To explore the causes for early adjustment of lens parameters in Paragon corneal refractive therapy (CRT) fitting, and analyze the effects of adjustment.

This was a retrospective study. All participants were recruited from patients who were fitted with CRT lenses in the Optometry Center of Peking University People's Hospital from April 2018 to May 2021. The ocular parameters of 65 myopic patients (90 eyes) who met the inclusion criteria were randomly selected. In this study, the adjustment of the parameters was compared and the reason for the adjustment was analyzed. A customized Matlab program was used to calculate the change of treatment zone area (TZA), treatment zone decentration (TZD), and weighted Zernike defocus coefficient (C_{weighted defocus}) after the adjustment. All subjects were divided into three groups according to the causes of adjustments: poor visual acuity group, corneal staining group, and large treatment zone group. Paired t-test was conducted in the overall and each group.

Among all 90 eyes included in the study, the cases of adjustment due to corneal staining accounted for 28 eyes (31%), due to large treatment zone accounted for 41 eyes (46%), due to poor visual acuity accounted for 21 eyes (23%). The variation of sagittal height before and after adjustment of lens parameters in all cases was 6.59±30.85 μm. TZA was 12.88±3.69 mm² and 11.77±3.17 mm² before and after adjustment, with a change of -1.11±3.01 mm² (t=-3.50, P=0.001). TZD was 0.63±0.31 mm and 0.57±0.29 mm before and after adjustment, with a change of -0.07±0.28 mm (t=-2.29, P=0.024). The difference of TZA and TZD was statistically significant between the before and after adjustment. C_{weighted defocus} was 0.44±0.20 D/mm² and 0.49±0.19 D/mm² before and after adjustment, respectively, with a change of 0.03 ± 0.20 D/mm². While the change of C_{weighted defocus} showed no statistically significant difference (t=1.16, P=0.190).

The main reasons for parameter adjustment of CRT lenses were large treatment zone, corneal staining and poor visual acuity. The large treatment zone accounted for the highest proportion. After adjusting the lens parameters, the decentration and the area of treatment zone were reduced.

myopia; orthokeratology; Zernike coefficient; cornea