This is a retrospective cohort study of 44 eyes of 33 patients. The eyes all had corneal astigmatism of 1 to 5 D, and between July 2006 and March 2007 received an AcrySof toric intraocular lens during cataract surgery. Exclusion criteria were axial length of less than 22 mm, zonular weakness, a change in refractive astigmatism of more than 0.5 D within the 3 months prior to surgery, and coexisting maculopathy or glaucoma.
Eyes with a corneal astigmatism (Orbscan, Carl Zeiss, Germany) of less than 1.5 D were implanted with the AcrySof SA60T3 IOL, eyes with a corneal astigmatism between 1.5 D and 2.25D were implanted with the SA60T4 IOL, and eyes showing a corneal astigmatism of more than 2.25 D were implanted with the SA60T5 IOL. A total of 44 eyes of 33 patients were recruited.
Biometry was performed with the IOL Master (Carl Zeiss, Germany), using the Haigis formula for the IOL power calculation and the company's recommended A-constant of 118.4 for the toric IOL. The target postoperative spherical equivalent was aimed to emmetropia.
Preoperatively, the steepest axis of the corneal astigmatism, determined by Orbscan topography was marked at the corneal limbus with a marker pen, using an angle measuring eyepiece on a BQ900 slit lamp (Haag Streit, Switzerland). Cataract surgery was performed by a single surgeon (EH) at the Vista Klinik, Binningen, Switzerland under topical local anesthesia. Each patient underwent the same technique with a 2.8 mm superior clear limbal incision, continuous curvilinear capsulorhexis, phacoemulsification with cleaver technique and bimanual irrigation/aspiration. The toric IOL was implanted into the capsular bag with a Monarch II injector and a B-Cartridge. Subsequently, the IOL was rotated with a second instrument, so that the cylindrical axis of the lens was aligned with the limbal marks of the corneal astigmatism. All patients were prescribed a combination of tobramicin and dexamethasone eye drops 4 times daily for 4 weeks.
At 1 week and 3 months postoperatively all patients underwent best-corrected distance visual acuity, subjective refraction and slit lamp examination. The postoperative corneal astigmatism was assessed by Orbscan topography at 3 months.
For the measurement of the axis of the toric lens the pupil was dilated to enable the peripheral dots on the optic to become visible. A specially designed eyepiece, replacing one of the 10× eyepieces, was inserted in the slit lamp. Looking through the eyepiece, a spirit level, a horizontal line, a black measurement line and a circular scale in the periphery with single degree steps could be seen. With the spirit level the horizontal line could be adjusted to the horizontal axis. A virtual reference line was used, formed by the line between the pupils of patient's eyes, to provide a patient's reference. This reference line was aligned with the horizontal line of the eyepiece at each follow-up to guarantee reproducible measuring conditions. The black measurement line then could be rotated into the axis of the toric IOL. The angle between the black measurement line and the horizontal line represented the angle of the toric IOL. The angle could be read on the peripheral scale in degrees.
Statistical analysis was performed using SPSS Software (SPSS Inc., Chicago, IL, USA). For comparative statistics the Wilcoxon matched-pairs test was used and for independent samples and the Mann-Whitney U-test was used. For association statistics the Spearman rank correlation test was applied. P-values less than 0.05 were considered statistically significant.