Eyeworld

EW CATARACT 86 March 2015 by David A. Salz, MD important part of the residency training program at Wills Eye Hospi- tal in Philadelphia. This year, all of our graduating residents will leave the program certified to perform la- ser-assisted cataract surgery (LACS). ISAK study Our goal was to enroll 50 subjects in this prospective, non-randomized study. We enrolled subjects with preoperative astigmatism of 0.5 D to 3.0 D undergoing routine cataract surgery, excluding those with irreg- ular astigmatism, corneal pathology, and any operative or postoperative complications that would severely limit vision. Preoperatively, a slit lamp ex- amination and dilated fundoscopic exam were performed. Astigmatism was measured preoperatively and at 1 and 6 months with manual keratometry, IOLMaster (Carl Zeiss Meditec, Jena, Germany), and cor- neal topography. Refraction was also performed at 1 and 6 months post cataract extraction. All subjects had capsuloto- my, lens fragmentation, and ISAK performed with the Catalys femto- second laser (Abbott Medical Optics, Abbott Park, Ill.), followed by cata- ract extraction and implantation of a monofocal or multifocal IOL. The laser was set to create the intrastromal incisions at a depth Intrastromal arcuate incisions Study shows that using the femtosecond laser to correct astigmatism intrastromally offers greater precision than manual techniques T he majority of patients presenting for cataract surgery have at least some corneal astigmatism, and 41% of them have visually significant astigmatism ≥0.75 D. 1 To achieve optimal distance vision, we want to correct that astigmatism at the time of cataract surgery, either with a toric IOL, limbal relaxing incisions (LRI), or astigmatic keratot- omy (AK). LRIs and AK have been partic- ularly useful to correct astigmatism in patients implanted with multi- focal IOLs. However, with manual techniques it is difficult to perform these in a reliable manner. Not only does one sometimes get an over- or undercorrection, but it is also possi- ble to induce irregular astigmatism. Patients sometimes experience for- eign body sensation or a worsening of dry eye from the incisions. Rarely, there are serious complications such as an infection or corneal perfora- tion. The femtosecond laser offers the opportunity to increase the precision of the incision depth, length, angular position, and optical zone, with better reproducibility than manual techniques, although admittedly at greater expense. The ability to perform intrastromal arcuate keratotomy (ISAK), rather than penetrating incisions, with the laser minimizes the risk of infection and patient discomfort. The limit- ed reports to date of intrastromal astigmatism correction suggest that it produces less effect than penetrat- ing correction, at least with current nomograms. Recently, we undertook a study to evaluate the safety and efficacy of ISAK and to gather data for improve- ment of our nomogram. Advanced technologies, including toric and multifocal IOLs and femtosecond lasers in cataract surgery, are an In the study, capsulotomy, lens fragmentation, and intrastromal astigmatic keratotomy were performed with the Catalys femtosecond laser. Source: David A. Salz, MD of 20% below the epithelium to 20% above the endothelium. The arc length was calculated using the Donnenfeld LRI nomogram. Assum- ing that non-penetrating incisions would have less effect, we compen- sated by moving the optical zone more centrally, to 8.0 mm. Interim results are available for 20 subjects with a mean age of 69.4 years (range 35–82), who have been followed out to at least 1 month, with about half reaching 6 months. Enrollment is continuing. Clinical results Even without knowing exactly how to adjust the penetrating LRI nomo- gram, the results with ISAK thus far have been excellent. Mean preoperative corneal astig- matism in the first 20 eyes was 1.43 D (range 0.25 to 3.00 D) by manual keratometry and 1.47 D (range 0.59 to 2.67 D) on the IOLMaster. One month postoperatively, us- ing manual keratometry, the residual refractive astigmatism was 0.74 D (range 0.25 D to 1.50 D), for a 0.67 D mean change in astigmatism. Using IOLMaster keratometry, the residual astigmatism was 0.71 D at 1 month and 0.60 D at 6 months. This was a statistically significant reduc- tion of preoperative astigmatism. There were no adverse events. The targeted surgically induced astigmatism (SIA) vector was 1.42 D. Vector analysis demonstrates that the actual SIA vector was 1.72 D, yielding a correction index (CI) of 1.16 overall. Ten of 20 eyes had a CI >1.0, 6 of 20 eyes had a CI of exactly 1.0, and 4 of 20 eyes had a CI <1.0. Qualitatively, ISAK is superior to the manual incisions we have made in the past. The intrastromal incisions are geometrically perfect and are created exactly as they are programmed. ISAK is less invasive than penetrating incisions, so we would expect it to be safer, minimiz- ing the risk of infection and increas- ing patient comfort. High quality, 3D imaging is critical to the safety of femtosecond laser ISAK because accurate identifi- cation of the epithelium and endo- thelium helps prevent an accidental penetration of either the anterior or posterior cornea. The surgeon should take care to observe there is no shift in the identified structures prior to treatment. It is not yet clear where the ideal optical zone is for ISAK. Other surgeons have taken a variety of approaches, adjusting their LRI nomograms by a certain percentage and/or moving the optical zone to between 9.0 mm and 7.0 mm. More work remains to develop ISAK-spe- cific nomograms, but once we can appropriately adjust existing nomo- grams for intrastromal incisions, we should be able to replicate or surpass the efficacy of manual LRIs with this technique, with enhanced safety and patient comfort. EW Reference 1. Ferrer-Blasco T, Montés-Micó R, Peixoto- de-Matos SC, et al. Prevalence of corneal astigmatism before cataract surgery. J Cata- ract Refract Surg. 2009;35(1):70–5. Editors' note: Dr. Salz is a fellow at the New England Eye Center at Tufts Medical Center, Boston. Dr. Salz has no financial interests related to this article. Contact information Salz: dasalz@gmail.com

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