Optical quality after cataract surgery gained more and more attention for providing satisfactory visual outcomes[20, 21]. Studies have shown that FLACS produce better clear corneal incision morphology [8], more precise reproducible capsulotomies [9–13], and better IOL centration [11] when compared with conventional PCS. Even with these reported benefits, it still needs to be proven whether FLACS can produce better optical quality than conventional PCS. Cataract surgery can cause macular thickness change. The complication has brought substantial attention to surgeons due to its potential hazard to vision consequence[14, 22]. However, the complication changed optical quality still needs to be investigated. Therefore, we studied optical quality by MTF, SR and distinct macular thickness for the two groups in current study.
In our study, the UCDA and CDVA shown no significance between the two groups preoperatively and postoperatively, the results were consisted with previously studies that FLACS did not yield better visual results[4, 23]. Studies have shown that FLACS produce significant reduction in effective phacoemulsification time[23, 24], reduce ultrasound power and ultrasound time[25]. In the research, our results show that FLACS can reduce CDE but not phacoemulsification time. We speculate the reason is that FLACS can pre-chop the lens nuclear. Elevation or rapid fluctuations in IOP may cause vascular or rhegmatogenous events[26]. In FLACS group, we found postoperative IOP were raised, the results are consisted with previous researches[27, 28]. Researches have shown that cytokines in anterior chamber after FLACS are higher than conventional PSC[29]. Therefore, we hypothesize that the raised IOP may be associated with these cytokines which leading to increased resistance at the trabecular meshwork. Whether the raised IOP after surgery affects the retinal nerve fiber layer (RNFL) and visual field which need long-term follow-up and further research.
To better understand optical quality after FLACS, the MTF and SR were measured. MTF is the ratio between the image contrast of a specific object through the imaging optical system and the contrast of the object itself[15]. In general, the higher the MTF and SR, the better the ocular optical quality. In PCS group, we found there are different between pre-operation and post-operation in SR and MTF. Furthermore, the differences are statistically significant when the spatial frequencies are at 5, 10 and 25 cycles/degree (c/d). In FLACS group, we found there are different between pre-operation and post-operation in SR but not MTF. We speculate whether FLACS increase surgery induced astigmatism(SIA) compared with PCS which result in not difference between pre-operation and post-operation for MTF[30]. Even though, MTF value is undoubtedly an objective and accurate indicator for optical quality evaluation[31], the assessment of optical quality cannot be completed by one single indicator. Other objective and subjective indicators should also be integrated to make an accurate assessment. Therefore, we measured DLI in the two groups. The DLI in PCS group is significantly higher than the FLACS group in the baseline measurement (post-operative).
Then, we future analyzed the preoperative and postoperative macular thickness values in PCS and FLACS group by OCT. CME can be detected at the first week and peaks about 4 weeks after surgery[32]. In our study, macular thicknesses were performed before surgery and post-operation at 1 month. In PCS group, there are different between pre-operation and post-operation in NIMRT, FV and ART, but not in FLACS group. The results are consisted with previous research that the FLACS does not difference in postoperative macular thickness as compared with PCS [32].
In this study, the limitation includes a relatively small number of patients and short follow-up period. The other limitation is that the eyes were not randomized for FLACS group or PCS group. The current results might have selection bias, although there are no different in nuclear density between two groups. The comparison of optical quality between FLACS group and PCS group needs a long-term follow-up and further research. Such as capsular fibrosis and posterior capsular opacification (PCO) may cause optical quality change in the two groups. Whether the increasing IOP after FLACS has an effect on the RNFL also requires further investigation.