Changes in Lens Thickness and Power Before and After Myopia Onset.

Purpose: To investigate changes in the crystalline lens before and after the onset of myopia. Methods: This prospective cohort study was conducted in Guangzhou, Guangdong, China. Participants were initially emmetropic or hyperopic at baseline and were followed for 5 years, during which they were categorized into two groups: those who developed myopia (newly developed myopes [NDM]; n = 1669) and those who remained hyperopic or emmetropic (persistent nonmyopes [PNM]; n = 4259). Changes in spherical equivalent refraction (SER), axial length, lens thickness, and lens power were analyzed from 5 years before to 4 years after myopia onset. Age-related trends in SER and biometric parameters were compared between the PNM and NDM groups. Results: The mean age of the included children at baseline was 7.61 ± 2.68 years (range, 3-14 years), with 3272 boys (55.20%). Compared with the PNM group, the NDM group exhibited a faster myopic refraction shift, accelerated axial elongation, and a more rapid reduction in lens thickness and power. Changes in SER and axial length peaked at 1 year before myopia onset (P < 0.001), but lens thickness and power remained relatively stable before myopia onset. The rate of change in SER and biometric parameters all slowed after myopia onset. In the PNM group, lens thickness decreased before age 11 and increased thereafter, whereas lens power decreased continuously, with a slower rate of decline after 11 years of age. Conclusions: SER and axial length demonstrate accelerated changes 1 year before myopia onset, whereas lens thickness and power remain largely stable before and after myopia onset, with changes primarily associated with age.