The current study showed lower postoperative astigmatism in the VLynk group compared to the Verion group, and was accompanied with more accuracy in the estimated postoperative astigmatism. Moreover, the implantation of toric IOL can contribute to better postoperative refraction status in both the VLynk and Verion groups. On the other hand, longer AL and higher central corneal power led to more residual astigmatism in the population receiving cataract surgery with Verion assistance.
The current study demonstrated more effective astigmatism retardation in the VLynk group compared to the Verion group. In a previous study, the application of VLynk did not result in less residual astigmatism compared to traditional marking method for toric IOL placement. (Solomon et al., 2019) However, the patients recruited in that study were diagnosed with uncomplicated cataract, while the participants included in our study were those with dense nuclear sclerosis cataract or nuclear sclerosis with other lens opacities such as posterior subcapsular opacity or anterior subcapsular opacity.(Solomon et al., 2019) To our knowledge, there are limited studies which demonstrated the effect of astigmatism reduction using the VLynk system in patients with advanced cataract. Moreover, the control group in our current study were patients that received cataract surgery with the Verion system, which can guide the positioning of astigmatism axis intraoperatively and enable more precise axis placement compared to the traditional marking technique during toric IOL implantation.(Panagiotopoulou et al., 2019) In the current study, however, both the residual astigmatism and the difference between estimated residual SE and real residual SE were higher in the Verion group compared to the VLynk group. This finding may indicate the importance of intraoperative refractive measurement in patients whose precise preoperative astigmatism cannot be obtained due to marked lens opacity. Still, whether the refractive measurement of the VLynk system would be affected by corneal disorder like corneal opacity or ectasic condition needs further evaluation.
In this study, the main predictive factor for better astigmatism reduction for patients who received either VLynk- or Verion-assisted cataract surgery were those who had an implantation of toric IOL; it resulted in more effective control of postoperative astigmatism and higher aOR. This result is reasonable, as toric IOL has been an effective method used for astigmatism reduction in cataract surgery for decades.(Chamberlain et al., 2018, Kaur et al., 2017, Keshav and Henderson, 2021, Kessel et al., 2016) In general, implantation of toric IOL was not considered if the amount of preoperative astigmatism was not prominent, which include patients with less than 1 D in our clinic and in previous experiences.(Keshav and Henderson, 2021) Nevertheless, the current study revealed that the patients who received toric IOL implantation had less postoperative astigmatism compared to those who did not implant toric IOL in both the VLynk and Verion groups. This outcome may suggest widening the threshold for toric IOL implantation if advanced guiding systems are available. Additionally, longer AL and higher central corneal power resulted in higher residual astigmatism in the Verion group but not in the VLynk group. Although both the mean AL and mean central corneal power in the Verion group was numerically higher than those in the VLynk group, there was rare evidence that suggest the use of intraoperative aberrometry would benefit such population. We speculate that the multiple measurements procured in the VLynk group contributed to more precise astigmatism prediction. Furthermore, the effect of significant lens opacity may lead to increased preoperative measurement error due to low biometry accuracy. Consequently, multiple measurements, whether with or without the application of VLynk system, is suggested in individuals with higher AL or central corneal power.
Regarding the CDVA, both the VLynk and Verion group reached a mean CDVA non-inferior to 0.8 four weeks after the cataract surgery. The CDVA for both groups in the current study is comparable to those in previous studies.(Chee et al., 2019, Schweitzer et al., 2020) The Verion group showed a numerically lower CDVA compared to the VLynk group, which may be related to the higher ratio of retinal disease in the Verion group. For the patients with retinal disease, approximately half were diagnosed with non-proliferative diabetic retinopathy, while branch retinal venous occlusion and epiretinal membrane comprised the rest. In addition, the rate of glaucoma was also numerically higher in the Verion group compared to the VLynk group. The presence of retinal and glaucomatous disorders may influence the postoperative CDVA to some extent, although it was not statistically significant.
As for the postoperative visual disturbance and complications, 7 patients in the Verion group reported persistent postoperative photic phenomena compared to only one patient in the VLynk group. These differences were not statistically significant, but imply that patient with Verion assistance may be under a higher risk for developing postoperative visual symptom compared to the individuals receiving VLynk assistance. Because the postoperative photic phenomena may influence the quality of life in those who received multifocal IOL implantation and multifocal-toric IOL implantation significantly,(Alio et al., 2017, Hovanesian et al., 2021) VLynk device may be recommended for those with significant lens opacity who require astigmatism correction. As expected, no severe postoperative complications were observed in both groups. Although we did not perform intracameral cefuroxime injection as was suggested in a previous study,(Keating, 2013) the performance of povine iodine swab and perioperative moxifloxacin utilization may also effectively reduce the possibility of postoperative infection.
There are certain limitations in the current study. The small study population with a total of 149 participants may diminish the statistical power of our study. Secondly, the amount of astigmatism in the Verion group was numerically higher than the VLynk group. Although the difference was not statistically significant, it may render some bias to the analysis of residual postoperative astigmatism and the predictive factor for postoperative astigmatism. Also, we did not collect the data for those who received traditional marking technique as another control group for comparison, since this method has been seldom used in our institution for years. Furthermore, higher order aberration should be measured in all the participants since it can also influence patient’s visual satisfaction after cataract surgery;(Ernest et al., 2019) only less than half of our patients received such exam due to the retrospective design of our study. However, since higher order aberration does not significantly influence astigmatism calculation, the analyses of astigmatism in the current study may not be substantially influenced by this oversight.
In conclusion, the application of the VLynk system can contribute to lower postoperative astigmatism and more accuracy in astigmatism prediction compared to Verion assisted cataract surgery in individuals with significant lens opacity. Implantation of toric IOL is effective for reducing the astigmatism in conjuncture with both devices, while the astigmatism retardation is less effective in the Verion system for those with longer AL and higher central corneal power. Consequently, the VLynk system could be recommended for those with obvious lens opacities and astigmatism for better control of postoperative refractive error. Further large scale study to investigate whether the VLynk system can provide good refraction prediction in those with intraoperative complications like posterior capsular rupture may be warranted.