certainly beats the competition for now. However, as someone with good contrast sensitivity and visual acuity who likes physical books and newspapers I’m not sure I’ll be buying one yet.