The introduction of FLACS technology in ophthalmic market has created a strong debate of actual benefit of applying this advanced technology as a part of premium package for refractive cataract patients. FLACS is a modern surgical technique that tries to gain the benefit of femtosecond laser precision in the creation of corneal wounds, anterior capsulotomy and nuclear fragmentation in phacoemulsification surgery. It is generally accepted that the corneal wounds and capsulotomy created by femtosecond laser have a superior precision and reproducibility that is unmatched by manual methods. The current study tries to assess the impact of this proposed precision on the final visual acuity and refractive outcome as well as changes achieved in both high and low order aberrations.
This superior visual and refractive outcome of FLACS is still until now a hypothesis rather than a true fact. The support of this hypothesis is that FLACS is associated with improved prediction of surgically-induced corneal astigmatism (SIA) and intraocular lens placement. Most existing studies show either no or little improvement in post-operative refraction. Taking the expenses and logistical issues into consideration, comparison between the refractive outcomes of both techniques is a current issue of intense controversy in ophthalmology society.
Both groups achieved a high degree of post-operative spherical equivalent refractive predictability. In the femtosecond group, 68% of patients achieved ≤0.25 D of absolute refractive error compared to 40% in the manual group (p = 0.026). Lawless et al.  found no significant difference in a retrospective consecutive cohort study of 61 eyes that had FLACS and 29 eyes that had manual phacoemulsification. In a comparison of 48 eyes operated on with femtosecond laser technology and 51 eyes operated on manually, these results were supported by similar findings of Miháltz et al. 
Most of studies published in the literature comparing refractive outcomes of FLACS to manual surgery found no statistically significant difference between the surgical methods while some studies found a small statistically significant rather than a clinically significant difference. The sample size of our study is near to many of the other studies in the literature. We were unable to find any difference between the two surgical groups. Therefore, there is little evidence to support the hypothesis that a capsulotomy constructed by femtosecond laser can lead to a more precise effective lens position (ELP).
On the other hand, a Prospective, multicenter, comparative case series showed inferior refractive outcome of FLACS in comparison to conventional surgery . Overall, more than 93% of eyes had a refractive error within 1 D in both groups. This series includes eyes implanted using conventional IOLs as well as toric IOLs. Toric IOLs were significantly more in FLACS cases (47.4% vs. 34.8%; P < 0.0001).
A metanalysis of 14,567 Eyes from 15 randomized controlled trials and 22 observational cohort studies showing no statistically significant difference detected between FLACS and conventional surgery regarding UDVA, CDVA, and MAE (weighted mean difference, − 0.02; 95% CI, − 0.07 to 0.04; P = 0.57). Analysis of safety parameters revealed that there were no statistically significant differences in the incidence of overall complications between FLACS and conventional surgery; however, posterior capsular tears were significantly more common in FLACS versus CPCS (relative risk, 3.73; 95% CI, 1.50–9.25; P = 0.005). The relative small sample number made our study having a small complication rate. Further studies on large scale may be useful to assess various FLACS related complications and their management. FLACS in special situations as in white cataract, Fuchs dystrophy, post radial keratotomy, post keratoplasty, and in congenital cataract will be of a great impact in revealing FLACS potentials.
In this study, the mean SIA was 0.35 ± 0.67 D for the femtosecond laser-constructed corneal wounds and 0.901 ± 0.882 D for the manual keratome (p = 0.015). Femtosecond laser is capable of constructing precise multiplanar wounds that may be more secure against post-operative wound leakage. That may make femtosecond laser improve the prediction of corneal shape and the calculation of toric IOLs in turn. To our knowledge, our study is one of the few studies comparing SIA between femtosecond laser and keratome wounds in the literature.
In our study, a statistically significant reduction in residual refractive astigmatism at 6 months postoperatively was found in both groups. A combined phacoemulsification and a single arcuate keratotomy was performed using the VICTUS femtosecond laser platform in a series of 54 eyes of 54 patients who had mean postoperative SIA of 1.20 ± 0.68 D that is higher than our series .The mean pre- and post-operative astigmatism was - 1.33 ± 0.57 D and - 0.87 ± 0.56 D respectively which is different from FLACS cases in our series that have a pre- and post-operative astigmatism of - 1.06 ± 1.02 D to − 0.64 ± 0.62 D respectively. Our series had less pre- and post-operative astigmatism that may account for the reduced SIA.
