In this prospective study spanning 25 months (24 months of ortho-k treatment and 1 month of discontinuation), sequential changes in CBPs were observed. These led to several key findings. First, dynamic changes in CBPs, including decreasing trends in SP-A1, bIOP, and ARTh, were identified during the 24 months of ortho-k treatment. Second, most CBPs, except bIOP and SP-A1, reverted to baseline levels after 1 month but not after 2 weeks of discontinuation. Finally, the difference in the DA ratio or SP-A1 at 2 weeks was independently correlated with axial elongation at 1 and 2 years.
The study identified significant changes in CBPs, including CCT, bIOP, Integr Radius, and ARTh, following 2 weeks of ortho-k treatment. Decreasing trends of the SP-A1, bIOP, and ARTh values were observed during the 2-year ortho-k treatment. A previous 24-month prospective study indicated substantial fluctuations in CBPs within the first week, followed by stability throughout a 2-year follow-up.
20 This stability may be attributed to the rapid adaptability of the epithelial cells that establishes a renewed equilibrium of intercellular forces. However, certain CBPs, such as SSI and ARTh, were not assessed in the previous study
20 despite their demonstrated repeatability for ortho-k users. Additional insights were provided by a 12-month study, which revealed that most CBP changes occurred approximately 6 months after ortho-k lens wear, with the values stabilizing thereafter.
21 In contrast, the current study observed dynamic alterations in CBPs such as SP-A1, bIOP, and ARTh throughout the 2-year ortho-k treatment. The corneal epithelium is the main structure affected by the mechanical forces exerted by ortho-k lenses. However, previous research has indicated that stromal thickness and cell density are also affected, and epithelial changes are more prominent in the central area but stromal changes are more pronounced in the paracentral and peripheral areas.
22–24 Previous study
25 has suggested that stromal thickening may be due to an overnight edematous response. The positive pressure behind the lens may have a “clamping effect” that inhibits overnight central corneal swelling, resulting in gradual residual thickening in the stromal midperiphery.
25 This phenomenon may explain the ongoing changes in certain CBPs during ortho-k treatment.
Regarding discontinuation effects, some studies
26,27 have reported a reversal of corneal topography toward baseline after ortho-k lens cessation. However, one study
28 reported that flat and steep keratometry values remained significantly different from the baseline following 1-month discontinuation after 3-year ortho-k treatment. In our study, keratometry values returned to baseline at 1 month after ortho-k treatment discontinuation (
P = 0.115). Evidence regarding the recovery of CBPs after long-term ortho-k lens treatment is lacking. Our study showed that most CBPs, except bIOP and SP-A1, reverted to baseline values after 1 month but not after 2 weeks of discontinuation. This suggests the responsiveness of the cornea to external stresses induced by ortho-k and subsequent restoration to its original state and affirms the reversibility of the effects of prolonged ortho-k use.
Several studies
19–21,29 have established a link between baseline or post-treatment CBPs and myopia control using ortho-k lenses. Xiang et al.
20 revealed that the maximum deformation amplitude was an independent factor for axial elongation in a 2-year prospective study. In a cross-sectional study, Li et al.
19 showed a smaller ARTh after ortho-k treatment, indicating a better refractive state and slower AL progression, which could predict ortho-k treatment outcomes. Zhang et al.
21 assessed dynamic corneal response parameters across different ages of patients with myopia using ortho-k lenses with the Corvis ST. Their study demonstrated that baseline ARTh and post-treatment CBPs, such as SSI and peak distance with the maximum amount of corneal movement, at 6 months were correlated with 1-year AL growth. The present study aimed to predict axial elongation of the eye using baseline and 2-week CBP values, as well as their 2-week changes. The findings indicated that the difference in the DA ratio or SP-A1 at 2 weeks was independently associated with the 1- and 2-year axial elongation, with a potentially stronger association observed for the DA ratio. A smaller reduction in the DA ratio at 2 weeks appears to be linked to better axial elongation control. These results may guide clinicians to optimize ortho-k treatment, as CBPs assessed with the Corvis ST can play a pivotal role in predicting AL progression.
This study has several limitations. First, the sample in our study was small, which led us to refrain from conducting subgroup analyses to prevent further reducing the sample size. This decision was made to maintain the statistical robustness of the findings. Future studies with larger samples and the ability to conduct subgroup analyses should provide additional insights. Second, our examination focused on dynamic changes in CBPs over 24 months of lens wear, followed by a 1-month discontinuation. More data may be accrued with a longer duration of discontinuation, which could induce an AL rebound effect and not align with the ethical principles of myopia control. Finally, our study predominantly involved Chinese children, and caution should be exercised when generalizing these findings to other ethnic groups and geographical regions. Further multi-ethnic studies are essential to validate the applicability of our results across diverse populations.
In conclusion, our study identified sequential changes in CBPs over 24 months after ortho-k treatment. Most CBPs returned to baseline levels at 1 month after discontinuation following long-term ortho-k treatment. Additionally, changes in the DA ratio or SP-A1 levels at 2 weeks may be linked to axial elongation of the eye at 1 and 2 years. These findings highlight the potential impact of ortho-k on corneal biomechanics and its implications for myopia control.