A novel experimental setup for induction and objective assessment of visual fatigue

Abstract

Purpose : It is challenging to reliably induce and objectively measure visual fatigue in laboratory settings. This greatly limits the opportunity to test interventions that aim to alleviate or prevent visual fatigue within a short time frame. The purpose of this study was to develop and evaluate a novel experimental setup allowing for a quick induction and continuous measurement of visual fatigue via accommodative microfluctuations (AMFs).

Methods : Forty-three participants (19 to 45 years of age; mean 31.4 ± 6.5 SD) with normal or corrected-to-normal vision were recruited for the purpose of the study. In order to induce visual fatigue, we employed a modified ‘n-back’ task that relied on a rapid presentation of letters (0.2 deg, 20% Weber contrast) in the center of a 7 by 7 array of letters. The participants were asked to keep the changing letters in focus and click whenever a letter “E” appeared 3 spaces in time after another letter “E”. The mean viewing distance was 26.3 cm ± 2.5 SD and it was adjusted according to participants’ accommodation amplitude. Open-field autorefractor Grand Seiko WAM-5500 was used for continuous (20 minutes) measurement of accommodation at 5 Hz during the task. Sliding-window standard deviation of the accommodation data was calculated as an AMFs estimate and a slope of the best linear fit was used as an index of the AMFs change over time. In addition, a subset of 25 participants evaluated their visual fatigue pre and post task subjectively using a questionnaire.

Results : Our task resulted in a significant increase of AMFs over the 20 minutes by approximately 30% (t₄₂ = 3.6, p < 0.001; one sample t-test on the AMF slopes). Furthermore, simulation of different experiment durations revealed that only 12 minutes would be sufficient to achieve measurable increase in AMFs. The objective changes in AMFs were also accompanied by a subjective increase of visual fatigue (t₂₄ = 7.07, p < 0.001).

Conclusions : Our experimental protocol allows for a quick and reliable (12 – 20 minutes) induction of visual fatigue and its objective evaluation. It can be easily implemented to test interventions aiming to alleviate visual fatigue.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.