Abstract
Technological advances have led to the development of powerful yet portable tablet computers whose touch-screen resolutions now permit the presentation of targets small enough to test the limits of normal visual acuity. Such devices have become ubiquitous in daily life and are moving into the clinical space. However, in order to produce clinically valid tests, it is important to identify the limits imposed by the screen characteristics, such as resolution, brightness uniformity, contrast linearity and the effect of viewing angle. Previously we have conducted such tests on the iPad 3. Here we extend our investigations to 2 other devices and outline a protocol for calibrating such screens, using standardised methods to measure the gamma function, warm up time, screen uniformity and the effects of viewing angle and screen reflections. We demonstrate that all three devices manifest typical gamma functions for voltage and luminance with warm up times of approximately 15 minutes. However, there were differences in homogeneity and reflectance among the displays. We suggest practical means to optimise quality of display for vision testing including screen calibration.
Highlights
Modern portable tablet computers are ideal for home vision testing
Spatial resolution is sufficient for testing visual acuity and the dynamic range of luminance allows a reasonable range of contrasts to be presented
While LCD devices often exhibit an electro-optic response that is better modeled as a sigmoidal function [8], Bala and Sharma (2003) [9] found that many LCD manufacturers build correction tables into the video card that result in LCD responses mimicking the response of a cathode ray tube (CRT), with a power law whose exponent is about 2.0
Summary
Modern portable tablet computers are ideal for home vision testing. They are relatively easy to program and touch-screen functionality allows great versatility. The attraction of the concept is that patients’ visual function may be monitored remotely whilst they remain at home, reducing the number of hospital visits. The possibility of assessing visual function at home has been stimulated by the challenges of an aging population and the increasing socio-economic burden of hospital care. If sufficiently sensitive and specific, the approach should reduce the burden of unnecessary visits for patients. This would have a major impact on patient independence and quality of life [2]
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