Eyeworld

EW FEATURE 43 Surgeons have a multitude of biometric tools to use, but there is still some need for fine-tuning A s corneal refractive sur- geons implant more and more advanced technol- ogy IOLs for the treat- ment of both presbyopia and astigmatism, pre-op biometry will become increasingly important, especially when patients are footing the bill, surgeons said. "For virgin eyes that have not had any previous corneal surgery, the technology has gotten amaz- ingly accurate for K readings and axial length," said Vance Thompson, M.D., director, refrac- tive surgery, Sanford Clinic, Sioux Falls, S.D. "But we could still use im- provement with effective lens posi- tion." Calling pre-op biometry "the most critical part of the patient's cataract surgical process," Peter A. Rapoza, M.D., Ophthalmic Consult- ants of Boston, said that surgeons may have perfected the technique of cataract removal and IOL implanta- tion, but if the biometry is wrong and the patient's optical goals are not achieved, the patient will not be happy. "I think as surgeons we don't al- ways appreciate the vagaries of bio- metry where mistakes can be made, even in the virgin eye, nevermind one that's undergone RK, PRK, or LASIK," he said. He added that in- consistency in surgical rhexis tech- nique may adversely affect lens position, and personalized surgeon A constants "also make a differ- ence." There's still room for improve- ment in biometry, said Richard L. Lindstrom, M.D., adjunct professor February 2011 August 2011 Ethics of IOLs by Michelle Dalton EyeWorld Contributing Editor Pre-op biometry: Still not there yet International point of view Beirut, Lebanon T here is no doubt that the practice of ophthalmology in the Middle East parallels that in North Amer- ica and Europe with regard to pre- op biometry and keratometry. As long as we have new corneal and lenticular refractive techniques, we con- tinue to face challenges in accurate ker- atometry (K) measurements and effective lens position when it comes to cataract sur- gery. The most challenging cases we face are eyes that have undergone previous keratorefractive procedures, such as radial keratotomy, photorefractive keratectomy, and LASIK. For example, the patients who were among the first to pay out of pocket to undergo radial keratotomy 20 years ago have high expec- tations of their cataract surgery. They are still willing to pay for al- ternative lens implants like toric or multifocal lenses but want a guarantee of post-op near emmetropic uncorrected vision. This re- sult can be challenging to achieve in spite of thorough pre-op test- ing, including the use of the latest advanced technologies. There is an increased awareness among surgeons to follow certain formulas for certain eyes, but these do not eliminate the refractive surprises despite the continued fine-tuning of IOL formulas. The multitude of such formulas shows that not one of them is all-inclusive. As we introduce new corneal shapes, including monofocal and multifocal ablations with induced changes in spherical aberration, we will need to research the best lens implants for the best outcome when the crystalline lens comes out in every such case. To start with, it might be a good idea to provide patients a card with their "fingerprint" keratometry and axial length at some point when their eye exam and measurements are stable. This is helpful for patients who eventually develop very dense cataracts or poste- rior subcapsular cataracts, in which axial length measurements may be difficult to perform using technologies other than immersion A- scan. Furthermore, it is a good practice to provide patients who un- dergo corneal excimer laser ablations a piece of paper documenting their pre-op Ks and manifest refraction as well as the details of their laser ablation, together with a manifest refraction between 6 months and 1 year. This is already done in some centers. Often, we do not have access to such information, especially in patients who relocate frequently to other cities and countries. In the ideal world, we would have a one-stop examination that took into consideration previous history and types of refractive sur- gery, keratometry, topography, axial length, anterior chamber depth, and spherical aberration, and then determined the most rec- ommended and least recommended intraocular lenses. Not only should such a test be accurate, but it should also be relatively inex- pensive, accessible, and not time-consuming. As long as we introduce new refractive techniques, our current pre-op tools for IOL selection will have to be revised. Contact information Jabbur: nsjabbur@yahoo.com emeritus, ophthalmology depart- ment, University of Minnesota, Min- neapolis, and founder, Minnesota Eye Consultants, Minneapolis. "What we'd like to have, but don't quite yet, is a single instrument that would give us both keratometry and biometry and that would measure the cornea's higher-order aberra- tions," he said. A cataract's density "brings an error into the measurement of the axial length that perhaps we could learn to adjust for, but we haven't yet," Dr. Lindstrom said. "We still don't do very well when it comes to measurements in the distorted eye either." As a result, his group meas- ures eight different things in an aberrated eye. "There's a lot of room for improvement there." In non-virgin eyes that have un- dergone previous corneal surgery or trauma, K measurement accuracy is diminished, Dr. Thompson said. He thinks technology can be improved in the ability "to measure corneal power accurately and to do it objec- tively with no extrapolation." The "multitude of formulas" surgeons have available to them means "there's still room for im- provement on these," Dr. Thompson said, adding he "looks to people like Jack Holladay [M.D.] and Warren Hill [M.D.] when it comes to formu- lations. No, we haven't gotten to a point where we can rest on current technology." The Holladay II uses "unknown parameters to improve outcomes in short eyes in particular," Dr. Lindstrom said, adding the "most errors occur" in eyes outside the 22- 25 axial length range. Easy to overlook Dr. Rapoza said his group's desig- nated diagnostic technicians spend their entire workday on diagnostic workups, from immersion A-scans to IOLMaster (Carl Zeiss Meditec, Dublin, Calif.) calculations. "Our group always performs both tests for assessing axial lengths on both eyes, even if we're only planning surgery on one," he said. Both Drs. Rapoza and Lindstrom also emphasized the importance of calibration to guarantee the most accurate readings. AT A GLANCE • Biometry readings are much more reliable in virgin eyes than in non-virgin eyes • Intraoperative aberrometry may be the next big thing • Using a multitude of biometric readings and taking the mean will provide the best potential outcomes continued on page 44 Improving the accuracy of pre-op bio- metry and keratometric measurement Nada Jabbur, M.D.

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