EyeWorld Asia-Pacific September 2013 Issue

September 2013 25 EWAP FEAturE they may someday need a corneal transplant” and because it’s rare to have regular astigmatism in these eyes. In general, he advises adding “about a half diopter” of measured IOL power for a patient with four incisions, between 1-1.5 D for those with eight incisions, and 2 D for those with 12 or more incisions. While intraoperative aberrometry may be very useful in eyes having prior laser vision correction, it is less accurate in the post-RK eye, as corneal curvature changes during cataract surgery in these eyes, he added. The post-cataract refraction The key to judging the postop refraction in a post- cataract, post-RK eye “is to follow the keratometry values,” said Uday Devgan, MD , in private practice, Los Angeles, and chief of ophthalmology, Olive View – UCLA Medical Center. “The RK incisions tend to swell even during the gentlest of phaco surgeries and this causes transient central flattening of the cornea.” He advises measuring the preop Ks using an auto-keratometer and waiting until the eye returns to those K values before determining what the final refractive outcome of the cataract surgery is. No one can predict how long it will take the post-RK patient to return to pre-surgical curvature, Dr. Masket said, and the number of incisions, incision depth, central corneal zone size, and surgical details all factor into that timing. “They’re going to have an induced transient hyperopic error, and patients need to be very tolerant of this,” he said. Dr. Bowers tells patients it takes about two months for the refraction to stabilize, but “most patients will stabilize sooner than this.” Patients with four incisions tend to stabilize closer to four weeks, while those with eight or more take a full 2-3 months, she said. “If they experienced visual fluctuations preop, they’ll still experience them postop,” she said. If after three months there’s still a significant refractive surprise, options include PRK, LASIK, piggyback IOLs, or IOL exchange. EWAP Editors’ note: Dr. Bowers has no financial interests related to this article. Dr. Devgan has financial interests with Aaren Scientific (Ontario, Calif., USA), Alcon (Fort Worth, Texas, USA/Hünenberg, Switzerland), Bausch + Lomb (Rochester, NY, USA), Gerson Lehrman Group (New York, NY, USA), Accutome (Malvern, Pa., USA), and LensGen (Irvine, Calif., USA). Dr. Masket has financial interests with Alcon, Bausch + Lomb, Haag- Streit (Koniz, Switzerland), Ocular Therapeutics (Bedford, Mass., USA), PowerVision (Belmont, Calif., USA), and Carl Zeiss Meditec (Jena, Germany). Dr. Schechter has financial interests with Bausch + Lomb and Omeros (Seattle, Wash., USA). Contact information Bowers: 270-415-0245, barbbowersmd@comcast.net Devgan: 800-337-1969, devgan@gmail.com Masket: 310-229-1220, sammasket@aol.com Schechter: 561-737-5500, bdsch77@aol.com Views from Asia-Pacific FAM Han Bor, MD Senior Consultant & Head, Cataract & Implant Service The Eye Institute @ Tan Tock Seng Hospital 11 Jalan Tan Tock Seng, Singapore 308411 Tel. no. +65-6357-7726 Fax no. +65-6357-7718 famhb@singnet.com.sg R adial keratotomy is an incisional refractive surgery in which radial incisions are made on the cornea to flatten the central cornea, thereby reducing its power. Today, this procedure has been superseded by the more precise laser refractive surgery. Similar to post-laser refractive surgery, IOL power calculation after RK involves the determination of corneal power and correcting the effective lens position using the double-K adjustment in the modern IOL formulae. Determining the corneal power in post-RK is easier. Unlike in laser refractive surgery, the ratio of anterior corneal to posterior corneal curvature remains relatively unaltered. Thus, the error arising from using the conventional keratometry (e.g. automated or manual keratometry) is less as compared to that in post-laser refractive surgery. Nonetheless, conventional keratometry measures the transition zone between the central optical portion and mid-peripheral incisional portion of the RK cornea, leading to incorrect overestimation of the corneal power. There are ways to estimate the true corneal power, the simplest being to use the flattest K. If the clinical history is reliable, this method may be used to calculate the effective corneal power. For more accurate corneal power, the use of topography or tomography is recommended. The average corneal power within the optical zone or the central 3 mm has been shown to yield the best outcomes. I particularly like tomography as it gives the total cornea power, taking into consideration not just the anterior corneal power, but the posterior corneal power, as well as the corneal thickness. The double-K method should be used to adjust for the effective lens position. Unfortunately, post-RK corneas can fluctuate considerably with intraocular pressure, and with time. If the cornea curvature fluctuates significantly throughout the day, the postoperative outcomes would be less predictable. Transient hyperopic shift after cataract surgery is common post-RK. The shift can be as high as 3.00 D and may take a considerable time of 2 to 3 months to resolve. Intervention should be avoided until the postoperative refraction has stabilized. Patient reassurance is important during this recovery period. Due to corneal fluctuation and shift, I would generally avoid using multifocal lenses. If astigmatism is regular, I would put in a toric monofocal. If there is no significant astigmatism, I would implant a spherical aberration-compensating monofocal lens in this oblate eye. Editors’ note: Dr. Fam has no financial interests related to his comments.