Effect of peripheral plus ring diameter and its relationship with pupil diameter on axial elongation in myopic patients after wearing orthokeratology lenses

Objective

To investigate the effect of peripheral plus ring size and its potential associations with pupil diameter (PD) on axial length (AL) elongation in myopic patients after wearing orthokeratology lenses.

Methods

A case-control study was conducted.One hundred eyes from 100 myopic patients who underwent orthokeratolokgy lenses fitting were enrolled at Beijing Ming Vision and Ophthalmology from January to June 2020.AL and central corneal thickness (CCT) measurements were obtained using Lenstar LS900 ocular biometry, and steep keratometry (Ks), flat keratometry (Kf) were assessed using the TMS-4 corneal topographer.The patients were divided into larger peripheral plus ring diameter (LPPRD) group consisting of 55 eyes with PD<PPRD-0.9 mm and smaller PPRD (SPPRD) group consisting of 45 eyes with PPRD-0.9 mm <PD<PPRD+ 0.9 mm based on PPRD and PD sizes in the tangential difference map.Differences in the above parameters before and after wearing orthokeratology lenses were compared between the two groups.The study followed the Declaration of Helsinki.The study protocol was approved by the Ethics Committee of Ineye Hospital of Chengdu University of Traditional Chinese Medicine (No.2021yh-008). All the subjects and their guardians understood the purpose and method of the study and signed the informed consent voluntarily.

Results

The PPRD of LPPRD group was (5.15±0.37)mm 12 months after wearing orthokeratology lenses, which was significantly higher than (4.75±0.32)mm of SPPRD group (t=0.214, P<0.01). The elongation of AL at 3, 6, 9 and 12 months after wearing orthokeratology lenses were (0.13±0.07), (0.23±0.11), (0.31±0.13) and (0.36±0.41)mm in LPPRD group, and (0.06±0.05), (0.11±0.06), (0.14±0.07) and (0.17±0.08)mm in SPPRD group, respectively.There were significant differences in AL elongation at different time points after wearing orthokeratology lenses between the two groups (F_group=30.527, P<0.01; F_time=16.528, P<0.01), and the AL elongation at different time points was smaller in SPPRD group than in LPPRD group, showing statistically significant differences (all at P<0.01). Compared to before wearing orthokeratology lenses, Ks and Kf were significantly smaller and CCT was thinner 3, 6, 9, and 12 months after wearing orthokeratology lenses in both groups (all at P<0.01). There was no significant difference in Ks, Kf, and CCT between the two groups (all at P>0.05). There was no significant difference in PD at different time points before and after wearing orthokeratology lenses between the two groups (F_group=1.133, P=0.293; F_time=231.427, P=0.112).

Conclusions

The size of peripheral plus ring and its relationship with PD are key factors influencing the AL elongation rate in myopic patients after wearing orthokeratology lenses.With smaller PPRD, patients have slower AL elongation and better myopia control.

Myopia; Therapy; Orthokeratologic procedures; Peripheral plus ring; Axial length; Myopia defocus