Better refractive outcomes in cataract surgery

Take-Home

Throughout 2013, there were several studies done that showed various new technologies and advancements have not only shown better refractive outcomes in cataract surgery, but could continue benefiting the outcomes in the future.

By Cheryl Guttman Krader

In 2013, cataract surgeons gained access to new IOLs, a new phacoemulsification unit, and a new topical NSAID. However, according to Mark Packer, MD, perhaps the most important developments were in the areas of diagnostics, including technologies for intraoperative imaging and for bringing preoperative diagnostic information into the operating room.

“These innovations are changing the practice of cataract surgery,” said Dr. Packer, MD, private practice, Bowie, and clinical associate professor of ophthalmology, Oregon Health & Science University, Portland. “In the future, the location of care will be more operating room (OR)-centric and surgeons will be making more decisions in real-time during the operation.

“I think these developments, more than anything, are going to help us improve our surgical outcomes,” he said.

Citing the availability of intraoperative guidance systems for toric IOL implantation, Randall Olson, MD, agreed that these diagnostic tools are bringing cataract surgery into a new era.

“I expect we will be seeing more developments in this area in the future with the goal of increasing refractive precision,” said Dr. Olson, professor and chair, department of ophthalmology and visual sciences and chief executive officer, John A. Moran Eye Center, University of Utah, Salt Lake City.

Developments

Currently, there are three systems designed to register information from preoperative digital photography/topography to the eye intraoperatively as a way to guide accurate toric IOL alignment.

One of these platforms is the Verion Image Guided System from Alcon Laboratories, which was introduced after Alcon acquired the ophthalmic division of SMI.

Another is Callisto eye from Carl Zeiss Meditec, which uses the reference axis from the IOLMaster 500 and target axis in the microscope oculars as a guide for alignment.

Most recently, TrueVision 3D Surgical and i-Optics teamed up to create a system in which the topographic image obtained with the Cassini corneal diagnostic device (i-Optics) would be imported to the Refractive Cataract Toolset software (TrueVision) surgical guidance applications.

“The Cassini is an interesting new topographer that uses LED illumination and triangulates points on the cornea to give a much more accurate depiction of corneal elevation and with less possibility for missing small deviations that sometimes blend in when doing Placido disc topography,” Dr. Packer said. “Using any of these new systems, surgeons can achieve much better precision and accuracy in determining the correct axis for rotation of a toric lens in order to provide patients with better outcomes.”

Real-time refraction

Intraoperative aberrometry is another approach for improving refractive outcomes in cataract surgery whether using a toric or non-toric IOL.

As a key development during 2013, WaveTec Vision launched its new VerifEye monitoring system as a hardware upgrade for the ORA System.

VerifEye provides streaming refractions in a preview screen and thereby allows surgeons to confirm eye stability before taking a measurement. Dr. Packer described its introduction as the most important advance of the year in cataract surgery imaging.

“It is my experience that in the majority of cases where the lens power chosen by the intraoperative aberrometer is outside the range of powers calculated preoperatively, the aberrometer is correct,” Dr. Packer said. “However, sometimes the discrepancy has to do with exogenous factors affecting the accuracy of the intraoperative measurement, such as pressure from the lid speculum or lid squeezing by the patient.

“With VerifEye, surgeons can avoid these false measurements by watching for the streaming data on sphere, cylinder and axis to stabilize and then capturing data they can trust,” he said.

One limitation of intraoperative wavefront aberrometry, Dr. Packer said, is that it cannot account fully account for surgically induced astigmatism (SIA), which changes with incision healing.

Dr. Olson also cited this issue and the inability to account for final lens position, referencing a paper he published in 2012 [Stringham J, et al. J Cataract Refract Surg. 2012; 38 (3): 470-4]. Nevertheless, Dr. Olson said he believes intraoperative aberrometry allows for a more accurate measurement of the aphakic power state than what the surgeon can determine preoperatively, and he noted that some well-conducted studies provide evidence to show that refractive results are better using intraoperative aberrometry.

