Comparison of Astigmatism Correction in Cataract Surgery Between Simultaneous Femtosecond Laser-Assisted Intrastromal Arcuate Keratotomy and Toric Intraocular Lens Implantation

To compare the ecacy of astigmatic correction between simultaneous femtosecond laser-assisted intrastromal arcuate keratotomy (AK) combined with femtosecond laser-assisted cataract surgery (FLACS) and toric intraocular lens (IOL) implantation during cataract surgery in moderate astigmatism. Methods We retrospectively reviewed medical records of patients who underwent astigmatic correction via femtosecond laser-assisted intrastromal AK (AK group; 27 eyes of 27 patients) with FLACS or toric IOL implantation (toric IOL group; 21 eyes of 21 patients). All patients had senile cataracts with corneal astigmatism ranging from + 1.00 to + 2.00 diopters (D) before cataract surgery. We measured visual acuity, intraocular pressure, automated keratometry, manifest refraction and topography preoperatively and at 1-day, 1-month, 3-month, and 6-month postoperatively. between femtosecond laser-assisted intrastromal and toric IOL implantation during cataract in


Introduction
A signi cant number of patients undergoing cataract surgery tend to have a varying degree of corneal astigmatism. [1,2] Approximately, a third of cataract patients have more than 1.25 diopters (D) of preexisting corneal astigmatism, whereas approximately 10% have 2.00 D or higher. [1][2][3][4][5][6] The reduction of refractive astigmatism after cataract surgery can result in a signi cant improvement in visual quality, but remaining astigmatisms decrease visual acuity and quality of vision. [7,8] Postoperative astigmatism is an important cause for the lack of achieving emmetropia even after successful cataract surgery. [9,10] Over the past decade, various approaches, including limbal relaxing incisions, corneal incision on the steep axis, astigmatic refractive keratectomy, and toric intraocular lens (IOL) implantation, have been employed to reduce preexisting astigmatism during cataract surgery. [10][11][12] However, limbal relaxing incisions have limitations that include restricted predictability, induced irregular astigmatism, induced ocular aberrations, and abnormal wound healing. [11,12] Excimer laser procedures after cataract surgery are useful for eliminating remaining astigmatism but are rarely used because of high cost and ocular surface problems following excimer laser treatment. [13] Toric IOL implantation during cataract surgery allows better management of astigmatism, leading to better uncorrected visual acuity. [14,15] Recently, femtosecond laser-assisted intrastromal arcuate keratotomy (AK), demonstrating higher precision, safety, and reproducibility in reducing refractive astigmatism, has been suggested as an alternative to these surgical techniques. [16,17] Along with the introduction of femtosecond laser-assisted cataract surgery (FLACS), cataract surgeons could perform femtosecond laser-assisted intrastromal AK during FLACS to reduce corneal astigmatism. [18][19][20][21][22] In the present study, we aim to compare the e cacy of astigmatic correction between femtosecond laser-assisted intrastromal AK and toric IOL implantation during cataract surgery in patients with moderate astigmatism.

Methods
We conducted this retrospective study with the approval of the Institutional Review Board of the Asan Medical Center and the University of Ulsan College of Medicine, Seoul, South Korea (2019 − 1244). The study adhered to the tenets of the Declaration of Helsinki and followed good clinical practice. All patients were informed of risks and bene ts of the surgery and provided written consent for surgery. This retrospective study included 48 patients who underwent cataract surgery by one surgeon (HT) at the cataract and refractive clinic of Asan Medical Center from November 2016 to July 2018. Patients who met the following inclusion criteria were included: older than 18 years, with preexisting corneal astigmatism between + 1.00 and + 2.00 D by simulated keratometry (Sim K) of topography, and agreement of femtosecond laser-assisted intrastromal AK with FLACS or toric IOL implantation during cataract surgery. Patients were excluded from the analyses if they had any optical opacities or pathologies on slit-lamp examination, previous corneal surgeries, ocular trauma, intraocular surgery, severe dry eye, corneal disease, ocular infection, or collagen vascular/autoimmune diseases. Among 48 patients, 27 patients had FLACS and femtosecond laser-assisted intrastromal AK (AK group) and 21 patients underwent conventional cataract surgery with toric IOL implantation (toric IOL group).
All surgeries were performed by one surgeon using topical anesthesia (0.5% proparacaine hydrochloride).
