Toric lenses failing to reach full market potential
Nailing toric IOL alignment with new technologies
Toric intraocular lenses (IOLs) provide a safe and predictable method of correcting pre-existing corneal astigmatism in cataract patients, so why are they implanted in only a small percentage of the eyes that would benefit most from their astigmatism-correcting properties?
Several factors are responsible for the failure of toric IOLs to reach their full market potential. Price certainly plays a major part, as the lenses are more expensive than traditional spherical monofocal IOLs and are only partly reimbursed, if at all, by national health systems. But that’s not the whole story, as Rudy MMA Nuijts MD, PhD, Professor of Ophthalmology at the University Eye Clinic Maastricht UMC+, The Netherlands, told EuroTimes.
“We are a little bit disappointed and concerned by the low uptake of toric lenses. Even at a conservative estimate, at least 20% of cataract patients are eligible for toric lenses. About half of these patients do not want to pay extra for a toric lens, but that still leaves 10% that are eligible. Yet the toric implantation rate in The Netherlands is only 3.5% to 4%,” he said.
The real reason for such slow uptake, believes Dr Nuijts, stems from the reluctance of many surgeons to offer toric IOLs to their patients.
“A recent survey of IOL implantation rates in European countries reported only one in three ophthalmologists expressing an interest in using toric IOLs. Many surgeons simply don’t want the hassle of dealing with extra measurements, marking of the eye, alignment and so forth. There is also the idea that if the lens can rotate in the eye then it is perhaps better not to take the risk at all,” he said.
The only way to counteract such hesitancy is through better advocacy and education, said Dr Nuijts. “It is evident from randomised controlled trials that lenticular solutions are much better than incisional solutions, and even femtosecond laser incisions are not going to be comparable with toric IOLs. We need to work harder to convince our colleagues of the benefits of these lenses,” he said.
HIGH-TECH INTRAOPERATIVE TOOLS
Advocates of toric IOLs can point to a long and growing body of controlled studies in the scientific literature attesting to the improved accuracy, visual outcomes and rotational stability of the latest-generation toric IOLs.
Improvements have been made in all areas: lens designs and materials have helped, as have more precise and comprehensive preoperative measurements which take account of factors such as posterior corneal curvature and surgically-induced astigmatism.
But perhaps the greatest evolutionary step has been the proliferation of intraoperative technologies designed to remove some of the remaining sources of error in toric IOL procedures such as corneal marking, axis alignment and centration of the lens.
“I think we are much more confident now putting in toric IOLs with lower cylindrical correction, which has a lot to do with the predictability of the measurements and the more accurate placement of the lens during surgery,” said Erik Mertens MD, FEBOphth, an ophthalmologist in private practice in Antwerp, Belgium.
In Dr Mertens’ practice, toric lenses represent about 22% of the lenses implanted, a reflection of the confidence he has in the array of technology he uses to fine-tune his toric IOL outcomes.
For preoperative measurements of the anterior and posterior cornea, Dr Mertens uses the Sirius System (CSO), combining a Scheimpflug camera and Placido disk. As well as topography and corneal aberrometry, the Sirius provides keratometry (K)-readings and tools to assist with the optical placement of the IOL to correct astigmatism. Further K-readings are obtained using the manual Javal-Schiotz keratometer and swept-source optical coherence tomography (SS-OCT, IOLMaster 700, ZEISS), which also provides advanced biometry of the eye.
To complete the preoperative analysis, Dr Mertens performs spectral-domain OCT (SD-OCT, Optovue) with particular emphasis on the patient’s epithelial thickness profile. “When the epithelium is not evenly distributed over the cornea, it can induce astigmatism. This usually stems from a tear film problem and needs to be monitored closely to ensure it does not impact on the performance of the premium IOL being implanted,” he said.
In the quest for greater accuracy and predictability with toric lenses, SS-OCT should also prove an invaluable ally as awareness grows of its clinical utility, believes Nino Hirnschall MD, PhD, Vienna Institute for Research in Ocular Surgery, Austria.
