EyeWorld Asia-Pacific September 2013 Issue

September 2013 20 EWAP FEAturE Cataract surgery in post-refractive surgery patients by Michelle Dalton EyeWorld Contributing Writer Performing complicated surgery doesn’t have to be excruciating—if you are meticulous in preoperative stages W ith the popularity of laser vision correction, it is extremely unlikely cataract surgeons will never encounter a patient who has undergone refractive surgery. But because the corneas of these patients have changed, planning for cataract surgery is a bit more complicated. “Most of our machines measure just outside this central area and then extrapolate values for the central cornea. This works well for virgin corneas, but not so well in eyes with prior LASIK, PRK, or RK,” said Uday Devgan, MD , in private practice, Los Angeles, Calif., USA, and chief of ophthalmology, Olive View – UCLA Medical Center. (See “Calculating IOL power in post-RK eyes” for more on that topic.) Plus, surgeons need to consider both the anterior and posterior corneal curvatures— the relationship between each An eye after previous RK and LASIK surgery Uday Devgan, MD Views from Asia-Pacific Cordelia CHAN, MD Head & Senior Consultant, Refractive Surgery Service Singapore National Eye Centre 11 Third Hospital Avenue, Singapore 168751 Tel. no. +65-6227-7255 cordelia_chan@snec.com.sg I n our cataract surgery practice today, we are encountering more patients with a prior history of laser vision correction or refractive surgery. Intraocular lens power calculations immediately become more complicated in these cases, as the patients’ corneas have been altered from the refractive treatment, and there is a higher chance of refractive surprise. Patient counseling, education and management of patient expectations are particularly important in these cases. Almost all patients would volunteer the history of previous refractive surgery, but there will be the occasional patient who would be unaware of its relevance and fail to disclose it. Most patients who have had LASIK can be easily identified during careful examination of the cornea with the slitlamp biomicroscope, but the occasionally barely perceptible microkeratome flap or pristine cornea following surface ablation procedures may avoid detection and slip through the cracks. Certainly, history taking is important in any case, but in the rare instance where prior cornea refractive surgery is overlooked, an astute biometry technician can alert the surgeon when unusually flat keratometry readings on routine biometry are encountered. When calculating intraocular lens power for these cases, we have to make do with whatever information case records show, or what the patient can provide, but often, no prior data is available. This makes choosing the correct IOL power a challenge. I tend to be obsessive and like running multiple formulas in calculating the IOL power in these cases. I find Hill’s ASCRS Post-Keratorefractive Intraocular Lens Power Calculator particularly useful. This is an online internet-based IOL power calculator that can be easily accessed through the ASCRS website. Various methods are used to calculate the IOL power here, including using pre-LASIK/PRK K values, surgically induced change in manifest refraction, and even no prior data. The average IOL power from these formulas is calculated and computed, and using this, I have had predictable results with about 90% accuracy in my cases so far. Counseling these patients and down-playing their expectations of spectacle independence is extremely important. I usually educate the patient on the difficulties of IOL power calculations and the possible need for IOL exchange or laser enhancement surgery to correct any refractive surprise. These refractive surgery patients are likely to demand spectacle independence for both distance and near more so than other patients, and the topic of multifocal lens implantation is often unavoidable. I generally prefer not to implant multifocal IOLs in these patients, as the visual results can be unpredictable. In particular, I avoid multifocal IOLs in patients with increased higher-order aberrations and decentered ablations following refractive surgery. When choosing the intraocular lens power, it is better to aim for slight myopia. In the event of a refractive surprise, myopic corrections tend to be more predictably corrected with laser enhancement surgery, which is my preferred method over IOL exchange. For surgeons without access to an excimer laser system, IOL exchange will then have to be performed, and this should be done sooner rather than later following the initial cataract surgery. Editors’ note: Dr. Chan has no financial interests related to her comments.