EyeWorld Asia-Pacific March 2019 Issue

EWAP FEATURE 13 Views on astigmatic keratotomy by Rich Daly EyeWorld Contributing Writer AT A GLANCE • Astigmatic keratotomy treats the astigmatism on the cornea itself by flattening the steep meridian. • About 0.5–1.0 D is the ideal treatment range for AKs. • Femtosecond AKs are done with OCT guidance for more precision both in the depth of the incision and the centration on the visual axis. • Avoid using AKs in corneas that are thin or irregular or those with asymmetric astigmatism. The use of astigmatic keratotomy continues to change amid newer options A stigmatic keratotomy (AK), one of the two primary ways of surgically treating astigmatism, has changed in recent years with newer technology and understandings of its anatomical impacts. Treating corneal astigmatism at the time of cataract surgery remains critical to improve visual outcomes and decrease reliance on glasses. Although the newer option of toric IOLs to offset corneal astigmatism by neutralizing the astigmatic effect is popular with some patients, treating it at the source by decreasing the corneal astigmatism remains an important option. Generally performed with diamond knife incisions in the cornea, AK treats the astigmatism on the cornea itself by flattening the steep meridian so that the cornea becomes more spherical. “The corneal power in that meridian is slightly weakened by creating partial depth incisions either with a blade or a laser,” said Uday Devgan, MD, clinical professor of ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles. The classic AK is placed from the surface of the cornea to 80–90% depth, noted Eric Donnenfeld, MD, clinical professor of ophthalmology, New York University, New York. Dr. Donnenfeld said intrastromal incisions may be placed in the stroma and not penetrate through to the epithelium with a femtosecond laser and penetrating incisions can be made with a keratome. Incisions placed in the peripheral cornea—astigmatic keratotomies—are different than corneal incisions placed closer to the limbus, which are often referred to as limbal relaxing incisions (LRIs). Surgeons should consider using AKs in eyes with corneas that have a modest amount of astigmatism but are otherwise normal, Dr. Devgan said. They are usually done at the time of cataract surgery and tend to work well to treat 0.5–1.0 D of corneal astigmatism. Dr. Donnenfeld noted that AKs also can be performed as standalone procedures. The incisions can be used for higher degrees—up to 2.0 D—but they tend not to be as accurate at that level of astigmatism, Dr. Devgan said. “I favor LRIs for 0.5–1.0 D of astigmatism and toric IOLs for 1.5 D or more of astigmatism,” Dr. Devgan said. Femto option Femtosecond laser astigmatic incisions used to reduce astigmatism provide more precision than a manual diamond knife incision, Dr. Donnenfeld said. “They are done with OCT guidance so the depth of the incision is more precise as well as their centration on the visual axis,” Dr. Donnenfeld said. “Femtosecond laser astigmatic incisions can be titrated by manually opening them during the postop period based on the refraction.” Dr. Devgan agreed that femtosecond AKs have the benefit of laser precision so that the depth of the AK can be made exactly at 80% or another level for the entire length of the incision. “Since the femto incision does not automatically open like a diamond blade incision would, we can use that to titrate the AK effect by opening it in stages,” Dr. Devgan said. “So the femto AKs A patient undergoes manual AK. Slit lamp exam of a patient who received an AK treatment. Continued on page 14 March 2019