EyeWorld Asia-Pacific December 2011 Issue

27 EW CATARACT/IOL December 2011 surprise. That’s not a large volume of patients, but it does crop up,” Dr. Blecher said. IOL calculations Another major challenge in treating patients who have had previous refractive surgery is using an appropriate IOL calculation. Although there are numerous formulas available to calculate appropriate IOL power, one tool surgeons said they commonly use is the ASCRS post-refractive surgery IOL calculator (http://iol.ascrs. org/). “We enter all data available into the calculator,” said Dr. Wang, who is involved in the design of the calculator. “In the output section, we pay more attention to results derived from formulas relying on part of the historical data [change in manifest refraction induced by LASIK/PRK] and current measurements [methods in the middle column] and methods requiring no prior data at all [methods in the right-hand column].” “I think in general the ASCRS calculator is good—it gives a median option and a higher and lower one,” Dr. Wiley said. “I use it with all my patients if I have the previous refractive history.” When Dr. Wiley does not have previous refractive information, he uses the WaveTec (Aliso Viejo, Calif., USA) ORange aberrometer to fine-tune the best IOL choice. The ORange lets surgeons take intra-operative refractive measurements. Dr. Huang commonly uses the IOL calculation formulas available on the website of Warren Hill, MD, Mesa, Ariz., USA (www.doctor-hill.com). When working with IOL calculation formulas in these patients, the double K version must be used, Dr. Wang said. “The best way to do this is to use the Holladay Consultant Program [Bellaire, Texas, USA],” Dr. Wang said. “One should select the button ‘Previous LASIK/PRK/RK …’ In this way, pre-LASIK/PRK K value or an average corneal power of 43.86 D is used to predict the effective lens position accurately.” However, surgeons can also use the Haigis-L formula if they have an IOLMaster (Carl Zeiss Meditec, Dublin, Calif., USA), said Dr. Wang, praising the Haigis-L as one of the best formulas available. RK patients: A bigger challenge Surgeons agree that patients with previous RK require an even stronger strategic approach. “We measure RK patients with just about every device we have and some we find on the street,” Dr. Koch joked. “Due to the RK incisions, the cornea is more irregular, and it’s more difficult to obtain an accurate corneal power reading,” Dr. Wang said. Post-RK corneas are not stable and tend to continuously flatten, she added. “Over 8 to 16 weeks, this effect gradually diminishes, but I have seen some patients start out at +5 the day after surgery only to end up myopic 4 months later,” Dr. Hill said. Patients with more than eight incisions, small optical zones, and very deep or long incisions are particularly vulnerable to this phenomenon, he said. Because of this, Dr. Hill recommended targeting a slightly more myopic refraction than actually desired, such as –0.50 D or continued on page 31