Impact of pupil and defocus ring intersection area on retinal defocus

Purpose: With the rising prevalence of myopia, especially among the young, orthokeratology (Ortho-K) stands out as a promising approach, not only to reduce myopia but also to control the progression of axial length (AL). This study examined how the intersection area between the pupil and defocus ring influenced retinal defocus and axial growth after Ortho-K. Methods: A case-control study was conducted with 100 participants (100 eyes). Both AL and the refraction difference value (RDV), that is, the peripheral refractive error measured with respect to the central value after wearing Ortho-K lenses, were determined. Subjects were categorised into two groups based on the size of the intersection area after 3 months of lens wear: Group A (<4.58 mm(2)) and Group B (>= 4.58 mm(2)). Results: Group B demonstrated significantly lower changes in AL and RDV at 30-40 degrees and 40-53 degrees compared with Group A after 3 months of lens wear (all p < 0.05). After 6 months of lens wear, Group B showed significantly lower changes in AL and RDV in the 40-53 degrees region compared with Group A (all p < 0.05). Correlation analysis revealed that as the intersection area increased, the changes in AL and RDV at 0-53 degrees, 30-40 degrees and 40-53 degrees eccentricity decreased after both 3 and 6 months of lens wear (all p < 0.01). Conclusions: A larger intersection area between the pupil and defocus ring within a certain time period can cause a greater amount of myopic defocus at 30-53 degrees from the fovea. The results suggest that a larger intersection area might lead to more effective control of axial growth.