Eyeworld

EW CORNEA 116 February 2018 by Stefanie Petrou Binder, MD, EyeWorld Contributing Writer Surgically induced astigmatism Central to the efficacy of incision- al surgery is avoiding surgically induced astigmatism (SIA), which is strongly coupled with incorrect axis. According to Thomas Kohnen, MD, Department of Ophthalmol- ogy, Goethe University, Frankfurt, Germany, manually placed AKs and LRIs have some limitations com- pared to femtosecond laser-made corneal incisions, which are more precise. Manual incisions in cataract surgery are commonly performed in high myopes using diamond knives and can be associated with irregular- ities of size and shape, which can be the cause of SIA. In a study that fo- cused on the effect of incorrect axis on astigmatism induction, placing corneal incisions that were off axis by 10 degrees lowered the efficacy of surgery by 34%, and those that were off axis by more than 30 degrees in- duced astigmatism. Overcorrections or the incorrect placement of the surgical components both can lead to incorrect axis and potential SIA, and need to be carefully avoided. "Corneal incisions can either be performed manually or using the femtosecond laser, which is much more accurate and may allow standardization," Dr. Kohnen said in a presentation on the topic at the XXXV Congress of the ESCRS. "Femtosecond laser corneal inci- sions may be the future for doing our incisional surgery." thing of an evolutionary variant of AK, which involves corneal incisions that are placed closer to the limbus. Both techniques represent effective refractive surgical procedures that can either be performed manually or by femtosecond laser, and continue to be valuable tools for astigmatism reduction despite the extensive use of LASIK. eye's steepest meridian, as a means of remediating mild to moderate levels of astigmatism. This allows the cornea to relax and take on a more rounded shape. Two effective methods to achieve this end include astigmatic keratotomy (AK), which implements corneal cuts, and limbal relaxing incisions/peripheral corneal relaxing incisions (LRI/PCRI), some- The femtosecond laser may be the future of corneal incisional surgery I ncisional surgery within the framework of irregular corneal management is associated with placing one or two corneal incisions perpendicular to the Astigmatism management: Corneal incisions Presentation spotlight The capsulotomy, lens fragmentation, and intrastromal AK performed using a femto laser. Source: David Salz, MD of the cornea," Dr. Cheung said. "We'll also keep them on long-term topical broad-spectrum antibiotics and sometimes topical antifungals as well. Daily topical antimicrobi- als along with a topical 5% povi- done-iodine wash at regular visits can decrease the bacterial loads and fungal colonization on the ocular surface." Dr. Aldave noted that cor- neal stromal necrosis occurs in approximately 25% of patients. It's more common in patients who have certain conditions, like Stevens-Johnson syndrome or previous chemical injury, and can result in the need to repair the area of corneal necrosis and/or replace the keratoprosthesis. "Addition- ally, elevated intraocular pressure develops in about 25% of patients following KPro surgery. However, it is important to note that 80% of my patients already have glaucoma before they get a keratoprosthesis. So, saying that patients with KPros commonly develop glaucoma is not accurate because most of them already have glaucoma prior to surgery. Many of these patients do develop progression of glaucoma following surgery, but that's the natural history of glaucoma any- way. I think the best way of putting it is that there's a risk of glaucoma development in the 20% of patients who don't have glaucoma prior to surgery or a risk of acceleration of the rate of glaucoma progression in those who already have glaucoma prior to KPro surgery. In an effort to prevent that, we put tube shunts in a large percentage of patients at the time of KPro surgery. We are aggressive with managing glaucoma with medications and monitoring it using multiple means, including au- tomated perimetry, nerve fiber layer thickness measurements, and scleral pneumotonometry after surgery," Dr. Aldave said. EW Reference 1. Aravena C, et al. Long-term visual outcomes, complications, and retention of the Boston type I keratoprosthesis. Cornea. 2018;37:3–10. Editors' note: Drs. Aldave and Cheung have no financial interests related to their comments. Contact information Aldave: aldave@jsei.ucla.edu Cheung: aycheung8@gmail.com What's continued from page 114 continued on page 118

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