In the current study, we observed a changing pattern toward teenager’s myopia, the corneal topographic and biomechanical parameters were significantly different compared with that of initial measurements. Many studies were taken focus on the differences in the values of anterior segment parameters of myopic and emmetropic eyes, or conducted on older individuals. However, the prevalence of myopia is known to vary and high in young age, therefore, it is important evaluating structural changes associated with myopia to develop strategies preventing progression of myopia and its complications.
In the present study, ACD, ACV, ACA, TCT, PD, AL and SE were measured in myopia teenagers and their relationships with refraction, age and gender investigated. Our results showed that age and gender have no difference of included myopia teenagers. Sex has a significant effect on corneal parameters in our study: Boys had higher Rf and Rs, but smaller in K1 and K2 than girls of both anterior and posterior corneal surface. Also, the Anterior chamber volume (ACV) and Axial length (AL) had significant differences between sex. However, there was no difference in ACD of gender, which means boys’ cornea is flatter than girls. Thus, flatted corneas in boys may reduce the prevalence of myopia than girls. Given the significant effects of gender on corneal parameters of myopia teenagers, as shown in this study, we speculate that kid’ behaviors of sex may contribute to the discrepancy across studies. These results highlight the importance of paying different attentions to girls and boys even at the same ages when controlling myopia development. The flatter cornea and deeper anterior chamber would reduce the refractive error. A flatter cornea has lower refractive power and the overall refractive power of the eye will be lower, the light will focus on a point farther from the cornea. Deeper anterior chamber means the distance between the cornea and crystalline lens increases because the summed power of two lens is equal to their sums minus the distance between the lens divided by the index of refraction of the medium. The relationship between the corneal corneal thickness and myopia is contradictory, some reports decline the correlation with corneal thickness and myopia. However, there are some studies report that corneal thickness has positive correlation with myopia. In our results, the correlation was positively, the significant correlation was seen in multiple regression analysis.
In addition to sex, another important finding of this study is age weight on myopia development. As indicated by previous data analysis in Table 1, subjects in 7 to 9 age group increased significantly of Rf and K1 of anterior corneal surface than 13 to 15 age group. Sharply increasingly of corneal shape in the early age indicate 7 to 9 age is the key period of controlling myopia, especially the dream time for Orthokeratology using. Hyman investigate younger baseline age was the strongest factor independently related to faster myopic children, children aged 6 to 7 years have the fastest progression in all age groups. Hiraoka et al follow up 10-years of overnight orthokeratology found thar long-term efficacy and safety of OK lens wear in reducing myopia progression in schoolchildren. Elder children wearing orthokeratology for controlling myopia have weaken effects for the stable of anterior corneal surface development. Q-val of anterior and posterior corneal surface increased significantly without age. However, according to the result of Zhang’s study that coincidence with the current of myopia development. Q-value represents the spherical aberration with positive relation of refractive error. In the emmetropia eyes, central cornea become flatter with age increasing and peripheral cornea grow slowly, while, with the development of myopia in children, with obviously rise of AL and ACD, peripheral cornea become steep followingly. Meanwhile, the PD had increasingly differences in different age groups (P = 0.003, 0.029). The change of PD may have relations with age and refractive degree of myopia. Pupil size has impact on the amount of penetrating light by more peripheral rays penetrating through larger pupils than smaller ones. In some studies, children with larger pupils have less myopia progression than those smaller pupils wearing orthokeratology. This phenomenon may make an explanation of AL prolonged in myopia group. To the best of our knowledge, this is the innovative study to analyze the trend of myopia development in teenagers and the effects of these parameters on myopia. The use of a relatively large sample size of children with a narrow range of SE and age range allowed our study to provide a more detailed examination of whether there are age differences in ocular parameters in teenager than has been performed previously.
Analyses identified corneal parameters as the predominant predictor of teenager’s myopia. The cut point that the trend of myopia in teenagers need to be identified by bio-parameters as objective indicators. This predictive model should enable clinicians and scientists to evaluate the risk for myopia in teenager using simple, feasible measures. As the large number of children with myopia, we should take myopia in teenagers as a usual phenomenon in the development. So, the model should be beneficiated for monitoring teenager’s myopia by optometrists and ophthalmologists to plan children’ eye examination therapy individually. Based on the data analyzed previously, we found the age, Rs, ACD, ACV, AL corelated tightly than other parameters, the cut point of spherical equivalent refractive error for optimized prediction, which is the best predictor of future myopia in teenagers.
There are some limitations of our study. First, our included population was relatively small compared with other studies. Second, a cross-sectional study at one time point, we need a prospective longitudinal study is needed to determine the anatomical changes of myopia in teenagers.