Cataract surgeries were performed with phacoemulsi cation and implantation of a foldable IOL with 2.2 mm limbal incision. The incisions were located at the steep axis of cornea measured by automated keratometry. All non-toric or toric IOLs were injected into the capsular bag. Main incisions were sealed with anterior stromal hydration without corneal sutures. Topical antibiotics and steroid eyedrops were used for 1-month after surgery.
In the AK group, all 27 patients underwent cataract surgery using the Catalys femtosecond laser platform (Abbott Medical Optics, Inc, Santa Ana CA, USA). Horizontal limbal marker was done in sitting position prior to the laser to avoid cyclotorsion. After the patient lies supine, a suction ring with vacuum was aligned with corneal marks, and a safe distance for the docking interface was controlled with a joystick by the surgeon. After surgical site and depth was con rmed using the incorporated optical coherence tomography cross section, anterior capsulotomy and lens fragmentation were performed, followed by the intrastromal AK. The programmed anterior capsulotomy size was 4.8 mm in diameter. Crystalline lens fragmentation was done using a standard template with a pattern described as "lens softening: quadrants" in the system.
Intrastromal AK nomogram of paired symmetric (same length) incisions centered on the steep corneal axis was done, with 8.0 mm in diameter and central 60% of total corneal thickness in depth remaining upper 20% and lower 20% without penetration. The arc length was determined by intrastromal AK nomogram calculator v3, which is provided on the website. The length was proportional to preoperative corneal cylindrical power and was adjusted by the age and type of astigmatism, i.e., against-the-rule, withthe-rule, or oblique astigmatism. Foldable aspheric IOL (TECNIS 1-piece ZCB00 or PCB00 IOL; Abbot Medical Optics, Inc.) was implanted in patients of the AK group. The target of reduction in femtosecond laser-assisted intrastromal AK is corneal astigmatism.
In the toric IOL group, horizontal corneal-limbal marks using a sterile pen was made in each patient, while each was in a sitting position to avoid cyclotorsion. After a patient lied in a supine position in the operating room with aseptic drape, intraoperative markings were made under a surgical microscope with guidance from preoperative horizontal markings. After successful phacoemulsi cation, toric IOL (TECNIS Toric IOL; Abbott Medical Optics, Inc.) was implanted. The goal of toric IOL implantation is to reduce the refractive astigmatism. The appropriate cylindrical power and axis placement of the toric IOL to be implanted were determined with a program available from the IOL manufacturer and the Barrett toric calculator. After the implantation of IOL, IOL alignment and axis were re-checked.
Vector analysis of refractive astigmatism is based on the de nitions and formulas given by Eydelman MB. [23,24] We analyzed the intended refractive correction, surgically induced refractive correction, error ratio, correction ratio, error of magnitude, and error of angle. The intended refractive correction is the vector difference between the preoperative and the target postoperative cylinder vector. Assuming that target refractive state is emmetropia, it is equal to the preoperative astigmatism. The surgically induced refractive correction is de ned as an amount and axis of astigmatism change achieved by surgery. The error ratio is the proportion of the intended correction that was not successfully corrected. The correction ratio is the ratio of the achieved correction magnitude to the targeted correction magnitude; whereas the error of magnitude is the difference in magnitudes between the surgically induced refractive correction and intended refractive correction. Finally, the error of angle is the angular difference between the achieved correction and the intended correction. Double-angle plots of preoperative corneal astigmatism and postoperative refractive astigmatism (3-month and 6-month) are drawn. The double-angle plot tool used in this paper is provided in the American Society of Cataract and Refractive Surgery website. [25] The Mann-Whitney U test, Wilcoxon signed-rank test, and Chi-square test were used for statistical analyses using the SPSS software version 21.0 (SPSS, Inc., Chicago, IL, USA). Differences were considered to be statistically signi cant for P values less than 0.05. Data from automated keratometer and topography were analyzed using vector analysis.
There was no intraoperative complication requiring secondary operation in both groups. In the AK group, no case of corneal ectasia or corneal perforation was occurred. There was no instance of IOL misalignment more than 10° in the toric IOL group.

Discussion
Cataract surgery has evolved into a refractive procedure during which spherical and cylindrical errors are minimized, nally resulting in satisfactory spectacle-free visual outcomes. However, accurate surgical planning and perfect correction of astigmatism have been challenging for cataract surgeons. Many previous studies compared several options during cataract surgery to correct astigmatism, including opposite clear corneal incisions, limbal relaxing incisions, manual AK, and toric IOL implantation. The implantation of toric IOL is considered as an effective surgical option to reduce refractive astigmatism. [14,26,27] Additionally, recently introduced FLACS showed comparable results with conventional cataract surgery.