In another series of 48 eyes of 41 patients had cataract surgery (20 FLACS and 28 manual cataract surgery) , the mean preoperative corneal astigmatism was 0.81 ± 0.43 D and 0.82 ± 0.52 D for FLACS and conventional surgery groups, respectively. At 3 months after cataract surgery, it was 0.85 ± 0.55 D and 1.03 ± 0.64 D, respectively (p > 0.05). The mean SIA in laser and the manual group at 3 months was 0.60 ± 0.73D and 0.37 ± 0.92 D respectively (p = 0.318). The average post-operative keratometric astigmatism in the femtosecond group was 0.85 ± 0.55D, compared to manual group 1.03 ± 0.64 at 3 months postoperatively (p = 0.332). These finding support well our results of no differences between both groups postoperatively regarding absolute astigmatic error either total clinical or corneal astigmatism.
In our study, both groups showed a statistically significant decrease of total RMS values at 6 months postoperatively compared to preoperative values. There was no statistically difference between both groups postoperatively regarding RMS higher order aberrations. However, RMS total and low order aberrations were statistically significant less in CPCS group when compared to FLACS group 6 months postoperatively. Analysis of selected subtypes of higher order aberrations found postoperatively conventional group had statistically significance better spherical aberrations and trefoil but the difference was of a little clinical significance. The effect of FLACS on ocular aberrations was addressed in many recent studies.
A study of Miháltz et al. , compared internal aberrations and quality of vision in eyes treated with the LenSx femtosecond laser and standard manual phacoemulsification. Capsulotomy with the LenSx induced significantly less internal aberrations as measured by the Optical Path Difference (OPD) scanner (NIDEK Inc., Japan). At all measured cycles per degree, the femtosecond treated eyes had lower values of intraocular vertical tilt and coma aberrations.
In Wang et al.  study, all wavefront measurements increased significantly at 2 months and 2 years (P = 0.007), except spherical aberration (P = 0.150) in a series of 50 eyes operated using the Victus platform. There was no significant difference in higher-order aberrations between 2 months and 2 years postoperatively (P = 0.486). Corneal astigmatism and higher-order aberration measurements were obtained at the 6-mm zone from corneal topography (Nidek OPD-Scan III; Nidek Technologies). In our series, we measured aberrations in an undilated pupil that mimics the physiological baseline of eyes. Also, lower order aberrations were not assessed in this series in contrast to our study.
An insignificant change of the total HOAs was published by another study . The spherical aberration value is significant and slightly more positive due to the flattening of the cornea due to the incision. It has reported an insignificant difference in Postoperative trefoil after 1 month of the surgery-related changes in corneal wave front aberrations were dependent on incision size. It seems that 2 mm was the limit around which no optical changes are induced by cataract surgery in the human cornea.
Mastropasqua et al.  compared functional and morphological outcomes of femtosecond laser clear corneal incision versus manual clear corneal incision during cataract surgery. They stated that there were no statistically significant differences between the two groups regarding corrected distance visual acuity, surgically induced astigmatism, and corneal aberrations. Keratometric astigmatism was significantly lower in the femtosecond laser group at 30 and 180 days postoperatively. Also, femtosecond laser clear corneal incisions showed a better morphology with lower percentage of endothelial and epithelial gaping and endothelial misalignment compared to the manual technique.
Our study has some potential limitations. For new techniques evaluation, randomized control trials (RCT) represents best level of evidence. The reason for lack of randomization in our study is the relatively high cost of FLACS making it only available at private bases on patient demand. The current study is a prospective non-randomized comparative case-control series of FLACS versus conventional cataract surgery. Due to the current cost of FLACS and the lack of necessary research funding and infrastructure for a RCT, this study design was chosen as it represents the next best level of evidence. Furthermore, RCTs are conducted in artificial trial environments with rigid inclusion and exclusion criteria and may not reflect everyday practice. Our post-marketing study could reflect real clinical practice more closely, where clinicians are faced with. Therefore, data from this study have important merits and represent a significant landmark study on refractive outcomes of FLACS.