IMPORTANCE
Visual acuity is the most frequently performed measure of visual
function in clinical practice and most people worldwide living with visual
impairment are living in low- and middle-income countries.
OBJECTIVE
To design and validate a smartphone-based visual acuity test that is
not dependent on familiarity with symbols or letters commonly used in the
English language.
DESIGN, SETTING, AND PARTICIPANTS
Validation study conducted from December 11, 2013, to March 4, 2014,
comparing results from smartphone-based Peek Acuity to Snellen acuity
(clinical normal) charts and the Early Treatment Diabetic Retinopathy Study
(ETDRS) logMAR chart (reference standard). This study was nested within the
6-year follow-up of the Nakuru Eye Disease Cohort in central Kenya and
included 300 adults aged 55 years and older recruited consecutively.
MAIN OUTCOMES AND MEASURES
Outcome measures were monocular logMAR visual acuity scores for each
test: ETDRS chart logMAR, Snellen acuity, and Peek Acuity. Peek Acuity was
compared, in terms of test-retest variability and measurement time, with the
Snellen acuity and ETDRS logMAR charts in participants’ homes and
temporary clinic settings in rural Kenya in 2013 and 2014.
RESULTS
The 95%CI limits for test-retest variability of smartphone
acuity data were ±0.029 logMAR. The mean differences between the
smartphone-based test and the ETDRS chart and the smartphone-based test and
Snellen acuity data were 0.07 (95%CI, 0.05–0.09) and 0.08
(95%CI, 0.06–0.10) logMAR, respectively, indicating that
smartphone-based test acuities agreed well with those of the ETDRS and
Snellen charts. The agreement of Peek Acuity and the ETDRS chart was greater
than the Snellen chart with the ETDRS chart (95%CI,
0.05–0.10; P = .08). The local Kenyan community
health care workers readily accepted the Peek Acuity smartphone test; it
required minimal training and took no longer than the Snellen test (77
seconds vs 82 seconds; 95%CI, 71–84 seconds vs 73–91
seconds, respectively; P = .13).
CONCLUSIONS AND RELEVANCE
The study demonstrated that the Peek Acuity smartphone test is
capable of accurate and repeatable acuity measurements consistent with
published data on the test-retest variability of acuities measured using
5-letter-per-line retroilluminated logMAR charts.