[Long-term prevention and control effects of orthokeratology lenses designed for small treatment zones on children and adolescents with myopia].

Objective: To explore the characteristics of orthokeratology lenses designed for small correction zones and their effectiveness and safety in long-term prevention and control of myopia in children and adolescents. Methods: It was a prospective cohort study that included myopic children and adolescents who received corneal reshaping treatment at the Qingdao Eye Hospital of Shandong First Medical University between January 2019 and May 2020. The patients were randomly divided into two groups using computer-generated randomization, and were fitted with corneal reshaping lenses with small treatment zones and conventional designs, respectively. The uncorrected visual acuity, best-corrected visual acuity, refractive error, and axial length were measured before and after 6, 12, and 18 months of wearing the lenses. Corneal topography with the Pentacam was also performed, and the area and diameter of the corneal treatment zone were calculated using the Matlab software. Results: A total of 60 myopic patients (60 eyes) were enrolled, including 29 males and 31 females, with an age of (10.40±1.01) years and a spherical equivalent of (-2.88±0.42) D. There were 30 cases in the small correction zone group and 30 cases in the conventional group. There was no significant difference in uncorrected visual acuity and spherical equivalent between the two groups at each time point after treatment. The axial growth in the conventional group was (0.16±0.09) mm at 6 months after treatment, (0.28±0.17) mm at 12 months, and (0.37±0.20) mm at 18 months, whereas in the small treatment zone group it was (0.06±0.05) mm, (0.12±0.10) mm, and (0.18±0.14) mm, respectively. The myopia progression rate in the small treatment zone group was only 37.50%, 42.86%, and 48.64% of the conventional group at 6, 12, and 18 months, respectively. Corneal topography showed that the treatment area in the conventional group was (6.98±0.89) mm², while in the small treatment zone group it decreased by 23.2% [(5.36±0.73) mm²] ( P <0.05). Correlation analysis revealed that the axial increase after 18 months of lens wearing was negatively correlated with the age before lens wearing ( P <0.05), positively correlated with the corneal surface treatment zone size ( P <0.05), and not correlated with the pupil diameter and spherical equivalent (all P >0.05). After the shaping treatment, the rate of adverse reaction, which was mild, in both groups was 10%, and the symptoms disappeared. Conclusion: Orthokeratology lenses with smaller treatment zones can significantly reduce the rate of axial length growth in children and adolescents compared to lenses with conventional treatment zones, without compromising treatment safety.