Abstract Myopia has become a major global public health problem. Exposure to outdoor light may explain the protective effect of outdoor activities on myopia. Currently, a growing number of studies focus on the effects of the spectrum on eye health. Recent studies have found that violet light may have a protective effect on myopia, but the mechanism of action between violet light and myopia is not yet fully understood. The paper reviews the association between violet light and myopia prevention and control, and the possible mechanisms of violet light and myopia to provide a reference value for further exploration of the role of violet light on myo pia .

Objective: To explore two visual acuity standards for examining uncorrected visual acuity (UCVA) to define poor vision in lower grade elementary school students, and to compare the difference of screening myopia rates when combined with non cycloplegic auto refraction (NCAR), so as to provide a scientific basis for standardizing UCVA examination methods using CAR as the gold standard of authenticity and reliability. Methods: From March 22nd to April 9th, 2023, a total of 549 first and second grade students aged 7-8 years from a primary school in Hefei City were selected for the study by convenient cluster sampling method. Two methods were employed for UCVA examination:the first method involved charts where the student could not make mistakes in identifying at least half of the characters per line (V1), and the second method used charts with character sizes ranging from 4.0 -4.5, 4.6-5.0 and 5.1-5.3, without allowing 1, 2 and 3 errors per line (V2). While NCAR was performed, then 187 students underwent CAR examination. Paired Wilcoxon rank-sum test and McNemar test were used to compare the differences between V1 and V2 methods in defining poor vision and screening myopia rates. Using CAR as the gold standard, the authenticity and reliability of defining screening myopia rates through the combination of V1 and V2 methods along with NCAR were evaluated. Results: The UCVA examination results for V1 and V2 showed statistically significant differences in both the right eye [5.0(4.9,5.0), 4.9(4.8,5.0)] and the left eye [ 5.0 (4.9,5.0), 4.9(4.8,5.0)] ( Z=-13.95, -13.34, P <0.01). The detection rates of poor vision for the right eye were 43.53% for V1 and 63.21% for V2, and the left eye with 44.08% for V1 and 62.11% for V2, with statistically significant differences ( χ 2= 106.01 , 95.09, P <0.01). When screening myopia rates were assessed for UCNA methods combined with NCAR, the right eye rates were 21.49% for V1 and 24.59% for V2, and the left eye rates were 21.31% for V1 and 23.13% for V2, with statistically significant differences ( χ 2=15.06, 8.10, P <0.01). Using CAR as the gold standard, the detection rates in the right eye and left eye were 16.58 % and 17.11%, respectively. The Youden indices for defining screening myopia in the right eye were 0.80 for V1 and 0.79 for V2, and the left eye with 0.85 for V1 and 0.83 for V2. The agreement rates for the right eye were 91.98 % for V1 and 89.30% for V2, and the left eye with 94.12% for V1 and 91.98% for V2. The Kappa values for the right eye were 0.73 for V1 and 0.67 for V2, and the left eye with 0.81 for V1 and 0.75 for V2. Conclusions Authenticity and reliability of two UCVA examination methods combined with NCAR in defining screening myopia are higher in V1 than V2 methods. It is recommended to unify the visual acuity examination methods by requiring the correct identification of more than half of the total number of visual markers in a row.