The loss of visual capacity in patients with cataract directly affects the patients' quality of life, making it difficult to perform daily activities such as reading and many other important tasks . The surgical treatment of such disease allows the restoration
of vision and the rehabilitation of the patients, enabling their reintegration into society, including the return to some work activities .
It is known that cataract surgery is a millenarian procedure since its first records were dated in the first century, however, it was not always possible to obtain successful results [3-5].
With the desire and the demand of the patients to no longer use corrective lenses, with the advent of premium intraocular lenses and the advances of devices to perform cataract surgeries, surgeons have a greater arsenal in acquiring the aimed result.
As technology continued progressing, in 2001, the femtosecond laser has appeared.
Such instrument, has a very precise manner of functioning, it uses a wavelength of light close to that of infrared light, transforming the energy of the laser into mechanical energy - a mechanism denominated photodisruption. In order to achieve a good performance it is mandatory a good centering of the eye which will be operated. It is worth noting that the cornea must also be transparent so that a satisfactory penetration of the laser occurs and avoids unpleasant surprises [6-8].
The cost-benefit of femtosecond laser in cataract surgery use has been questioned by some scientists for not being clinically superior in some studies when evaluating visual acuity outcomes . For those who advocate for the use of such technology, they argue that because it is a safe instrument that performs crucial steps in cataract surgery that would be executed by the surgeon, it can decrease the rate of complications .
Capsulotomy is precisely done and ideally sized - thus avoiding myopic and hyperopic shifts, and also anterior and posterior capsule opacifications that can be related to the anterior capsulorhexis' size [11-14]. The laser allows self-sealing and multiplanar incisions at the exact locations permitting great results, the optimal depth of the limbal relaxing incisions for reduction of the astigmatism can be achieved , and lens fragmentation with consequent diminution of surgical ultrasound time leading to less endothelial aggression [16-18].
The present study aims to compare the intraoperative complications and results of two different platforms of femtosecond laser-assisted cataract surgery - Catalys and LenSx - performed by the same cataract surgeon.
This retrospective study is in accordance with the ethical standards of clinical and surgical research and was submitted by the ethics institutional review board of the Medical Staff of the Hospital Oftalmologico de Brasilia (HOB), Federal District. This retrospective, non-randomized, comparative study included 579 eyes of 579 patients who underwent femtosecond laser-assisted
cataract surgery in 2017 by two different platforms - Catalys and LenSx . We selected the patients from the 2017 list allowing enough time to achieve a good level of experience in handling the equipments taking into account the learning curve as since 2015 both platforms were already working in our service .
We selected the medical records that contained patients who underwent a complete ophthalmological evaluation on all visits, before and after surgery. The data collected after procedure was from the 30-day visit. The use of postoperative eye drops medication was similar for all patients.
All Femtosecond Laser-assisted cataract surgeries - FLACSs - were performed by either LenSx (Alcon Laboratories, Inc. Fort Worth, TX) or Catalys (Johnson and Johnsons Lab, Inc. Santa Ana, CL) using the same parameters for nucleus treatment: one 5.9 mm diameter cylinder with fragment pattern, 12 μJ of laser energy, spot and layer separation of 20 μm and fragment size of 400 μm. The surgeon performed clear corneal main incision in the steepest axis of the cornea, and arcuate limbal relaxing incisions following standard protocol . Laser capsulotomy had a 4.9 mm diameter. There is no preference between the platforms when executing the laser in the hospital which allows the proper comparison.
All patients were operated by the same surgeon (W.T.H.), who performed continuous circular capsulorhexis and hydrodissection using the viscoelastic soft-shell technique  a combination of higher-viscosity cohesive and lower-viscosity dispersive. Then, phacoemulsification using the karate prechop technique to break the cataract, followed by the cortex's irrigation and aspiration. To end the procedure, the same surgeon implanted the intraocular lens - IOL- in the posterior segment. There was no selection regarding the IOL type.
