EyeWorld Asia-Pacific December 2015 Issue

48 EWAP REFRACTIVE December 2015 Treating residual refractive error with PRK by Steven Schallhorn, MD Surface ablation post- multifocal IOL is effective, within reach for cataract surgeons P atients elect implantation of a multifocal IOL because they want to see well without glasses after cataract surgery. We know that a manifest refraction close to plano is directly associated with good uncorrected acuity. The greater the refractive error, the less likely a patient is to see 20/20 or better. Manifest refraction is also correlated with patient reports of being “very satisfied” with their multifocal IOL outcome. But all surgeons who implant multifocal IOLs will from time to time encounter patients who have a significant residual refractive error after surgery and are dissatisfied with the outcome. When this occurs, options for correction include IOL exchange or Step-by-step PRK for cataract surgeons Follow these steps for reliable, effective PRK enhancement after multifocal IOL surgery: • Insert lid speculum • Instill anesthetic drops • Place 9.0-mm circular well • Apply 18% EtOH in well for 30 seconds • Remove EtOH and irrigate • Gently remove epithelium • Ensure the bed is ready for treatment • Engage eye tracker and ensure centration • Perform excimer laser treatment • Instill medications • Apply bandage soft contact lens • Remove speculum repositioning, piggyback IOL, some form of astigmatic keratotomy (AK/ LRI), and laser vision correction. A recent retrospective analysis of data from Optical Express centers shows that both LASIK and PRK are safe and effective enhancement approaches. Given that PRK is easier to learn and may be more acceptable for cataract surgeons without significant corneal refractive surgery experience, I will focus on the results in eyes undergoing PRK post-multifocal IOL. Large enhancement sample We analyzed the results of PRK enhancement after multifocal IOL implantation in 724 eyes of 602 patients, with a mean age of 54 years (range 40–87 years). Slightly more than half the subjects (53%) were male. Most eyes (80%) were enhanced within 12 months of the initial multifocal IOL surgery. The sample includes patients who had PRK performed with the VISX S4 laser (Abbott Medical Optics, Abbott Park, Ill.). The average time from PRK enhancement to the last postop exam was 5.4 months. These patients had relatively low residual refractive error, with all eyes falling within the range of –3.00 to +2.50 D manifest spherical equivalent (MSE). An IOL exchange or piggyback IOL is preferred for larger corrections. Pre-enhancement, mean MSE was –0.40±1.05 D. The mean spherical error was +0.14±1.12 D and mean cylinder was 1.08±0.67 D. Post-enhancement, mean MSE was –0.14 ± 0.57 D. Nearly all eyes (98.9%) were within 1.0 D of intended refraction postop; 94.3% were within 0.5 D. Following PRK enhancement, mean sphere was reduced to +0.08±0.57 D and mean cylinder to 0.43±0.46 D. Uncorrected distance visual acuity improved significantly. Pre- enhancement, only 1.4% of eyes were 20/20 or better; that improved to 50.8% postop. Nearly all eyes were 20/40 or better postop. Why PRK? The reasons for the residual error after the IOL procedure in this retrospective study were not analyzed. But there are many possible reasons for not achieving the desired refractive outcome. In some cases patients had a low amount of corneal astigmatism and perhaps could have had an astigmatic keratotomy (or LRI) or even implantation of a toric IOL at the time of the IOL procedure. Astigmatism may have been induced at the time of surgery. A different lens power formula could have been chosen that would have led to a result closer to emmetropia. Or there was variability in the actual lens position. In any case, all of these patients had residual error and desired better visual acuity. Optical Express surgeons have ready access to excimer lasers, so the decision to proceed with laser vision correction was relatively easy in these cases with low residual error, provided there were no contraindications to corneal surgery. Next, surgeons would have been faced with the choice of PRK or LASIK. In my opinion, LASIK is an excellent choice, if it can be safely performed in the right patient. LASIK provides more rapid visual recovery, and in my experience it does not appear to induce more dry eye symptoms than PRK. However, not all surgeons will have access to appropriate flap-making technology for LASIK and not all multifocal IOL patients will be candidates for LASIK. PRK remains an excellent alternative. There are a number of potential techniques for removing the epithelium in a PRK or other surface ablation procedure, including alcohol-assisted epithelial removal (the technique used in the study described here), Amoils brush removal, mechanical debridement, transepithelial laser, and special keratomes to perform