EyeWorld India June 2017 Issue

June 2017 EWAP CORNEA 47 by Rich Daly EyeWorld Contributing Writer Preop corneal irregularity approaches for cataract patients Surgeons discuss the use of topographic or wavefront ablations, Intacs, and CXL to treat corneal irregular astigmatism or stable keratoconus patients before cataract surgery. P atients with corneal irregular astigmatism or stable keratoconus can add a layer of complexity to the typical treatment of cataract patients. But surgeons have identified effective approaches for them. In patients wearing rigid gas permeable (RGP) lenses or who have a longstanding history of reduced best spectacle-corrected visual acuity (BSCVA) secondary to irregular astigmatism, Raymond Stein, MD , FRCSC , medical director, Bochner Eye Institute, and associate professor of ophthalmology, University of Toronto, prefers to perform topography-guided PRK and corneal collagen crosslinking (CXL) prior to cataract surgery. “The goal is to reduce irregular astigmatism so that patients following cataract surgery will be free of RGP lenses and be able to wear glasses, soft contact lenses, or be free of optical aids,” Dr. Stein said. Patients need to discontinue wearing RGP lenses for at least 1 month or until topographic stability is reached. On average, stability is reached around 6 weeks but may take up to 4 months. Simon Holland, MB , FRCSC , Pacific Laser Eye Centre, Vancouver, approaches such patients like post-refractive surgery patients. They require additional consent to have realistic expectations amid the increased unpredictability. He determines the degree of keratoconus—less than 49 K is mild, 50–55 is moderate, and greater than 55 is severe—and identifies the location of the cone. That is followed by multiple programs and imaging, including equivalent K readings with the Pentacam (Oculus, Wetzlar, Germany) and posterior curve with the Sirius Corneal Topographer (CSO, Scandicci, Italy). Good results are also provided by topography-derived or manual K at the 3-mm axial zone with the SRK-T or SRK-II formulas. “If using actual Ks, he suggests aiming for –1.50 with low KC, –2.0 up to 55, and use 44.0 as the target for over 55 with a view to doing topography-guided PRK with CXL later,” Dr. Holland said. Dr. Holland advises all such patients that they may need to resume RGP lenses or undergo topography-guided PRK with CXL. Surgical approach On the day of surgery, Dr. Stein obtains eight topographic images and transfers that information to the excimer laser for the treatment. The treatment plan is reviewed with the goal of limiting the excimer stromal ablation to 50 microns. “My preference is to use the larger optical zone of 6.5 mm or 6.0 mm, which reduces regression of the laser treatment,” Dr. Stein said. A phototherapeutic keratectomy is applied at 50 AT A GLANCE • Consider topography-guided PRK and CXL prior to or after cataract surgery in RGP wearers with irregular corneal astigmatism. • Consider topography-guided PRK instead of Intacs in corneas that are 450 microns or thicker. • Intacs reduce the irregular astigmatism in corneas that are less than 450 microns centrally. 72-year-old male with marked irregular astigmatism who received topography-guided PRK and CXL. Cataract surgery with a toric implant was performed 6 months after the corneal procedures. Patient did well and functions with glasses for reading only. Source: Raymond Stein, MD, FRCSC continued on page 48