Eyeworld

Supported by unrestricted educational grants from Abbott Medical Optics, Alcon Laboratories, and Bausch + Lomb Impact of rotational error on toric IOL outcomes tools such as excimer lasers and understanding whether to per- form an IOL exchange or rotate the IOL can be very helpful. Conclusion Precise IOL alignment is espe- cially critical when implanting high-powered toric IOLs, but it will be more important with toric multifocal IOLs, which are even more sensitive to residual astigmatism. Dr. Berdahl is in practice at Vance Thompson Vision in Sioux Falls, S.D. He can be contacted at john.berdahl@van- cethompsonvision.com. indicated that rotating the lens 28 degrees clockwise would reduce the astigmatism to less than 1.0 D. During surgery, I looked at the preoperative and intraopera- tive aberrometry measurements, which confirmed that she had approximately 3.0 D astigmatism. After we rotated the IOL 28 de- grees, we repeated intraoperative aberrometry measurements and found that the measured residual astigmatism was less than 0.5 D. One day after we rotated the IOL, she was plano 20/20 and very pleased. Although surgeons may not achieve their target results every time when implanting toric IOLs, time it is with-the-rule astigma- tism. Therefore, estimating pos- terior corneal astigmatism rather than measuring it can result in suboptimal outcomes. Furthermore, the IOL may rotate or it may have been posi- tioned improperly. If the correct IOL is used but it is in the wrong position, I prefer to rotate the IOL. If the incorrect IOL was used, I may perform an IOL exchange or laser vision correction. Tools for correction To guide surgeons in correcting residual astigmatism, David Hardten, MD, and I created the Toric Results Analyzer (astigmatismfix.com). In a large database, we found that in 76% of cases the intended axis will not neutralize the most astigmatism. Moreover, the IOL rotated 70% of the time. There- fore, in 52% of cases both of these problems contribute to residual astigmatism. Figure 1 shows that at 0 degrees of misalignment, vision is crisp and clear with a T9 IOL. If this IOL is misaligned by 15 de- grees, patients have much blurrier vision. If the IOL is misaligned by 1 degree, the patient loses approxi- mately 3.3% of the effective toric power; if it is off by 10 degrees, the patient loses approximately 35% of the toric power (Figure 2). Although this may be less signif- icant with low power lenses such as a T3—resulting in 0.36 D of astigmatism—with high-powered toric IOLs it is a major problem. A T9 corrects 4.11 D at the corneal plane. Therefore, the patient will have almost 1.5 D of residual astigmatism with a 10-degree misalignment. One of our patients re- ceived a T9 IOL and had 3.5 D of astigmatism 1 week after surgery. When we plugged the information into the Toric Results Analyzer at astigmatismfix.com, it Precise IOL alignment is essential for crisp, clear vision, but it is particularly critical with high-powered IOLs W hen correcting astigmatism during cataract surgery, it is easy to reach the 5-yard line. Howev- er, it takes considerable effort to target sources of potential error and consistently reach the end zone. Residual astigmatism There are 3 causes of residual astigmatism after intraocular lens (IOL) implantation: positioning the IOL incorrectly, choosing the incorrect IOL, or implanting the IOL in an eye with severe ocular surface disease, anterior basement membrane dystrophy, or irregular astigmatism. The IOL may be implant- ed in the wrong location or an incorrect IOL may be used if measurements or calculations were performed incorrectly or as a result of unexpected surgically induced astigmatism (SIA). Posterior corneal astigma- tism also plays a role. Roughly 80% of the time this is against- the-rule, but at least 15% of the John Berdahl, MD by John Berdahl, MD 3 Figure 1. Misalignment of a T9 IOL dramatically affects vision. Figure 2. The effects of IOL misalignment on toric correction Misalignment % loss Absolute loss T3 (1.03 D) T9 (4.11 D) 0 degrees 0% 0 D 0 D 5 degrees 17.5% 0.18 D 0.71 D 10 degrees 35% 0.36 D 1.43 D 15 degrees 50% 0.51 D 2.05 D 30 degrees 100% 1.03 D 4.11 D

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