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EWAP WIN 2018 - Sponsored by Carl Zeiss Meditec

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The news magazine of the Asia-Pacific Association of Cataract & Refractive Surgeons Optimizing SMILE APACRS Supplement to EyeWorld Asia-Pacific Winter 2018 Effect of angle kappa on visual outcomes in SMILE T he centration of any refractive surgery is vital, said Jodhbir Mehta, MD, Singapore. Accurate centration reduces photic phenomena such as glare, halos, and induced higher order aberrations that can occur postoperatively. Experience with LASIK, Dr. Mehta said, has shown that accurate centration is achieved by several means—via faster lasers, greater accuracy with smaller spot sizes, and the use of eye trackers. There are also several options for centration: It can be done centering on the pupil, the visual axis, the corneal vertex or the coaxial sight- ed corneal light reflex. Some of these, he said, are easier and more well defined than others. Reference points, axes, angles When centering a refractive proce- dure, it is important to understand the relationship between various reference points, axes, and angles: angle kappa, the angular distance between the visual and pupillary axes; the pupillary axis, a line passing through the center of the pupil perpendicular to the cornea; the visual axis, connecting the fovea with a fixation point, passing the nodal point of angle lambda; angle lambda, the angular distance between the pupillary axis and line of sight; line of sight, the line run- ning through the center of the pupil to a fixation point; the corneal ver- tex, the point of maximum elevation when viewing a target, near the line of sight, reproducible independent of pupil size; and Purkinje images. Dr. Mehta focused on the effect of angle kappa on SMILE outcomes. Considering angle kappa Several corneal topographers currently available provide mea- surements of angle kappa, though surgeons should be aware that some provide them in polar coordi- nates, others in Cartesian coordi- nates; these can be interchanged using appropriate mathematical formulations. In terms of distribution, angle kappa trends smaller in myopic eyes, tending to be larger in the left eye and reducing with age, but varies such that some myopic eyes have no angle kappa and others have negative angle kappa—an important consideration for myopic treatments. One other consideration for surgeons: While docking with the femtosecond laser obviates the need for an eye tracker, this means that centration must be accurate at the time of docking—being based on patient fixation, the docking does not aim for the center of the pupil. Angle kappa and SMILE Studies have looked into basic centration with SMILE, showing it to be comparable to centration with LASIK. However, all studies rely on comparison with topography scans following patient treatment; what surgeons really need to know with regard to centration, Dr. Mehta said, is whether there is something they can do either intraoperative- ly or before treatment to predict whether a procedure will go badly. Dr. Mehta and his colleagues conducted a retrospective study on 164 consecutive eyes to evaluate centration during SMILE, investi- gating the impact on predictability, efficacy, and safety. Correlating outcomes with decentration from the pupillary cen- ter, there was a tendency toward better vision with around 0.2 mm of decentration; visual acuities of 20/20 or better were achieved by 78.6% of eyes with more than 0.2 mm of decentration, compared with only 68.8% in eyes with less than 0.1 mm of decentration and 66.7% in eyes with between 0.1 mm and 0.2 mm of decentration. Correlating outcomes with decentration from the angle kappa, on the other hand, showed that better uncorrected visual acuity was achieved with from 0.4 mm to less than 0.6 mm of decentration. Moreover, all of the patients who had the greatest decentrations of 0.6 mm or above were the pa- tients who had the highest degree of angle kappa preoperatively; pa- tients with large angle kappa preop show a large offset from the pupil center after docking (Figure 1). The surgeon can therefore predict this outcome preoperatively by measuring the angle kappa. Aiming for centration close to the visual axis is supposed to provide the best visual outcomes. The study confirms that SMILE lenticules not centered on the pupil center provide better visual outcomes for patients with large angle kappa. In April 2017, Carl Zeiss Meditec (Jena, Germany) conducted a user meeting in Singapore. More than just a showcase for their latest technologies, the company's user meeting has grown into a venue for peer-to-peer information sharing, where the world's top ophthalmic surgeons come not only to teach, said symposium chair Gerard Sutton, MD, but also to learn. The second symposium of the meeting focused on optimizing SMILE (small incision lenticule extraction) performed with the ZEISS VisuMax femtosecond laser. Sponsored by Carl Zeiss Meditec Jodhbir Mehta, MD, Singapore Figure 1. Patients who had the greatest decentrations were also those who had the highest degree of angle kappa preop. Kappa intercept Decentration from kappa intercept <0.2 0.2 to <0.4 0.4 to <0.6 At least 0.6 Total 0 to < 0.1 5 0 0 0 5 Proportion 23.8% 0.0% 0.0% 0.0% 3.1% 0.1 to < 0.2 7 13 0 0 20 Proportion 33.3% 24.5% 0.0% 0.0% 12.3% 0.2 to < 0.3 6 19 3 0 28 Proportion 28.6% 35.8% 7.1% 00% 17.3% 0.3 to < 0.4 3 13 12 0 28 Proportion 14.3% 24.5% 28.6% 0.0% 17.3% 0.4 to < 0.5 0 8 17 5 30 Proportion 0.0% 15.1% 40.5% 10.9% 18.5% 0.5 to < 0.6 0 0 6 8 14 Proportion 0.0% 0.0% 14.3% 17.4% 8.6% 0.6 to < 0.7 0 0 4 8 12 Proportion 0.0% 0.0% 9.5% 17.4% 7.4% 0.7 to < 0.8 0 0 0 10 10 Proportion 0.0% 0.0% 0.0% 21.7% 6.2% 0.8 and above 0 0 0 15 15 Proportion 0.0% 0.0% 0.0% 32.6% 9.3%

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