“The fact that we are seeing new competitor technologies coming along is clear evidence of enthusiasm and interest in this area,” Dr. Olson said.

Preoperative input

Aside from advances in intraoperative guidance tools, recent research points to areas in preoperative diagnostics with implications for achieving better results with toric IOL surgery.

Dr. Packer identified a recent paper by Doug Koch, MD, and colleagues the end of 2012 [Koch DD, et al. J Cataract Refract Surg. 2012; 38 (12): 2080-7] as a key event, as it showed conclusively that posterior corneal astigmatism contributes to total corneal astigmatism.

“This was groundbreaking work as it was the first to document the potential for under-correction in eyes with against-the-rule astigmatism and overcorrection in those having with-the-rule astigmatism when posterior corneal astigmatism is ignored,” Dr. Packer said.

Recognizing the importance of posterior corneal astigmatism-and the fact that all toric IOL calculators, whether developed by the IOL manufacturer or others, were based on anterior corneal keratometry measurements-Dr. Koch and colleagues went on to create a nomogram for adjusting toric IOL power that accounts for the effect of the posterior cornea without the need to actually measure it [Koch DD, et al. J Cataract Refract Surg. 2013 Oct 26 epub ahead of print].

“This nomogram is based on population means and the results for an individual patient may not be as accurate as they could be by obtaining the actual measurements,” Dr. Packer said. “However, it is an important step toward achieving improved results and the beginning of a new era of interest in diagnostic imaging technology that measures the posterior cornea.”

Currently there are three units with this capability:

·      The combined Placido-dual Scheimpflug analyzer (Galilei, Ziemer), used by the Baylor researchers

·      The dual rotating Scheimpflug camera (Pentacam, Oculus)

·      A spectral-domain OCT device (RtVue, OptoVue)

Dr. Packer noted that while the Scheimpflug-based devices determine the posterior surface curvature from pure imaging, the OCT device incorporates some mathematical fudge factors to correct for the magnification of the cornea.

“These three devices have assumed increased importance given the recognition now that surgeons can do a lot better in correcting astigmatism with toric IOLs if they use information about the posterior cornea as well, and we can expect their use to become more widespread,” Dr. Packer said.

Also important in the area of corneal diagnostics, Dr. Packer identified a paper by Denoyer et al. [Denoyer A, et al. J Cataract Refract Surg. 2013; 39 (8): 1204-10] that showed preoperative corneal biomechanical properties, as measured with the Ocular Response Analyzer (Reichert), had a statistically significant effect on surgically induced astigmatism (SIA).

The study reaffirmed a fact that is well known to cataract surgeons as well-that incision size influences SIA. However, corneal hysteresis (CH) had an even stronger effect.

The results showed that eyes with a higher preoperative CH value had less SIA than eyes with low preoperative CH.

Dr. Packer said the results make intuitive sense and suggest the possibility that taking corneal biomechanics into account can improve refractive outcomes.

“SIA continues to plague refractive cataract surgery, and it is the biggest source of error in toric IOL surgery excluding failure to account for posterior corneal astigmatism,” he said. “Even though surgeons can calculate their average SIA using data from a large population of eyes, there is still a large standard deviation of perhaps 0.5 D that doesn’t disappear no matter how many cases you do.

“So for a surgeon whose average SIA is 0.5 D, the actual SIA will be 0 in about 20% of eyes but 1.0 D in another 20%. The standard deviation hurts the results for the outliers,” he continued.

Dr. Packer proposed that in the future, surgeons could find themselves using different SIA values in their toric IOL calculations, depending on whether the patient has low or high preoperative CH. However, since the paper by Denoyer et al. is the first report of its kind, more research is needed to confirm the findings and to determine how to translate them into clinical practice.

Mark Packer, MD

E: mark@markpackerconsulting.com

Dr. Packer is a consultant to TrueVision Systems and WaveTec Vision.

Randall Olson, MD

E: randallj.olson@hsc.utah.edu

Dr. Olson has no relevant financial interests to disclose.