We included data on time and number of dockings; cumulative dissipated energy (CDE); preoperative and postoperative pachymetry; loss of corneal endothelial cells; corrected distance visual acuity before and after surgery using a logMAR backlit chart at 4 meters (Precision Vision, Woodstock, IL) away from the patient and contrast to 100%; refractive outcomes by calculating the spherical equivalent; surgery-induced astigmatism calculated using the Warren Hill formula available at https://sia-calculator.com/ (accessed in January 31st) and intraoperative complications in patients over the age of 50 years without any eye disease. The classification of the cataract adopted was the LOCS II - Lens Opacity Classification System - because although the LOCS III was validated as a model superior and more accurate compared to the LOCS II, we adopted the latter in the present study because it was compatible with the one used to fill in the medical records .
We included the patients (1) with presence of a senile cataract, (2) who underwent Femtosecond laser-assisted cataract surgery in 2017 in the Hospital Oftalmologico de Brasilia by either Catalys or LenSx platform, (3) over 50 years of age, and (4) with none of the following exclusionary factors: existence of any other pathological and/or neurological condition that could decrease visual acuity, contrast and/or visual field sensitivity, preoperative ophthalmological diseases and complications.Results
We used parametric tests when requiring inferential statistical analyzes, such tests were applied due to the normal distribution of the data. We used the chi-square test (χ2) to compare categorical variables, while the use of ANOVA was necessary to counterweigh quantitative variables.
We chose Chi-Square test when all the cells of the test had values greater than 5, whereas the Fisher's Exact Test when at least one information cell contained a number less than 5. The Microsoft R Open Software version 3.3.2 along with RStudio version 1.0.143 analyzed the selected data.
A total of 579 eyes of 579 patients were evaluated, 353 (61%) belonging to the female gender and 226 (39%) to the male gender. Of the total amount, 329 (56.8%) were submitted to the Femtosecond Catalys Laser, while 250 (43.2%) were submitted to the LenSx Femtosecond Laser. The variables eye, gender, cataract degree, age, chosen diopter, axis of the incision, specular microscopy and pachymetry before surgery is available in table 1. The corrected distance visual acuity - CDVA - before surgery was superior in the LenSx group than in Catalys, however, it was not statistically significant (0.17 vs. 0.21 logMAR, p = 0.188) - demonstrated in table 1. CDVA evaluated after surgery was slightly higher in the LenSx group (Catalys 0.04 vs. LenSx 0.02, p = 0.090), also without statistical significance - shown in table 2.
When evaluating the spherical equivalent and postoperative pachymetry, as well as the astigmatism induced by the surgery, there was no statistically significant difference as displayed in table 2.
When analyzing the difference of pachymetry before and after surgery it was found discrete increase in both groups, Catalys increase of 1.27 μ vs. LenSx 1.46 μ, p = 0.265 (Figure 1). The specific laser complications had a lower index in the LenSx group 11 (3.34%) compared to the Catalys group 13 (5.2%). For a better understanding, the complications were grouped as follows: Incomp. Inc / very limbal - incomplete incision / very limbal - related to the cases that the incisions performed were incomplete and very limbal in relation to the planned; Incomp. Inc. - incomplete incision - for the eyes that the laser did not reach the planned depth when doing the incision; corneal inc. - corneal incision - incision performed more internally than planned; limbal inc. - limbal incision - incision performed more externally than planned; Caps. / Adherence - capsulorhexis / microadherence - when microadhesions were found in the anterior capsule; incomp. Caps. - incomplete capsulotomy - the anterior capsulotomy was started but was not completed; No caps. - no capsulotomy performed; Incomp. Frag - incomplete cataract fragmentation. Figure 2, p = 0.7709. The conjunctival hyperemia was grouped into five categories: Absent - Catalys 3.2% vs. LenSx 2.7% - for the cases that did not evolve with conjunctival hyperemia after laser application. Traits - Catalys 78.0% vs. LenSx 52.6% - for the cases that presented only traces of hyperemia in less than 01 quadrant. Hyperemia in 01 quadrant - Catalys 10.8% vs. LenSx 19.8%. Hyperemia in 02 quadrants - Catalys 7.6% vs. LenSx 20.7%. Hyperemia in 03 quadrants - Catalys 0.4% vs. LenSx 3.3% and finally, in the 04 quadrants only the LenSx group presented hyperemia in 0.9%, p <0.01 - figure 3.
