This retrospective study reviewed case-records at the Department of Ophthalmology, Shuang Ho hospital, Taiwan. Between October 2015 and December 2016, patients with cataract and coexisting corneal astigmatism between –1.5 and −4.5 D were recommended simultaneous cataract surgery and astigmatism correction. We divided patients into two groups: one group received FLACS with FS-AK, and the other group received standard phacoemulsification with toric IOL implantation.As age and astigmatism type affect accuracy in predicting the outcomes of FS-AK [15], we selected age- and astigmatism type-matched patients who underwent standard phacoemulsification with toric IOL implantation during the same study period in the toric IOL group. The Joint Institutional Review Board Committee of Taipei Medical University approved the study protocol. The study was conducted in accordance with the tenets of the Declaration of Helsinki. All patients underwent a thorough preoperative ophthalmologic assessment, including manifest refraction, best uncorrected visual acuities (UCVA) and best-corrected distant visual acuities (BCVA), noncontact tonometry (NT530P, NIDEK, Gamagori, Japan), slit-lamp, fundus examination, automated keratometry (KR-8900, Topcon, Tokyo, Japan), axial length, biometry (IOLMaster; Carl Zeiss Meditec Inc, Dublin, California, USA), and corneal topography (Keratograph 4; Oculus, Washington, USA). With different postoperative target refraction, the best UCVA was defined as the best uncorrected distance, intermediate or near vision. Patients with severe corneal disorders, irregular astigmatism, subcapsular opacity of the crystalline lens, active ophthalmic disease, anterior or posterior segment disease were excluded.
Surgical techniques
All surgeries were performed by a single surgeon (Y.D.S.) under topical anesthesia with 0.5% proparacaine hydrochloride (Alcon Laboratories Inc, Fort Worth, Texas, USA).
In the FS-AK group, patients were examined before the surgery with head fixed and chin rested on the slit lamp, and two points at 3 and 9 o’clock were marked on the limbus when the patient was sitting upright. Patients were then transferred to a femtosecond laser platform (LENSAR, Orlando, Florida). A pair of AK incisions were placed in the steep meridian, which was determined using a topographic map. The incision depth of AK extended from 100 m above the endothelium to the surface of the epithelium with a 90 degrees side-cut angle. The optical zone diameter was set at 8 mm. The range of angular arc length of AK incision was between 30 degrees and 80 degrees according to the surgeon’s nomogram, which was modified from the December 2011 version of Woodcock LenSx astigmatic nomogram [16]. The suction ring was docked on the patient’s eye and was centered on the pupil center mark. A femtosecond laser was then used to create anterior capsulotomy, lens fragmentation, and AK consecutively. After removal of the docking cone and suction ring, the main incision for phacoemulsification was created at 210 degrees in the right eye and 30 degrees in the left eye by using a 2.2-mm disposable blade (Alcon, Laboratories, Inc., Fort Worth, TX, USA). A paracentesis was created using a microvitreoretinal blade (Alcon, Laboratories, Inc.) 60 degrees apart from the main corneal incision. Phacoemulsification and implantation of a foldable aspheric IOL (TECNIS, Abbott Medical Optics, Inc., Santa Ana, CA, USA) were then performed. At the end of surgery, the pair of keratotomies were dissected with a blunt spatula to ensure full separation of the incisions.
In the toric IOL group, the IOL power and alignment axis were calculated using an online calculator website (https://www.raytrace.rayner.com).Surgically induced astigmatism (SIA) of the main corneal incision was set as 0.25 D. Furthermore, the steep corneal meridian was determined through topography and marked by the surgeon with Neuhann one-step toric marker (ASICO, Illinois, USA) while patients were sitting upright. The main incision and paracentesis were created at the same locations as in the FS-AK group by using a 2.2-mm disposable blade and microvitreoretinal blade, respectively (Alcon Laboratories, Inc.). Standard phacoemulsification was performed using a foldable IOL (T-flex aspheric Toric; Rayner, UK) implanted into the capsular bag through a Monarch II injector with a C-cartridge (Alcon Laboratories, Inc.). Using a residual ophthalmic viscoelastic device, the corrected IOL alignment was verified at the end of surgery. Stromal hydration of the main incision was performed to form an anterior chamber.
Postoperatively, topical eye drops of tobradex suspension, which contained 0.1% dexamethasone and 0.3% tobramycin (Alcon Laboratories Inc.), were prescribed four times a day for 1 month. Postoperative examinations were performed at 1 day, 1 week, 1 month, 3 months, and 6 months after surgery. Postoperative examinations included manifest refraction, UCVA, BCVA, noncontact tonometry, automated keratometry, and topography.
Vector analysis
The astigmatic analysis was performed using the Alpins method [17] to evaluate the effective correction of astigmatism. The target-induced astigmatism (TIA) vector is the planned surgically induced astigmatic change after surgery, which is equivalent to preoperative corneal astigmatism. SIA is the actual surgically induced astigmatic change. The difference vector (DV) is the induced astigmatic change that would enable the initial surgery to achieve its intended goal, which is equivalent to postoperative astigmatism. The magnitude of error (ME) is the arithmetic difference between SIA and TIA. The angle of error (AE) is the angle described by vectors of SIA versus TIA. The correction index (CI) is calculated as the ratio of SIA to TIA. It indicates overcorrection if it is >1 and undercorrection if it is <1. The index of success (IOS) is the ratio of DV to TIA (the ideal value is 0). The flattening index (FI) is the proportion of SIA required to reduce astigmatism at the intended meridian. SAS 9.3 (Cary, NC, USA) was used to perform statistical analyses. A paired t test was used to compare preoperative and postoperative continuous variables. An independent sample t test or Fisher’s exact test were used to compare the data between two groups. P < 0.05 was considered statistically significant.