Eyeworld

EW REFRACTIVE 64 November 2017 by Stefanie Petrou Binder, MD, EyeWorld Contributing Writer mm by evaluating the centroid (magnitude and direction/angle). The SIA appears to be less impactful with this incision size range than previously described when using the centroid analysis versus aver- age magnitude only. Lens constant optimization and surgeon factors continue to be important com- ponents for optimal outcomes to ensure that the spherical equivalent is correct. However, with improving biometry methods and formulas, this may become less critical. Lastly, understanding the concept of how posterior corneal astigmatism may contribute to the total astigmatic picture will help surgeons avoid over- or undercorrections. Posterior corneal astigmatism is essentially a minus lens acting like against-the- rule astigmatism. If eye surgeons only use anterior corneal measure- ments, their calculations will be off, resulting in an overcorrection of half a diopter in with-the-rule patients, and an undercorrection of 0.3 D in against-the-rule patients, Dr. Fram explained. This can be done by using theoretical methods such as newly adjusted toric calculators (with posterior corneal adjustments), T aking the right steps in the astigmatic management of cataract and refractive patients will positively impact patient satisfaction, premium IOL eligibility, and the quality of vision. The key to toric IOL success involves achieving as close to plano as possible with little astigmatic residual error. Anything more than 0.5 D residual cylinder may leave patients symptomatic and potentially less than satisfied. With this sometimes intimidating goal in mind, eye surgeons need to know how to accurately assess the corneal surface and be comfortable with preparing patients for surgery in the event that there is pre-existing corneal pathology. Ocular surface considerations are the first step in assessing a patient for a toric IOL. In a presenta- tion at the 2017 ASCRS•ASOA Sym- posium & Congress, Nicole Fram, MD, Advanced Vision Care, Los Angeles, and clinical instructor of ophthalmology, Stein Eye Institute, University of California, Los Ange- les, shared her pearls for achieving the best visual outcomes. Ocular surface: Is the patient ready for measurements? "The assumption is that we are accu- rately assessing corneal astigmatism preoperatively with our technolo- gy and that the cornea is regular, measurable, and consistent. Howev- er, the ocular surface can interfere with visual outcomes every time," Dr. Fram said. "That is why when examining patients for toric IOL implantation, we spend time evalu- ating the patient's ocular surface and utilize Placido imaging to evaluate ocular surface disease contributions. As many have advocated, it's best to use at least three devices to confirm reliability of axis and magnitude." Dr. Fram, and many others, emphasize that surgeons need to remain vigilant during the slit lamp examination for signs of ocular surface irregularities. Ocular surface disease, including dysfunctional tear syndrome (best assessed prior to giving dilating drops), epithelial basement membrane dystrophy, pterygia, corneal nodules, upper eye lid chalazion, lagophthalmos, and corneal ectasia, can affect keratome- try and radically skew outcomes and biometry readings. "Even the smallest corneal nod- ule in the periphery can affect your central corneal astigmatism," she said. "Sometimes the only way to truly understand the impact is to use Placido imaging. Additionally, even the smallest upper eyelid chalazion can affect astigmatic readings, so remember to flip the eyelid and take a good look to see if you are getting inconsistent readings." Preoperative diagnostics: What is the total corneal power? The next essential step in toric IOL assessments involves surgically induced astigmatism (SIA), preopera- tive measurements, and diagnostics. Surgeons typically estimate SIA con- tribution based on how the average magnitude of the incision size and type (corneal vs. scleral) will poten- tially affect residual astigmatism. Traditionally, SIA has been estimated by evaluating average magnitude. This is then adjusted for in the total astigmatic correction in the preop- erative planning. However, as first described by Holladay et al., vector analysis involves both the magni- tude and direction of the SIA. Koch et al. recently assessed the SIA con- tribution for incision sizes 2.2–2.4 Torics and astigmatism: Striving for exceptional outcomes Slit lamp photograph depicting negative fluorescein "map like" staining pattern with cobalt blue light of a patient with epithelial basement membrane dystrophy Intraoperative photo of a Symfony Toric IOL (Johnson & Johnson Vision) and the use of coaxial illumination to confirm centration of the IOL on the visual axis Source: Nicole Fram, MD continued on page 66

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