Abstract:  Objective To compare the difference of digital eye strain between blue-blocking mode and normal mode screen when using for reading task. Design A two-stage cross-designed clinical trial. Participants 74 healthy subjects aged 18~36 years old. Methods The subjects were randomly divided into two groups. 38 subjects (group 1) used normal mode first, and then used blue-blocking mode (400-500 nm 33.9% attenuated) to perform a 40-minute text reading. The second group (36 subjects) performed the task in the reverse order. The corrected visual acuity of the subjects was examined using a standard visual acuity chart. An open-field auto refractor was used to measure the refraction and accommodative lag. The subject's critical flicker frequency (CFF) was measured using a flash fusion frequency meter. These data were recorded within 3 minutes before and after reading. Likert scale was used to record subjective eye strain scores before and after reading. Reading efficiency was defined as a product of reading accuracy and reading rate per minute. Main Outcome Measures Refraction, corrected visual acuity, accommodative lag, critical flicker frequency, eye strain scale score, reading efficiency. Results Using normal mode, the diopter before and after reading was (-0.26±0.47) D and (-0.26±0.49) D, respectively (P=0.742); The accommodative lag before and after reading was (0.94±0.36) D and (1.05±0.42) D, respectively (P=0.002); The corrected visual acuity was 1.04 (1.0, 1.2), 1.03 (1.0, 1.2), respectively (P=0.058); The CFF was (29.03±2.84) Hz and (29.07±3.03) Hz, respectively (P=0.731). The subjective score of eye strain before and after reading was 0.73 (0, 1.00) and 2.04(1.00, 3.00), respectively (P<0.001). The mean value of eye strain score increased after reading, and the difference was statistically significant. Using blue-blocking mode, the diopter before and after reading was (-0.21±0.49) D and (-0.25±0.48) D, respectively (P=0.144), the accommodative lag was (0.98±0.39) D and (1.03±0.43) D, respectively (P=0.109), and the corrected visual acuity was 1.05 (1.0, 1.2), 1.04 (1.0, 1.2), respectively (P=0.096). The critical flicker frequency was (29.06±2.91) Hz and (29.15±3.08) Hz, respectively (P=0.432). The subjective score of eye strain before and after reading was 0.81 (0, 1.00), 1.64 (1.00, 2.00), respectively (P<0.001). The mean value of eye strain score increased after reading, and the difference was statistically significant. Cross analysis were applied for comparing the variation of ocular parameters caused by these two modes and the reading efficiency difference. There were no significant differences in the variations of refraction variation (P=0.447), accommodative lag (P=0.124), corrected visual acuity (P=0.356), CFF (P=0.687), reading efficiency (P=0.817). There was a significant difference for eye strain score (P=0.015) between these two groups. Conclusion Compared with reading using normal mode screen，blue-blocking mode did not cause obvious changes in objective refractive parameters of the human eye, and the subjective digital eye strain is lower for 40 minutes intense concentration text reading. (Ophthalmol CHN, 2023, 32: 299-304)

Key words:  , digital eye strain, blue-blocking