title: Viewing distance and eyestrain symptoms with prolonged viewing of smartphones.
abstract: BACKGROUND
  This paper investigates viewing distances and eyestrain symptoms in young adults reading from a smartphone for 60 minutes.
  
  
  METHODS
  A 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 60 minutes. 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.
  
  
  RESULTS
  Subjects were 18 young adults (mean age: 21.5 ± 3.3 years) with self-reported good health, normal visual acuity and no accommodative or binocular vision disorders. The mean viewing distance while using a smartphone over 60 minutes was 29.2 ± 7.3 cm. The viewing distance was significantly greater during the first, second and fifth 10-minute time periods (30.6 ± 7.2 cm, 29.7 ± 7.3 cm and 28.9 ± 8.5 cm, respectively) than during the final 10-minute time period (27.8 ± 7.7 cm) (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 60 minutes of smartphone use (Wilcoxon, p < 0.05). There was a significant correlation between change in total symptom score and change in viewing distance (ρ = -0.51; p = 0.03). The only single symptom that correlated with a change in viewing distance was 'uncomfortable eyes' (ρ = -0.52, p = 0.03).
  
  
  CONCLUSIONS
  Viewing distances are closer and eyestrain symptoms are greater after reading from a smartphone for 60 minutes. The viewing distances measured were closer than those previously reported in the literature.
authors.affiliation: School of Optometry and Vision Science, The University of New South Wales, Kensington, New South Wales, Australia.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Long
authors.affiliation: School of Optometry and Vision Science, The University of New South Wales, Kensington, New South Wales, Australia.
authors.forename: Rene
authors.initials: R
authors.lastname: Cheung
authors.affiliation: School of Optometry and Vision Science, The University of New South Wales, Kensington, New South Wales, Australia.
authors.forename: Simon
authors.initials: S
authors.lastname: Duong
authors.affiliation: School of Optometry and Vision Science, The University of New South Wales, Kensington, New South Wales, Australia.
authors.forename: Rosemary
authors.initials: R
authors.lastname: Paynter
authors.affiliation: School of Optometry and Vision Science, The University of New South Wales, Kensington, New South Wales, Australia.
authors.forename: Lisa
authors.initials: L
authors.lastname: Asper
mesh_terms: D001248:Asthenopia / Q000209:etiology*; D005260:Female; D006801:Humans; D008297:Male; D000068997:Smartphone; D013997:Time Factors; D055815:Young Adult
keywords: asthenopia; eyestrain; smartphone; viewing distance