LED Illuminance, Correlated Color Temperature Affect Asthenopia Symptoms

Light-emitting diode (LED) illuminance and correlated color temperature (CCT) may affect asthenopia during reading, according to a study published in Ophthalmic Physiological Optics. 

Researchers recruited 22 participants (40% women; mean [SD] age, 25.09 [1.65] years) and assigned them a reading task under 8 LED lighting conditions consisting of 4 illuminances (300 lx, 500 lx, 750 lx and 1000 lx) and 4 CCTs (2700 K, 4000 K, 5000 K and 6500 K) for 2 hours per session. Participants reported asthenopia symptoms including inattention, blurred vision, words moving, difficulty focusing, memory difficulties, eye pain, dry eye, eye foreign body sensation, watery eye, headache, sleepiness, dizziness, anxiety and nausea through a non validated questionnaire that used a 5-point Likert scale (0, asymptomatic; 4, severe). Investigators collected tear samples and assessed inflammatory tear cytokine levels and used modulation transfer function to assess retinal image sharpness and contrast. 

According to the report, participants experienced the lowest level of asthenopia symptoms at 500 lx and 4000K lighting. Participants experienced the greatest reduction of tear concentrations of EGF, TGF-α, IL-6, IL-8, MIP-1β, TNF-α, TNF-β and VEGF-A cytokines at this lighting along with improved accommodative amplitude. Participants who read under low illuminance at low CCT (300 lx–2700 K) and high illuminance at high CCT (1000 lx–6500 K) had higher total scores on the subjective questionnaire, indicating more severe symptoms. 

No significant differences were found between groups for blurred vision (P =.46), words moving (P =.19), difficulty focusing (P =.27), memory difficulty (P =.07), eye foreign body sensation (P =.17), watery eye (P =.20), headache (P =.13), sleepiness (P =.50), dizziness (P =.06), anxiety (P =.32) or nausea (P =.66).

“The data showed that despite illumination that was in accordance with ISO standards, asthenopia increased after each reading task,” according to the researchers. “Furthermore, it can be inferred that specific symptoms (i.e., inattention, eye pain and dry eye), as well as all of the tested [optical quality analysis system] parameters and several inflammatory tear cytokines (EGF, TGF-α, IL-6, IL-8, MIP-1β, TNF-α, TNF-β and VEGF-A), may be key indicators of asthenopia.”

Study limitations include a small sample size, population bias, failure to isolate variations in illuminance or CCT as variables affecting asthenopia, and the use of paper, instead of digital, tasks during observation.