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Clinical study results of toric IOLs
Existing options for treating patients with astigmatism, such as glasses or contact lenses, peripheral corneal- relaxing incisions (CRIs) and laser treatment, can be patient-dependent, expensive and unpredictable, can lack precision, regress or can have a limited treatment range. The implantation of toric IOLs remains an option for the treatment of astigmatism.
AcrySof toric IOL
The AcrySof toric IOL (Alcon, Fort Worth, Texas) was approved by the U.S. Food and Drug Administration for use in correcting astigmatism during cataract surgery in September 2005. Its platform is similar to that of a one-piece acrylic lens. The IOL has open loops and posterior toricity, and the toric axis marks are on the anterior surface. The overall length of the IOL is 13 mm, with an optic diameter of 6 mm, and a unique edge design creates consistency among the models (SN60T3, SN60T4 and SN60T5). Model SN60T3 has a cylindrical power at the IOL plane of 1.5 D, a correction of approximately 1 D at the corneal plane; model SN60T4 has a cylindrical power at the IOL plane of 2.25 D, a correction of approximately 1.5 D at the corneal plane; and model SN60T5 has a cylindrical power at the IOL plane of 3 D, a correction of approximately 2 D at the corneal plane.
Delivery is through a Monarch II injector (Alcon, Fort Worth, Texas) with a similar technique to that used when implanting a one-piece acrylic lens.
The AcrySof toric IOL has been associated with rotational stability and includes half-diopter steps at the corneal plane. In addition, a calculator is provided that compensates for surgically induced astigmatism and provides a printout of the proper IOL power to use for the given axis of the incision to ensure accuracy.
AcrySof clinical trial
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In the FDA clinical trial, subjects were enrolled by 11 investigators in a randomized prospective multicenter trial. Two hundred fifty-six patients received a toric IOL, model SA60TT (which includes models SN60T3, SN60T4 and SN60T5), in the first eye, while another 261 served as the control group, receiving a one-piece acrylic lens, model SA60AT, in the first eye.1 The only difference between the two models, SA60TT and SA60AT, is the toricity of the lens.
In a small subset of patients who needed toric IOLs bilaterally, 45 patients received the toric IOL bilaterally, model SA60TT, vs. 24 patients serving as the control group and receiving the one-piece acrylic lens bilaterally, model SA60AT. No other surgical correction of astigmatism was permitted during the study.
Rotational stability
The toric IOL displayed rotational stability within the capsular bag. The mean rotation of all AcrySof toric IOL models in the clinical trial was less than 4°. Of the patients who received a toric IOL, 97.6% had IOLs that rotated less than 15°.1 At 1 year postoperatively, 93.8% of the implanted toric IOLs were within +10° of rotation from the measurement taken at the time of surgery.1
Absolute residual refractive cylinder
AcrySof toric IOLs reduced the absolute residual refractive cylinder. Patients were two times more likely to achieve <0.5 D residual refractive cylinder with a toric IOL than with control.1 The mean absolute residual refractive cylinder for patients receiving a toric IOL was approximately 0.6 D vs. nearly 1.25 D for patients receiving the control IOL. At 1 year postoperatively, more than 50% of patients receiving a toric IOL had less than 0.5 D of cylinder, compared to nearly 25% of patients receiving the control IOL.1
Distance vision
Of the patients who received toric IOLs, 92% achieved an uncorrected distance visual acuity of 20/40 or better (Figure 1).1 Sixty-one percent of patients who received a toric IOL in one eye achieved good distance vision without the use of spectacles; 97% of patients who received a toric IOL bilaterally were spectacle independent (Figure 2).1
| Cumulative UCVA at Distance at 1 Year  Figure 1. Ninety-two percent of patients who received a toric IOL in the FDA clinical trial of the AcrySof toric IOL achieved an uncorrected visual acuity at distance of 20/40 or better.1 |
| Bilateral Toric IOL Implant at 6 Months  Figure 2. Spectacle independence for distance vision was achieved by 97% of patients who were implanted with a toric IOL. |
Adverse events
The percentage of patients with subjective posterior capsular opacification was similar between those implanted with the toric IOL and those patients implanted with a one-piece acrylic IOL. At 1 year postoperatively, approximately 65% of patients implanted with a toric IOL reported posterior capsular opacification, compared to approximately 70% of patients in the control group.
Looking at adverse events such as retinal detachment, macular edema and rise in IOP, the percentage of patients reporting adverse events met the FDA requirements (Table). 1
| Adverse Events at 1 Year Compared to FDA Grid Rate  The percentage of patients reporting adverse events met FDA requirements.1 |
Conclusion
Among available methods for treating astigmatism in cataract surgery, the implantation of toric IOLs is an emerging technology that shows promising results. Similar to implanting a one-piece acrylic lens, toric IOLs provide good distance vision and, in many patients, freedom from spectacles for distance vision. A low absolute residual refractive cylinder has been associated with the implantation of toric IOLs, and the safety profile for toric IOLs has been good. As improvements with regard to rotational stability and treatment and cylinder power range are made, toric IOLs will emerge as an effective, safe treatment option for correcting astigmatism during cataract surgery.
Reference
- Product Information. United States Food and Drug Administration; 2005. Available at http://www.fda.gov/cdrh/pdf/p930014s015c.pdf. Last accessed February 5, 2007.
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