Viewing distance and eyestrain symptoms with prolonged viewing of smartphones

BackgroundThis paper investigates viewing distances and eyestrain symptoms in young adults reading from a smartphone for 60minutes. MethodsA survey related to common asthenopic (eyestrain) symptoms was administered to subjects before and after they read an extract from a novel on a smartphone for 60minutes. Subjects rated their symptoms on a scale from zero (not at all) to four (extremely). The viewing distance to the smartphone was measured on a photograph taken of the subject every minute. Each subject used the same smartphone and read the same text. ResultsSubjects were 18 young adults (mean age: 21.53.3years) with self-reported good health, normal visual acuity and no accommodative or binocular vision disorders. The mean viewing distance while using a smartphone over 60minutes was 29.2 +/- 7.3cm. The viewing distance was significantly greater during the first, second and fifth 10-minute time periods (30.6 +/- 7.2cm, 29.7 +/- 7.3cm and 28.9 +/- 8.5cm, respectively) than during the final 10-minute time period (27.8 +/- 7.7cm) (Wilcoxon, p=0.023, 0.02 and 0.04, respectively). The total symptom score was significantly greater post-experiment (score=8.06) than pre-experiment (score=3.56) (Wilcoxon, p<0.001). Symptoms of tired eyes, uncomfortable eyes and blur increased significantly after 60minutes of smartphone use (Wilcoxon, p<0.05). There was a significant correlation between change in total symptom score and change in viewing distance (=-0.51; p=0.03). The only single symptom that correlated with a change in viewing distance was uncomfortable eyes' (=-0.52, p=0.03). ConclusionViewing distances are closer and eyestrain symptoms are greater after reading from a smartphone for 60minutes. The viewing distances measured were closer than those previously reported in the literature.