This study retrospectively reviewed 100 eyes (60 with monofocal IOL; 40 with toric IOL) of 100 patients who underwent cataract surgery with preoperative corneal astigmatism of >1.5D in Bucheon St. Mary’s Hospital, Bucheon, South Korea from January 2014 to December 2015. It was approved by Institutional review and Ethics Board of Seoul St. Mary's Hospital and we followed all relevant tenets of the Declaration of Helsinki.
The main inclusion criteria were patients who have age- related cataract with corneal astigmatism over 1.5 Diopter.
The study’s exclusion criteria included a history of any ocular disease affecting visual acuity such as infection, trauma, glaucoma, intraocular surgery; a history of retinal disease such as retinal detachment, macular hole, epiretinal membrane, vitreous hemorrhage; an eye with irregular astigmatism such as keratoconus and keratoectasia.
The following were evaluated as part of the preoperative examination: detailed medical history; slit lamp microscopy and fundus examination, distant UCVA and best-corrected visual acuity (BCVA); autorefraction); and corneal topography (Pentacam, Oculus GmBH, Wetzlar, Germany). The axial length used was the mean value determined from two measurements with the IOL Master (Carl Zeiss Meditec Inc., Dublin, CA, USA) twice, and IOL power was calculated using the SRK/T formula. Patients with corneal astigmatism of >1.5 D on both in autorefraction and corneal topography were included as subjects. Implantation of a toric versus monofocal IOL was decided according to the patients’s wishes, after the cost of a toric IOL was explained to them. Patients with irregular astigmatism, pupil size <5.5 mm, retinal abnormalities, and other ophthalmic or systemic diseases that might have affected the corneal topographic mapping or VA were excluded.
Toric and monofocal IOLs
The Tecnis® ZCB IOL (Abbott Medical Optics, Santa Ana, CA, USA) was used as a monofocal IOL, and the Tecnis® ZCT toric IOL (Abbott Medical Optics) as a astigmatic IOL. To determine the IOL power, two values were measured, and averaged, with an Aviso® (Quantel Medical, Clemont-Ferrand, France) and using the ultrasonic bonding method and IOL Master® (Carl Zeiss Meditiec, Jena, Germany) based on the principle of partial coherence interferometry. Measurements were performed by a skilled examiner. IOL power was calculated by setting the target refraction to -3 D using the SRK/T formula. The estimated A-Constants were 118.8 for A-scan and 119.3 for IOL Master. IOL cylinder power and alignment axis were measured using a web-based calculation program (http://www.amoeasy.com/calc), which considers keratometry as well as surgically induced astigmatism, which was set to 0.5.
The patient, once seated, was asked to look straight into the slit lamp microscope, which allowed the calculation of the long-distance fixation point. Reference markers were placed at the 3 and 9 o'clock directions on the corneal limbus using a toric reference corneal marker (AE-2793S, ASICO) just before the surgery. The intended axis of IOL placement was marked on the cornea with a toric axis marker (K3-7910, Katena) with the patient lying down during surgery. All procedures were performed by the same surgeon (Eun Chul Kim), and a 2.75-mm clear corneal incision was made in the direction of the steep axis of astigmatism. Sodium hyaluronate 1.0% (Hyal Plus, LG Life Science, Seoul, Korea) was used for stabilizing anterior chamber. A continuous curvilinear capsulotomy was made using Inamura capsulorhexis forceps (Duckworth & Kent Ltd., Baldock, UK). Hydrodissection and hydrodelineation were performed by a balanced salt solution. Endocapsular phacoemulsification was performed using 2.75-mm-sized phaco-tips and infusion/aspiration cannulas the Infinity Vision System® (Alcon Laboratories Inc., Fort Worth, TX, USA) and OZil™ Torsional Handpiece (Alcon Laboratories Inc.). A clear preloaded IOL (Tecnis® ZCB00 IOL or Tecnis® ZCT toric IOL) was implanted in the capsular bag. The remaining viscoelastic materials behind the IOL were removed after implantation of IOL. In the case of toric IOLs, the IOL axis was rotated until it was positioned parallel to the previously marked. The operation was terminated without corneal suture.
Distance (6.0 m) UCVA and BCVA, auto-refraction, keratometry and slit lamp examinations were performed 1-day, 1-week, 1-month, and 2-months postoperatively. Additionally, 33-cm near-distance UCVA was measured 2 months after surgery. In the group that underwent toric IOL implantation, pupil of patients were dilated to visualize the axis of rotation 2 months post-surgery. All VA values are presented on logMAR units.
Descriptive statistics were calculated as means and standard deviation and a chi-squared test was used to compare categorical variables. The Kolmogorov–Smirnov test was used to test for normality, and the independent t-test was used for intergroup comparisons. A value of P < 0.05 indicated statistical significance. All statistical analyses were performed using SPSS for Windows (v. 24.0, IBM Corporation, Armonk, NY, USA).