An assessment of the iPad as a testing platform for distance visual acuity in adults

Abstract

Objectives: Visual acuity is a common measurement in general practice, and the advent of new technology such as tablet computers offers a change in the way in which these tests are delivered. The aim of this study was to assess whether measurements of distance visual acuity using LogMAR letter charts displayed on an iPad tablet computer were in agreement with standard clinical tests of visual acuity in adults with normal vision.

Design: Blinded, diagnostic test study.

Setting: Single centre (University) in Auckland, New Zealand.

Participants: University staff and students (n=85). Participants were required to have visual acuity better than 6/60 and wear habitual refractive correction during testing. Participants were excluded if there was any history of ocular pathology.

Primary and secondary outcome measures: Visual acuity measured under a number of conditions.

Results: The iPad tablet with its glossy screen was highly susceptible to glare resulting in acuity measurements that were significantly poorer (approximately 2 LogMAR lines) than those made using an ETDRS chart and a standard computerised testing system (n=56). However, fitting the iPad with an antiglare screen and positioning the device away from sources creating reflected (veiling) glare resulted in acuity measurements that were equivalent those made using gold standard charts (n=29).

Conclusions: Tablet computers are an attractive option for visual acuity measurement due to portability, the ability to randomise letters, automated scoring of acuity and the ability to select from a range of charts. However, these devices are only suitable for use in situations where sources of glare can be eliminated.

Keywords: Biotechnology & Bioinformatics; Ophthalmology.

Figure 1

The visual acuity tests which were used for comparison. The Medmont computerised visual acuity system (top left), the iPad (bottom left), the Bailey Lovie Chart (middle) and the ETDRS letter chart (right).

Figure 2

Visual acuity measurements made using the iPad, printed charts and the Medmont acuity testing system. (A) The effect of glare on the iPad which gave significantly worse acuity measurements than the comparison charts (measurement set 1, n=56). (B) A separate set of measurements made when glare was minimised (measurement set 2, n=29). Under these conditions, the iPad measurements are accurate. (C) Measurements made with glare accounted for and optical defocus in place (measurement set 2, n=29). (D) Measurements made using the paediatric HOTV symbols shown on a printed chart and the iPad (measurement set 2, n=29). The iPad provided accurate measurements when glare was minimised. Errors bars represent 95% CIs.