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Moderate corneal astigmatism (0.75 to 2.00 diopters [D]) occurs in approximately 32% of eyes with cataracts.1 Several manufacturers offer toric intraocular lenses (IOLs) to correct moderate astigmatism. One option is the AcrySof toric IOL (Alcon Laboratories Inc, Ft Worth, Texas), which has been established in prior clinical studies.2
Compared with moderate astigmatism, high astigmatism has fewer treatment options and a lower prevalence: approximately 9% of eyes with cataracts have >2.00 D of corneal astigmatism.1 When AcrySof toric IOLs were only available up to a maximum cylinder power of 2.06 D at the corneal plane (model SN60T5), highly astigmatic patients were left with some residual cylinder,2 or adjunctive limbal relaxing incisions.3,4 In 2009, AcrySof models became available in some countries outside of the United States with cylinder powers up to 4.11 D at the corneal plane (models SN60T6, SN60T7, SN60T8, and SN60T9). This study was conducted to analyze the safety and efficacy of these high-cylinder IOLs.
Patients and Methods
Preoperative Assessment and Prophylaxis
Eligible eyes had cataract and symmetric corneal astigmatism 2.25 D by autokeratometry (model KR-8000 Auto Kerato-Refractometer; Topcon, Tokyo, Japan). Eyes with irregular astigmatism, keratoconus, or prior corneal or keratorefractive surgery were excluded. Uncorrected distance visual acuity (UDVA) was recorded. Axial length was determined by immersion ultrasound or the IOLMaster partial coherence interferometry biometer (Carl Zeiss Meditec AG, Jena, Germany). The SRK-T formula was used to determine the necessary spherical IOL power and an online toric IOL calculator (http://www.acrysoftoriccalculator.com) was used to determine the toric IOL model and axis. All cases incorporated the default value of 0.50 D for surgically induced astigmatism. Autokeratometry values were entered into the calculator. One surgeon (G.C.C.) performed two to three calculations for each eye, moving the potential location of the incision to minimize residual astigmatism, as predicted by the online toric calculator (Figure A, available as supplemental material in the PDF version of this article).
Operative Procedures
After receiving sedation and anesthetic drops, patients were seated at the slit-lamp, which was equipped with an angle-measuring reticule (BX 900 Photo Slit-Lamp; Haag-Streit AG, Koeniz, Switzerland). A thin slit was turned to the 0 and 180° marks. The corneal limbus was scratched at these locations with a sterile insulin needle and inked with a...