Technology: investigational aberrometer offers real-time intraoperative refraction

October 1, 2008

An aberrometer is being developed to provide cataract and refractive surgeons with a tool for intraoperative assessment of refraction to improve results of astigmatic correction techniques and IOL power selection. Outcomes in an ongoing clinical trial are encouraging.

Key Points

Largo, FL-Clinical-trial experience with an investigational intraoperative aberrometer (WaveTec Vision) indicates that real-time analysis of changes to the refractive status of the eye is possible.

Although further refinements to this technology are needed, it is showing great promise for providing cataract and refractive surgeons with a diagnostic tool for guiding their surgery and improving results of astigmatic correction with limbal relaxing incisions (LRIs) and toric IOLs, said Robert J. Weinstock, MD, a cataract and refractive surgeon in private practice at the Eye Institute of West Florida, Largo, FL.

"It's estimated that up to half of patients with cataract have at least 0.5 D of corneal astigmatism, but that less than 10% of them undergo astigmatic correction at the time of surgery," Dr. Weinstock said. "Considering the large and growing demand for presbyopia-correcting IOLs along with the high expectations of baby boomer and post-refractive surgery patients undergoing cataract surgery, surgeons are charged with addressing astigmatism to provide better postoperative results.

The intraoperative device uses Talbot Moiré interferometry. It has a high dynamic range (–15 to +25 D) and, therefore, can be used to evaluate the spectrum of eyes ranging from high myopia to aphakia. It measures sphere and cylinder with a resolution <0.1 D as well as cylinder axis and higher-order aberrations.

The device mounts on the bottom of the operating microscope, and although in its current iteration the aberrometer does not interfere with intraoperative visualization, a more compact system will be forthcoming. The aberrometer data appear on a freestanding monitor. Surgeons also can obtain a printout of the displayed information and have it transmitted to a server for later analysis.

The intraoperative aberrometer is being evaluated in a multicenter, prospective clinical trial with eight participating investigational sites nationwide. Dr. Weinstock is among the investigators in this study, which is enrolling 150 cataract surgery patients who are scheduled to undergo either LRIs or toric IOL implantation. The study is evaluating the accuracy of the device for guiding surgical correction of astigmatism by comparing the pseudophakic refractive cylinder measured intraoperatively with the 3-month manifest refraction.

"The results are positive so far, with a good match between the intraoperative and postoperative measurements in a large percentage of patients. However, fine-tuning is needed to improve the predictability so that we can trust the intraoperative data to guide intraoperative manipulations of incision length and IOL position," Dr. Weinstock said.

Ongoing development likely will require further understanding of the influence of surgical variables and progression of the healing process as well as additional study of the difference in objective and subjective refractions. To this end, every eye with a difference of >0.75 D comparing the intraoperative and postoperative refractive measurements is being analyzed to identify factors that may contribute to the change.

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