Eyeworld Supplements

EW APR 2013 - Supported by Abbott Medical Optics Inc.

This is a supplement to EyeWorld Magazine.

Issue link: https://supplements.eyeworld.org/i/322758

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The goal is to leave as little residual refractive cylinder as possible, even if it means flipping the axis T he first key to optimizing outcomes with toric IOLs is patient education. I explain to patients that toric IOLs give them a greater chance of spectacle independence and provide improved vision quality. Most surgeons will agree that a patient who has 2.00 D to 3.00 D of corneal cylinder needs to have a toric; however, surgeons have ques- tions about lower amounts of cylin- der (1.25 D or less). Data have shown that leaving patients with even 0.50 D of cylinder with a monofocal lens will knock their vision down a line, possibly more. If our goal is the best visual acuity, with the least amount of spectacle dependence, then a toric may be appropriate for those lower amounts of cylinder. The key to calculations The actual K values I enter in my toric calculator are from optical biometry. I then use corneal topog- raphy to verify the approximate axis and the magnitude, rather than solely relying on optical biometry. Any device that measures corneal power will have variation, for many reasons. Therefore, when I compare my optical biometry ker- atometry against my corneal topog- raphy, I look for some relationship between the magnitude and the alignment. I like to see the steep axis within 10 degrees to 20 degrees of what I found on optical biometry. I like the magnitude to be in the 15% to 20% range. As we've gotten comfortable with toric calculators, we have seen a number of different benefits. Some of these calculators include the abil- ity to choose among a variety of toric lenses, giving me a residual cylinder and letting me choose whether to maintain the axis of re- fractive cylinder or flip the axis and leave the patient with less net resid- ual cylinder. We need to have a bet- ter understanding of the cylinder correction with effective lens posi- tion, and these calculators allow us to do that. The Tecnis Toric calculator (Abbott Medical Optics, Santa Ana, Calif.) incorporates the Holladay for- mula with the cylindrical correction based on the effective lens position calculated. These formulas have ben- efits, particularly for patients with eyes that are out of normal range. Based on these calculations, I can determine which toric IOL to use and what the residual cylinder is expected to be. Looking at the IOL options, I may choose to flip an axis and leave the patient with less net residual cylinder. It is important to note that flip- ping the refractive axis with a high enough magnitude can be an issue for some patients when prescribing spectacles. However, if I'm faced with a choice between leaving a pa- tient with 0.45 D of refractive cylin- der on the preoperative axis versus flipping him or her to 0.03 D or 0.05 D, at 90 degrees of that original axis, I will flip the axis. The goal is cut- ting down the cylinder. I believe that flipping a small amount and leaving the patient with a smaller amount of residual cylinder is better than leaving him or her with a larger amount at the same axis. Flip- ping the axis with these small values is visually insignificant. My goal is to leave the patient with the least amount of net residual cylinder, and sometimes that requires flipping the axis. With-the-rule versus against-the-rule I almost always operate on the hori- zontal or the 180 degree axis. The location of the steep axis will factor into my IOL selection. For example, if there is 0.5 D of cylinder against- the-rule, my surgically induced astig- matism (SIA) will take care of that. On the other hand, if I have the same amount of with-the-rule astig- matism, with the SIA, I may leave the patient with a net result of approximately 0.75 D of cylinder. For that correction, there is value in using a toric to get that cylinder down to less than 0.5 D. My IOL choices will vary depending on the axis cylinder because I maintain my incision at one position. Preoperative pearls Some of the most important aspects of successful toric IOL implantation occur during the preoperative pe- riod. In addition to our calculations and incisions, another critical aspect is the preoperative/intraoperative marking. I've found that the one- step system basically identifies and marks the steep axis while the pa- tient is sitting in the holding area. This avoids the need to then place a second mark while the patient is lying down. I have gone away from using ink, because ink distorts the precision and the ability to delineate the exact axis for implantation. We 2 by Ike Ahmed, MD Pearls for success with toric IOLs EW San Francisco 2013 Saturday, April 20, 2013 " At the conclusion of the case, keep eye pressures on a more physiologic level, not a very high level. This promotes early adhesion of the capsule to the IOL optic and haptic material. " Ike Ahmed, MD Chart: Intraoperative and postoperative pearls • Use a one-step preoperative/intraoperative marking technique. • Use smaller incisions. • The capsulorhexis should be smaller than the IOL's optic. • At the conclusion of the case, keep eye pressures on a physiologic level. AMO Saturday supplement_SF2013-dl.qxp_Layout 1 4/19/13 11:26 PM Page 2

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