Eyeworld

EW CORNEA 118 February 2018 Astigmatism continued from page 116 Femto AK in PKP Astigmatic cuts are used for sever- al different indications, including natural astigmatism, post-penetrat- ing keratoplasty (PKP), during and after cataract surgery, and following refractive surgery. In a study that he performed involving the use of AK in 10 eyes of nine patients with pre- vious PKP, Dr. Kohnen reported that preoperative subjective astigmatism went from 7 D to a postoperative subjective astigmatism of 4 D, which was mirrored by the topographic analysis, revealing a change from preoperative topometric astigmatism of 9 D to 6.5 D postoperatively. The spherical equivalent was unchanged in the study eyes while visual acuity improved. "From this study, we learned that for femto AK in cases of PKP, the procedure is safe and easy. You can reduce both topometric and subjective astigmatism. Overall, we have to work on the predictability as there is regression of the effects over time. We need to work on future laser specific nomograms," he said. Safety and efficacy are two good reasons to use the femtosecond laser in placing corneal incisions. Anoth- er reason lies in the fact that the femtosecond laser allows an all-in- one procedure, including the capsu- lotomy, fragmentation, astigmatic surgery, and the incisions. pFLAK In a recent study, penetrating fem- tosecond laser-assisted keratotomy (pFLAK) and laser lens surgery in 27 eyes of 23 patients (aged 65 ± 8 years) with low to moderate total corneal refractive power astigmatism (CATCRP) resulted in a significant reduction of anterior corneal astig- matism (CAANT) and CATCRP but did not affect the posterior corneal curvature significantly, as measured by Scheimpflug photography (Penta- cam HR, Oculus, Wetzlar, Germany). The CAANT of 0.97 ± 0.30 D was significantly reduced to 0.63 ± 0.34 D (P<.001) and the anterior corne- al SIA was 0.7 ± 0.37 D. Posterior corneal astigmatism showed no significant change from preoperative 0.26 ± 0.12 D to postoperative 0.26 ± 0.10 D (P=.625). In line with this finding, the posterior SIA was low at 0.12 ± 0.07 D. Dr. Kohnen noted that the CATCRP showed similar results as CAANT. 1 "In this topographic analysis of anterior, posterior, and total cor- neal refractive power changes after femtosecond laser-assisted keratot- omy, we had success in reducing low amounts of astigmatism with these penetrating laser keratotomies, but will require further research to develop a new, valid nomogram for laser-assisted lens surgery," he said. Femto ISAK The femtosecond laser allows refrac- tive surgeons to effectively create precise, purely intrastromal, arcuate incision patterns as well. According to an interventional case series, intrastromal astigmatic keratoto- my (ISAK) using the femtosecond laser in 16 patients with naturally occurring or post-cataract surgical astigmatism (<3.0 D astigmatism) significantly reduced astigmatism, provided excellent refractive and topographic stability over 6 months, an excellent safety profile, rapid recovery, and visual stability with- out the known risks associated with incisions that penetrate Bowman's membrane. 2 Knowing the surgical factors that influence predictability of SIA outcomes after femtosecond cata- ract surgery can strongly improve outcomes. Corneal biochemical parameters and the astigmatism meridian were independent predic- tors of femtosecond laser intrastro- mal AK efficacy, even after adjusting for AK arc length, AK start depth, and preoperative corneal cylinder, according to outcomes from an unrelated study that included 319 eyes of 213 patients with a mean target induced astigmatism of 1.24 ± 0.44 D, mean SIA of 0.71 ± 0.43 D, and mean difference vector of 0.79 ± 0.41 D. The study used two multiple regression models for SIA prediction, one based on manual limbal relax- ing incision parameters, confirmed age and astigmatism meridian to be associated with SIA in addition to AK arc length, AK start depth, and preoperative cylinder magnitude. The second regression model con- sidered other parameters in addi- tion, and found only lower corneal hysteresis, higher corneal resistance factor, and the astigmatism meridi- an to be independent predictors of greater SIA. 3 "The outcomes of femto AK/ LK depend on a number of factors such as arc width, architecture, depth of incision, radius from the vertex or limbus, axis, and orien- tation," Dr. Kohnen said. "Overall FS-AK is an effective and safe way to correct astigmatism. It provides increased accuracy of incision depth and placement. As nomograms are refined and technologies such as dy- namic OCT are further incorporated into femto systems, results are likely to continue to improve." EW References 1. Löffler F, et al. Tomographic analysis of anterior and posterior and total corneal refractive power changes after femtosecond laser-assisted keratotomy. Am J Ophthalmol. 2017;180:102–109. 2. Rückl T, et al. Femtosecond laser-assisted intrastromal arcuate keratotomy to reduce corneal astigmatism. J Cataract Refract Surg. 2013;39:528–38. 3. Day AC, et al. Predictors of femtosecond laser intrastromal astigmatic keratotomy efficacy for astigmatism management in cataract surgery. J Cataract Refract Surg. 2016;42:251–7. Editors' note: Dr. Kohnen has no finan- cial interests related to his comments. Contact information Kohnen: kohnen@em.uni-frankfurt.de Why I put down my knife: Femto LRI and AK Charles Reilly, MD, has stopped performing bladed LRIs in favor of femto AK and explains the advantages of this approach. EWReplay.org

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