Visual Fatigue Not Accurately Assessed By Critical Flicker-Fusion Frequency

Critical flicker-fusion frequency (CFF) does not correlate with visual fatigue symptom questionnaire scores reported by computer users, according to a study published in Ophthalmic and Physiological Optics. These findings suggest that CFF may not be a reliable instrument for assessing visual fatigue. 

Researchers included adults with computer vision syndrome (CVS; N=120) who were enrolled in a previous randomized controlled trial. Participants underwent CFF, near point of convergence, near point of accommodation, saccadic eye movement, blink rate of visual fatigue, and visual fatigue symptom assessment before and after performing a 2-hour computer task. CFF was measured using a 2-interval forced-choice method and participant symptoms were assessed with a validated questionnaire based on a scale from 0 to 100 (0, asymptomatic; 100, severely symptomatic).

Participants were randomized (1:1:1:1) to 1 of 4 cohorts which included spectacle intervention with and without blue light-blocking lenses. These 2 groups were further subdivided into separate cohorts according to clinician advocacy (the clinician did or did not advocate for the efficacy of the intervention). However, all participants were led to believe they were receiving active intervention with a blue light-blocking lens.

Visual fatigue questionnaire scores changed significantly following the computer task (mean change, 92 units; 95% CI, 11-122), while CFF did not demonstrate a significant change (mean change, -0.7 Hz; 95% CI, -1.7-0.3). 

No significant correlation between overall symptom scores and CFF were noted with respect to both the post-task (r=-0.13; 95% CI, -0.31-0.05) or the change from baseline assessments (r=-0.18; 95% CI, -0.35-0.01), according to the report.  

These findings cast doubt on the reliability of CFF for measuring visual fatigue in patients with computer vision syndrome. “Overall, the evidence supporting CFF as a relevant measure of visual fatigue is uncertain, both in terms of theoretical support that CFF actually measures visual fatigue, as well as the magnitude of effects shown experimentally,” the study authors state.

Study limitations include the use of only 1 questionnaire to report subjective symptoms.