EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/129516
2 Supplement to EyeWorld May 2013 Pearls for success with toric IOLs by Ike Ahmed, MD The goal is to leave as little residual refractive cylinder as possible, even if it means flipping the axis Ike Ahmed, MD " At the of conclusion 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. " 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 questions about lower amounts of cylinder (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 topography 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 keratometry against my corneal topography, 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 ability to choose among a variety of toric lenses, giving me a residual cylinder and letting me choose whether to maintain the axis of refractive cylinder or flip the axis and leave the patient with less net residual cylinder. We need to have a better understanding of the cylinder correction with effective lens position, and these calculators allow us to do that. The Tecnis Toric calculator (Abbott Medical Optics, Santa Ana, Calif.) incorporates the Holladay formula with the cylindrical correction based on the effective lens position calculated. These formulas have benefits, 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 flipping 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 patient with 0.45 D of refractive cylinder 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 cutting 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. Flipping 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 horizontal 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 againstthe-rule, my surgically induced astigmatism (SIA) will take care of that. On the other hand, if I have the same amount of with-the-rule astigmatism, 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 period. In addition to our calculations and incisions, another critical aspect is the preoperative/intraoperative marking. I've found that the onestep system basically identifies and marks the steep axis while the patient 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 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.