Vector analysis for evaluating the effect of rotation on myopic astigmatism correction after V4c toric collamer lens implantation

Objective  To evaluate the effect of toric collamer lens (TICL) rotation on myopia combined with astigmatism correction after V4c TICL implantation using standardized vector analysis.

Methods  An observational case series study was performed.A total of 152 patients (268 eyes) who underwent V4c TICL implantation for the correction of myopia and myopic astigmatism were enrolled at Henan Eye Hospital from January to December 2021.The preoperative spherical diopter, cylindrical diopter, and spherical equivalent (SE) were -15.00 to -3.25 D, -5.00 to -0.50 D, -16.50 to -3.88 D, respectively.Postoperative TICL vault and axis were measured by anterior segment optical coherence tomography, and postoperative TICL rotation was calculated.Uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), spherical diopter, cylindrical diopter, SE, and target astigmatism vector were recorded before and 1 month after surgery.The effectiveness index, safety index, surgically induced astigmatism vector (SIA), margin of error (ME), absolute value of the difference vector |DV|, correction index (CI), and achievement index (IS) were calculated based on the subjective refraction results 1 month after surgery and the cylindrical axis of the V4c TICL.Vector analysis parameters was compared among patients with different preoperative astigmatism, intraoperative TICL fixation, postoperative TICL rotation, and postoperative vault.The correlation between postoperative TICL rotation and TICL fixed angle deviation, postoperative vault, visual acuity and refraction, and vector analysis parameters were evaluated.This study adhered to the Declaration of Helsinki.The study protocol was approved by the Ethics Committee of Henan Eye Hospital (No.HNEECKY-2021[13]).Written informed consent was obtained from each subject.

Results  At 1 month postoperatively, the mean safety and efficacy indices were 1.27 and 1.29, respectively.There was no statistically significant difference between the predicted SE of (-0.11±0.13)D and the postoperative SE of (-0.07±0.52)D ( t=-0.994, P=0.321).UCVA, BCVA and cylinder diopter in the operative eyes were all improved after surgery compared to before surgery and the differences were statistically significant ( t=17.854, 5.446, -25.634; all P<0.001).The rotation of V4c TICL was 0° to 25°, with a mean of (5.41±4.35)°, which was positively correlated with the V4c TICL fixed angle deviation ( r _s =0.461, P<0.001), negatively correlated with postoperative cylindrical diopter and positively correlated with postoperative UCVA, |DV| and SIA ( r=-0.360, 0.191, 0.205, 0.142; all P<0.05).Vector analysis between groups showed that vault, SIA and |DV| were higher and CI and IS were lower in low astigmatism group than in high astigmatism group ( Z=-3.017, -13.569, -2.793, -2.761, -4.779; all P<0.05).V4c TICL rotation and |DV| were lower in low fixation angle difference group than in high fixation angle difference group ( Z=-7.865, -2.080; both P<0.05).Preoperative cylindrical diopter, intraoperative V4c TICL fixed angle deviation, SIA and |DV| were lower in low rotation group than in high rotation group ( Z=-2.104, -4.578, -2.456, -2.090; all P<0.05).There were no statistically significant differences in the TICL rotation or in each vector between patients with different vault after the surgery (all P>0.05).

Conclusions  V4c TICL implantation can achieve good results for the correction of myopia and myopic astigmatism.There is a slight difference between the fixation axis and the target axis of V4c TICL, which affects the rotation of V4c TICL and |DV|.Postoperative V4c TICL rotation is related to TICL fixed angle deviation, postoperative UCVA, SIA, |DV| and postoperative cylindrical diopter.Postoperative vault has no significant effect on TICL rotation and differences in each vector.

KEYWORDS：