Abstract Background The prevalence of myopia is increasing dramatically around the world, and many studies have suggested the possibility that ultraviolet (UV) light is effective to prevent the onset and progression of myopia. However, UV is a risk factor for diseases that cause refractive errors such as cataract and pterygium. In this study, we evaluated the relationship between UV exposure and myopia progression. Methods The dataset consisted of a total of 337 396 eyes of patients in the 12-to-29-year age range, who were prescribed soft contact lenses (SCL) for refractive error at Okada Eye Clinic in Japan between 2002 and 2011. They were tracked over a five-year period and did not change the type of SCL. In this retrospective cohort study based on medical records, we divided patients into two groups, one prescribed SCL with UV protection (UV-SCL), and another prescribed SCL without UV protection (UV + SCL). Results Change in refractive power over five years was measured and results compared. It was −0.413 diopter (D) in the UV-SCL group and −0.462 D in the UV + SCL group. Thus, the progression of myopia was slower in the UV-SCL group. The results were also analyzed separately by gender and degree of myopia at the time of initial prescription, which all showed significant differences (P < 0.001). Conclusion Results suggest that UV exposure may advance myopia. Further research is needed to investigate the underlying mechanisms that could explain this. Results Change in refractive power over five years was measured and results compared. It was −0.413 diopter (D) in the UV-SCL group and −0.462 D in the UV + SCL group. Thus, the progression of myopia was slower in the UV-SCL group. The results were also analyzed separately by gender and degree of myopia at the time of initial prescription, which all showed significant differences ( P < 0.001). Conclusion Results suggest that UV exposure may advance myopia. Further research is needed to investigate the underlying mechanisms that could explain this. Recently, several studies have suggested that spending time outdoors during childhood correlates with the progression of myopia [ 12–15 ]. In a cross-sectional study of 12-year-old children in Sydney, Australia, ( n = 2367) Rose et al . reported that children who spent more total time outdoors had increased hyperopic refraction and a lower prevalence of myopia, whereas children who engaged in high levels of close-up work and low levels of outdoor activity had lower hyperopic refraction [ 16 ]. Although the etiology of myopia is still unknown, some have pointed out that close-up work such as reading is a risk factor [ 17 ]. Furthermore, UV is a risk factor for pterygium (the wing-shaped thickening of the conjunctiva and cornea) and juvenile cortical cataract that affect the conjunctiva and crystalline lens. UV has been shown to cause refractive errors. Therefore, it is questionable whether UV light can really be a protective factor for the progression of myopia [ 22 , 23 ]. Here, a large-scale epidemiological study was conducted on the Japanese population from children to young adults who use soft contact lenses (SCL). The purpose of the study was to clarify the relationship between UV exposure and the progression of myopia by comparing the presence or absence of the UV protection function of SCL. By myopia power at the time of initial prescription, −0.281 D (95% CI= −0.290, −0.272)/−0.323 D (95% CI= −0.333, −0.314) for high myopia, −0.402 D (95% CI= −0.406, −0.398)/−0.435 D (95% CI= Overall, differences in myopia progression between the UV-SCL and UV + SCL groups were observed up to the age of 14 (Fig. 4 , Supplementary Tables S3 – S4 ). Discussion Up to 80% of a person's lifetime UV exposure is reached before the age of 18, so it is recommended that UV-blocking spectacles or contact lenses are worn from a young age [ 23 ]. In the Yokohama study that examined refractive changes over a five-year period in Japanese eyes ( n = 593 273), the largest change was observed in both sexes at the age of 8 years. However, change in myopia decreased with age, and clinical myopia stopped at the age of 27 years in males and 26 years in females [ 24 ]. Furthermore, it has been suggested that UV-blocking contact lenses not only reduce the oxidative damage caused by UV to ocular tissues, but also may delay presbyopia when worn for a long time [ 25 ]. The results of this study showed that myopia progressed in the UV-exposed group. However, there are those who suggest that UV exposure can inhibit the progression of myopia, in particular, studies on violet light (VL: wavelength 360–400 nm), short-wavelength visible violet light that is a component of sunlight [ 20 , 26–30 ]. In a cohort study of Japanese children aged 6 to 12 years and 10 to 15 years ( n = 113, 310), Torii et al . Furthermore, in a study of students in an area of Central Finland ( n = 4305), children who spent a long time indoors had a close reading distance and were at higher risk for myopia [ 41 ]. A study of Spanish children aged 5 to 7 years ( n = 7497) found that myopic children were exposed to more screentime and spent less time outdoors [ 42 ]. However, in a study which considered the prevalence of myopia among people of the same age and ethnicity, the prevalence rate was 3.3% for Chinese Australians aged 6 to 7 years, compared with 29.1% for Chinese Singaporeans of the same age. A further drawback of the study may be that because n was very large, the results may have been overestimated. Since SCL are recommended for use at ages 12 and older, sufficient n was not available for data at age 8, when the change in myopia is greatest [ 24 ]. It should be noted that the difference in average age between UV-SCL and UV + SCL is slightly larger amongst women. In young people, differences in age and gender may have a strong influence on the progression of myopia. In this study, we performed comparisons by age and gender to minimize bias.