Luminance is a useful baseline metric to identify sources of glare within a person's field of view.
However, these devices are only suitable for use in situations where sources of glare can be eliminated.
When sources of glare are removed the iPad can provide measurements of distance visual acuity that are indistinguishable from measures using a standard letter chart.
Second, when sources of glare are minimised, the iPad device can provide measures of distance visual acuity that are indistinguishable from measures made using gold standard letter charts.
After the first set of acuity measurements had been made, the iPad was fitted with an antiglare screen (Sentry Anti-Glare Screen Protector, Enki, Atlanta, Georgia, USA) and positioned away from sources of glare.
The implication of these findings is that while the iPad can be used to present acuity charts in situations where sources of glare can be properly controlled, the system is not suitable for testing in uncontrolled environments.
Therefore, in situations where sources of glare can be controlled, the iPad represents a relatively inexpensive, flexible testing platform which can be updated and changed as necessary via a simple software revision.
The Weber contrast of the dark optotypes presented on a light background was 0.95 for the internally illuminated iPad (measured with no sources of glare), 0.85 for the externally illuminated printed ETDRS chart and 0.98 for the internally illuminated Medmont system.
For the measurements made with antiglare strategies in place (measurement set 2), an antiglare screen was fitted to the iPad and the device was positioned on an acuity chart stand so that it was exactly perpendicular to the floor and so that no sources of glare were visible by reflection.
