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Martin Dominik Kündig, Yu-Chi Tai, John R Hayes, James E. Sheedy; Objective and Subjective Measurements of Visual Fatigue Induced by Sustained Onscreen Reading. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1503.
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© 2017 Association for Research in Vision and Ophthalmology.
Prolonged near-distance viewing has long been regarded as the main source of visual fatigue; however, the physiological causes remain unclear. Using within-subject design, this study examined the changes of accommodative (ACC), vergence (VER), and pupillary functions over a long reading time (≈8 hours). We hypothesized that, with increased reading time, visual fatigue would be increased and oculomotor system would be affected.
Thirty-five subjects (normal vision, no history of eyestrain) read from a computer screen at 55 cm for 5 blocks (50-60 min each). Real-time measurements of ACC (Spherical Equivalent Refraction = SER), VER (Vergence, through eye positions recording), and pupil size were recorded. Clinical tests were conducted off-screen at baseline and after each block, including ACC Amplitude (AA), ACC facility, Base-In (BI) break, BI recovery, Base-Out (BO) break, BO recovery and VER facility. A survey with 25 questions was administered at the same time. The total test time was about 8 hours. Mixed model ANOVAs were used to analyze the effect of time (Block) on the objective responses, with baseline measurement (Block 0) as covariant. Subjective symptom ratings were categorized into four latent factors using factor analysis before further analysis.
Significant effect of time was observed on real-time SER (p=0.007), AA (p<0.001) and BI recovery (p = 0.03). Overall, BI recovery and SER decreased (i.e., ACC lag increased) while AA increased as reading continued. No significant effect was observed on other objective measurements. Subjective symptoms were significantly higher (p<0.001) in later blocks for factors of Mental & Physical Fatigue, Eye Discomfort and Text Perception but not for Display Setting (p=0.4).
Previous research has found increased ACC lag and AA associated with ACC insufficiency, which contributes to visual fatigue. The current study found increment in both subjective symptoms and objective measurements of ACC lag and AA over time, consistent with these reports. However, in this study subjects with normal vision reported moderate symptoms when reading with frequent breaks, suggesting reserved capacity even after 7-8 hours of testing. To determine if this leads to lack of significant effect on the pupillary and VCC system, other than BI recovery, further studies are needed to investigate how more severe visual fatigue may affect the ocular system.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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