[28] Furthermore, simultaneous astigmatism correction with femtosecond laser-assisted intrastromal AK combined with FLACS is reported to be adjustable for managing astigmatism in cataract surgery.
[29] To the best of our knowledge, no comparison between femtosecond laser-assisted intrastromal AK and toric IOL implantation in the aspect of astigmatism correction was reported yet. In the present study, we aim to compare the effectiveness of astigmatism reduction in cataract surgery between the two procedures: simultaneous femtosecond laser-assisted intrastromal AK combined with FLACS and toric IOL implantation.
In this study, signi cant correction of refractive astigmatism was derived by both femtosecond laserassisted intrastromal AK and toric IOL implantation. Our previous study suggested that the femtosecond laser-assisted AK following conventional cataract surgery is comparable to implantation of toric IOL in patients with preoperative astigmatism between + 1.00 and + 3.00 D. [19] However, there are some important differences between the current study and our previous study. That is, whereas femtosecond laser-assisted trans-epithelial AK was performed for patients who were not satis ed with their remaining astigmatism, following conventional cataract surgery in our previous study, [19] femtosecond laserassisted intrastromal AK was performed simultaneously with FLACS in patients with lower preexisting astigmatism up to + 2.00 D in the present study. In addition, intrastromal AK was performed in this study, while trans-epithelial AK was done previously. Intrastromal AK with central 60% of total corneal thickness in depth remaining upper 20% and lower 20% without penetration could be safer than trans-epithelial AK which includes Bowman's layer incision followed by anterior stromal in ammation with epithelial hyperplasia.
[30] According to our previous study, in cases of lower magnitude of preoperative astigmatism, there was comparable effect between femtosecond laser-assisted trans-epithelial AK and toric IOL implantation with regards to postoperative astigmatism correction. In the current study, also, comparable astigmatism correction was noted between simultaneous femtosecond laser-assisted intrastromal AK combined with FLACS and toric IOL implantation in terms of refractive astigmatism reduction. Both femtosecond laser-assisted intrastromal AK and toric IOL implantation could effectively reduce refractive astigmatism postoperatively.
By performing femtosecond laser-assisted intrastromal AK during cataract surgery, corneal astigmatism was effectively corrected postoperatively. Signi cant reduction in corneal astigmatism was made in the AK group at all of each postoperative follow-up period. Principle of the toric IOL implantation does not affect corneal astigmatism. However, for the reason that on-axis clear corneal incision may alter postoperative surgically induced astigmatism in cataract surgery, corneal astigmatism as well as refractive astigmatism was also compared between the two groups. Obviously, compared to baseline preoperative levels, the amount of reduction was not signi cant in the toric IOL group, while signi cant reduction of corneal astigmatism was noted in the AK group.
In femtosecond laser-assisted intrastromal AK group, no signi cant change was seen in vector analysis during each follow-up period of 1-month, 3-month, and 6-month postoperatively. In line with our results, previous study reported that the reduced corneal astigmatism after intrastromal AK showed a stable course during 6-month postoperatively.
[16] Reported stability in astigmatism correction could be attributed to the fact that femtosecond laser-assisted intrastromal AK is performed with optical coherence tomography-guided computer software with calculated nomogram. Considering that there was no ocular complication such as corneal ectasia or epithelial ingrowth, albeit short term follow-up period, femtosecond laser-assisted intrastromal AK with FLACS can be an effective, reproducible, and precise alternative procedure not only to remove cataract, but also decrease astigmatism.
With the passage of follow-up period, tendency of undercorrection of astigmatism was noted in the toric IOL group. Surgically induced refractive correction, correction ratio, and error of magnitude was signi cantly changed at 3-month and 6-month postoperatively in the toric IOL group compared to The present study had several limitations, including its retrospective design and relatively short-term follow-up period. A prospective randomized clinical trial study with an appropriate sample size would allow a more thorough comparison with regards to astigmatism correction between the femtosecond laser-assisted intrastromal AK and implantation of toric IOL during cataract surgery.
In conclusion, femtosecond laser-assisted intrastromal AK in FLACS, as well as toric IOL implantation, is a comparable procedure in terms of reducing astigmatism in cataract surgery for patients with moderate astigmatism.  Double-angle plots of preoperative corneal astigmatism and 6-month postoperative refractive astigmatism in patients who underwent femtosecond laser-assisted intrastromal arcuate keratotomy with femtosecond laser-assisted cataract surgery.