Endothelial cell loss - Catalys 339.43 (14.33%) vs. LenSx 274.18 (11.42%) cells - and cumulative dissipated energy - CDE - (Catalys 3.62 vs. LenSx 3.21) were higher in the Catalys group but not statistically significant - Table 3.Discussion
The amount of times that the interface of the laser is coupled and fitted to the eye reaching the necessary vacuum to perform the laser is called docking. LenSx group patients had less dockings (1.09) compared to the Catalys group (1.17) - p < 0.01. The maximum number of dockings needed to perform the laser in 01 eye in the Catalys group was 5 times, while the maximum amount in the LenSx group was 3 times - figure 4 and table 3. There was statistical difference regarding the time from the beginning of the suction until the end of the procedure between groups, Catalys obtained an average of docking time of 165.92 seconds vs. LenSx 132.79 seconds, p <0.01.
The final sample of the patients that were included in the study has a high degree of similarity, which makes the comparison suitable. There are studies that compare the different platforms despite a smaller sample number  and also studies that show that the use of such pre-surgical technologies is safe [14-17]. The relevance of this article is reflected in the fact of comparing two femtosecond laser platforms by the same cataract surgeon and same technique, thus reducing the bias that different surgeons with different techniques and abilities may present.
When studying the sample, we observed predominance of female patients 61% and of the right eye 51.8%, with no statistical significance. In both groups, the grade of cataract NO2, NC2, C2 and P2 was similar in over 80% of the individuals.
There was a substantial improvement in visual acuity in both groups when assessed prior to the postoperative surgery. After the procedure, visual acuity values with logMAR correction in the Catalys group were 0.04 with spherical equivalent of -0.20 Vs. 0.03 in the LenSx group with spherical equivalent of -0.23, p-value = 0.0903, which happens to be similar to that found in the literature .
The preoperative pachymetry in both groups was very similar, evidencing an important homogeneity of the sample. When comparing the evolution of the corneal thickness after 01 month of the procedure it was noticed a slight increase of its thickness of 1.26 μ Catalys vs. 1.46 μ LenSx with p-value = 0.265, without significance. In the present study, corneal thickness measurements were not compared after 1 week of surgery. Studies point to increased edema in patients who underwent conventional phacoemulsification on the 7-day visit regarding FLACS but this difference also reduces to insignificant levels on the 30-day visit .
Specific laser complications in the LenSx group were more related to capsulotomy, whereas when dealing with the Catalys group they were more related to the incision. This variable did not show superiority among the groups compared by the lack of statistical significance and agreed with published articles . The conjunctival hyperemia after laser application was higher in the LenSx group with statistical significance. Even with the need to perform in vivo studies on the increase of intraocular pressure when the vacuum is established in the eye, there are already studies that demonstrate a higher intraocular pressure increase in patients submitted to FLACS by the LenSx platform and greater discomfort when compared to Catalys, which justifies and agrees with the values presented in the present study [23,26]. When comparing the two groups regarding the amount of endothelial cells lost there was no great disparity, also without statistical significance. Greater losses were observed in the Catalys group with an average of 65 cells lost when compared with the Lensx group. CDE was also higher among patients who received the application of the Catalys laser with p-value = 0.2. These endothelial losses and energy released are still lower than those observed in patients who underwent phacoemulsification without previous application of the technology studied [6,10,27,28]. The amount of dockings required to perform FLACS was higher in the Catalys group as well as the suction time with p-value = 0.0268. The maximum number needed to apply the technology in one eye to patients receiving treatment by Catalys was 5 times vs. 3 for the LenSx group. The LenSx platform has a unique interface that applies suction directly to the cornea that can facilitate its matching and visualization, while the Catalys platform uses a suction cup composed of two interfaces .
In conclusion, patients who were treated by the LenSx Laser presented greater post-procedure redness, but those who had the Catalys laser application required a greater number and time of docking to have their treatment performed.
This study was supported by Hospital Oftalmologico de Brasilia (HOB) and Centro de Estudos Oftalmologicos Renato Ambrosio (CEORA).
Disclosure of potential conflicts of interest
The authors declare no potential conflict of interest.