Intraoperative aberrometry slashes cataract enhancement rate

One surgeon sees a sixfold reduction in re-treatments.

A major goal of modern cataract and refractive lens surgery is an astigmatically neutral postoperative result. Physicians use tools such as limbal relaxing incisions or the implantation of IOLs to help patients achieve the best possible results. Wavefront aberrometry has helped surgeons immensely in their preoperative planning, but until now, surgeons have not had the possibility of checking refractive error and confirming incision locations perioperatively.

ORange (WaveTec Vision) is an intraoperative aberrometer based on Talbot Moiré interferometry that provides wavefront-guided refraction on patients during cataract (or lens exchange) surgery. The device analyzes sphere, cylinder and axis, and essentially enables the surgeon to make decisions regarding the need to reduce residual and/or induced astigmatism while performing the procedure. For many years, I created limbal relaxing incisions based on preoperative measurements, but I have discovered that I am getting better outcomes by using the device to verify astigmatism correction during surgery.

More than 1,800 eyes have been treated using this intraoperative wavefront system. After a year of using the intraoperative aberrometer as part of the company’s beta testing, I discovered its positive impact on my re-treatment rate. Prior to implementing ORange into my surgical armamentarium, my enhancement rate was about 18%; that rate has since been reduced to nearly 3%. This represents about a sixfold reduction in re-treatments.

After several months of using the aberrometer for other study purposes, I implemented the option of extending limbal relaxing incisions or performing intraoperative enhancements while the patient was still in surgery. My enhancement criteria were: If the measurement was within 15° of expected and more than 1 D of cylinder, then I would extend the limbal relaxing incision. If it was below 1 D and I thought the patient would be fine ending up with 0.5 D or 0.75 D of cylinder postoperatively, I did not extend the limbal relaxing incisions.

Mark Packer, MD, and colleague work with intraoperative wavefront aberrometry during cataract surgery. Image: Packer M

In order to better evaluate the impact of ORange on my patients’ results, I completed a retrospective study of re-treatments with respect to patients with whom I used the aberrometer perioperatively and those with whom I used preoperative measurements. Preoperative topography, keratometry and corneal pachymetry readings were analyzed, as well as postoperative refractions and information about whether the patients needed — or wanted — an enhancement.

The study evaluated 67 eyes of 48 patients between May 2007 and June 2009 who opted to have correction of pre-existing corneal astigmatism by limbal relaxing incisions at the time of cataract surgery or refractive lens exchange. The patients were divided into two groups. The control group comprised patients who had limbal relaxing incisions but no wavefront measurements, or patients from the first year of the retrospective study group, and the aberrometry group consisted of patients treated with limbal relaxing incisions who had intraoperative wavefront measurements and therefore may or may not have had an intraoperative limbal relaxing incision extension based on the wavefront measurements.

The retrospective analysis demonstrated that using an intraoperative aberrometer had a positive effect on my postoperative enhancement rate during the time analyzed. In the first year without using ORange measurements to do intraoperative enhancements, six postoperative re-treatments were necessary for the cohort of 37 eyes. In the second year of the study, when I was using ORange measurements intraoperatively, I had only one postoperative re-treatment out of a group of 30 eyes.

The retrospective study clearly showed a positive impact of wavefront-guided limbal relaxing incisions at the time of surgery on the rate of future postoperative laser enhancement. In the first group of 37 eyes of patients who were not measured with the device, six out of 37 eyes, or 16%, went on to have LASIK enhancement. In the second group of 30 eyes of patients who were measured with the device, only one of the eyes, or 3%, went on to have LASIK enhancement — because eight out of the 30, or 27%, had received intraoperative limbal relaxing incisions during the primary procedure based on aberrometer findings. The groups had similar pre- and postoperative characteristics.

Due to the small size of the study and the inequality between the study groups, the reduction in enhancements does not show statistical significance. However, the trend that was demonstrated makes an appealing case for further studies that can validate the importance of interoperative aberrometry.

ORange-assisted technique

Here is how ORange fits into my operative routine. Once the IOL is well-positioned and the lens has been allowed to unroll, I introduce a little more viscoelastic, because a solid pressure of at least 25 mm Hg is necessary to get an accurate measurement with the device.

At that point, we turn off the microscope light and set the aberrometer to take measurements. I do an initial measurement of the astigmatism, and in most cases it correlates very closely to my preoperative corneal topography measurements. However, it varies in just enough instances to make it an invaluable addition to my surgical plan. If the reading is higher or lower than what I have discerned preoperatively, I adjust the length of the arcs. Sometimes, based on the readings produced, I decide not to cut arcs at all. I had a recent case where I was planning to do limbal relaxing incisions, but when I got my ORange reading, it showed that there was less than 1 D of cylinder, so I changed my surgical plan. Results I have seen from my own study and others to date show that if there is less than 1 D at the time of surgery, the patient does not need limbal relaxing incisions, as the final diopter generally ends up being about 0.5 D or less postoperatively.

Once I make my initial cut, I take another measurement with ORange to see what the impact has been and decide if the arcs need to be extended. After that, I take a final measurement and then perform irrigation and aspiration and seal my incisions.

ORange and outliers

One of the ways that this device proves its value is in preventing outliers, which can be a substantial expense for a practice. There is a tremendous savings associated with preventing re-treatment with a LASIK enhancement. Enhancements cost the practice not only the extra time involved in patient education and additional treatment, but also the cost of the dissatisfied patient, including the possible loss of reputation. The use of intraoperative aberrometry appears to almost eliminate outliers.

An excellent example of the device’s usefulness lies in a recent case. I had a patient who previously had LASIK whose initial preoperative corneal topography astigmatism reading was about 1.25 D at about 100°. But when we did the ORange measurement, it turned out to be closer to about 114°. I was able to rotate my arcs to take that into account. One day postoperatively, the patient was 20/20^–1. While it takes a month for everything to settle down and to get to a point of stability, so far it looks like the rotation based on the ORange measurements was the right choice. An enhancement was avoided in this particular case.

Again, the cost of an enhancement goes beyond the surgery center fee and other associated monetary outlays. It is the cost of the patient who returns after surgery and says, “I can’t see well,” and then tells friends and associates, “I had surgery with Dr. Packer and look what happened.” You literally cannot put a price tag on the ability to have a completely successful surgery the first time around.

Reference:

• Packer M. Effect of intraoperative aberrometry on the rate of postoperative enhancement: Retrospective study. J Cataract Refract Surg. 2010;36(5):747-755.

• Mark Packer, MD, is a clinical associate professor of ophthalmology at the Oregon Health & Sciences University. He can be reached at Drs. Fine, Hoffman & Packer, LLC, 1550 Oak St., Suite 5, Eugene, OR 97401; 541-678-2110; fax: 541-484-3883; e-mail: mpacker@finemd.com.