Eyeworld

EW FEATURE 64 '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 po- sition accurately." However, sur- geons can also use the Haigis-L formula if they have an IOLMaster (Carl Zeiss Meditec, Dublin, Calif.), 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 par- ticularly vulnerable to this phenom- enon, he said. Because of this, Dr. Hill recom- mended targeting a slightly more myopic refraction than actually de- sired, such as –0.50 D or –0.75 D. He outlines this in more detail at www.doctor-hill.com/iol-main/ postRK.htm. Dr. Hill said hyperopic drift in RK eyes makes it hard to estimate central corneal power. "This is due to the fact that the assumptions made by many devices do not line up with what's actually going on with the central cornea," he said. To help remedy this problem, Dr. Hill has had the most success with the ASCRS post-refractive calculator and the Zeiss Atlas topographer. Dr. Wiley's practice has recently started corneal crosslinking, which he believes helps to strengthen these corneas and decrease the diurnal fluctuations. "First you do the crosslinking to decrease the daily fluctuation, then you get a new pre- scription, and then you do cataract surgery. If you do cataract surgery first, you may have a perfect result, but crosslinking could shift the pre- scription in the wrong way," Dr. Wiley said. Handling refractive surprises Preparing patients for possible re- fractive surprises is key, Dr. Koch said. This often involves a careful conversation with patients before surgery, pointing out that their pre- vious refractive work makes their eyes more challenging. It also entails explaining to patients the extra costs that could be incurred from addi- tional LASIK or PRK procedures if necessary, Dr. Koch added. When a refractive surprise oc- curs, the choice that surgeons make may depend on cost issues—for ex- ample, whether or not they have their own laser center or ASC, Dr. Wiley said. "There are typically three op- tions: lens exchange, a piggyback lens, or LASIK or PRK. I typically go through those options with the pa- tient. If there is any astigmatism and if I've missed the target, I think the best option is a corneal refractive procedure like PRK," Dr. Wiley said. "With lens exchange, it's a little more challenging. It's easier to go back in, say we're going to do PRK, treat astigmatism, and feel confident we're doing it with one surgery." If a refractive surprise occurs in an RK patient, Dr. Hill recom- mended following the "rule of twos"—don't do anything until there are two stable refractions, two consecutive visits, 2 months after February 2011 Challenging cataract cases September 2011 Refractive continued from page 63 continued on page 68

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