September 2015




Treating residual refractive error with PRK

by Steven Schallhorn, MD


Surface ablation post-multifocal IOL is effective, within reach for cataract surgeons

Patients 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 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 4087 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 0.401.05 D. The mean spherical error was +0.141.12 D and mean cylinder was 1.080.67 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 +0.080.57 D and mean cylinder to 0.430.46 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 epi-LASIK. Of these, alcohol removal is highly reliable without requiring specialized instruments or equipment.

In summary, in this large sample of 602 patients who underwent PRK following multifocal IOL implantation, a significant reduction in sphere and cylinder was achieved with good refractive predictability. Uncorrected distance vision improved with no mean change in best corrected acuity. PRK is an effective procedure for the correction of low refractive errors after multifocal IOL surgery and one that is easy for cataract surgeons to learn.

Editors note: Dr. Schallhorn is global medical director of Optical Express and professor of ophthalmology at the University of California San Francisco. He has financial interests with Abbott Medical Optics and Carl Zeiss Meditec (Jena, Germany).

Contact information


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

Treating residual refractive error with PRK Treating residual refractive error with PRK
Ophthalmology News - EyeWorld Magazine
283 110
283 110
True, 9