“With the SS-OCT we get better images of the entire cornea, the anterior chamber depth and the lens thickness. All this information can be used for a better prediction of the postoperative refractive outcome,” he said.
Dr Mertens agrees with that assessment. “The SS-OCT has become invaluable in my practice. It provides very accurate and predictable readings, it shows whether the patient was fixating at the right point and indicates whether there is a tilt or decentration of the crystalline lens. This is very important to avoid postoperative refractive surprises with these toric lenses,” he said.
Measuring the posterior surface of the cornea to get a clearer picture of the total corneal astigmatism is also very important, said Dr Hirnschall. Furthermore, using Scheimpflug measurements alone for the prediction of the remaining astigmatism after implanting a toric lens may result in a large standard deviation and is not very accurate.
“We have by far the best results with the least standard deviation if we use OCT technology. We showed this in a study looking at the percentage of error deriving from different measurement devices, with Scheimpflug performing worst with a score of 44.6%, then keratometry with 30.0%, topography with 29.2% and finally SS-OCT with 22.7%. OCT and keratometry combined gave the least errors with a score of 18.8%. If we combine different devices that measure different aspects of the cornea, both posterior and anterior, then we can still improve the outcome,” he said.
New high-tech tools are also available to provide digital image guidance for toric IOL alignment, and may offer some advantages over traditional marking and alignment methods.
In a recent prospective comparative study of digital and manual marking methods carried out at the University Hospital of Bordeaux, France, more precise anatomical toric alignment and better reproducibility was found in 25 patients using the VERION™ Image Guided System (Alcon).
While the better alignment with digital marking was not associated with improved clinical outcomes, Cédric Schweitzer MD, PhD told EuroTimes that several factors might explain this apparent parity between the two methods.
“The results would probably have been statistically significant with the inclusion of higher mean preoperative astigmatism. The higher the astigmatism, the more important the clinical impact of a toric IOL misalignment,” said Dr Schweitzer, Department of Ophthalmology, CHU Pellegrin, Bordeaux, France.
Another factor worth mentioning is the importance of total corneal power in the final refractive outcome, said Dr Schweitzer, taking account of anterior and posterior corneal surfaces and the surgically induced astigmatism.
Another recent study of the VERION carried out at the University Eye Clinic Maastricht came to broadly the same conclusion as Dr Schweitzer’s group. While the digital marking device decreased the misalignment by about 50% compared to manual methods, this did not translate into better clinical outcomes.
Dr Nuijts suggests several possible reasons for this, including the fact that the study was conducted using first-generation calculators, which did not take posterior astigmatism into account, and also an early version of the VERION algorithm which has since been updated to take account of effective lens position and posterior corneal astigmatism.
“We know that it is more crucial to have limited misalignment when dealing with patients with high astigmatism than when implanting a lens of 1.0D or 1.5D, because the optical system is quite forgiving up to around five degrees misalignment and not a lot is going to change clinically with 0.3 or 0.4D of residual astigmatism,” he said.
Intraoperative aberrometry measurements in cataract surgery have also become more prevalent in recent years, and are particularly useful for toric IOL implantation according to several surgeons familiar with these devices.
Dr Mertens has been using the Optiwave Refractive Analysis (ORA™ System) intraoperative wavefront aberrometer (Alcon) for the past five years and feels it is a useful addition to his practice.
“The only time I use this device is for toric lenses in virgin eyes or in post-refractive surgery eyes. It is easy to use and it works well. There is a learning curve, however, as the management of intraocular pressure during ORA measurement is vital to get accurate results. A good ocular surface is also critical and the surgeon needs to be careful with the speculum and to ensure that there are no other external sources of pressure on the eye when measuring,” he said.
Dr Nuijts said that, while he was initially sceptical of the concept of intraoperative aberrometry, recent upgrades to the ORA System seem to have improved the accuracy and reproducibility of its measurements.
“There is some progress in the field and the results seem to be improving, especially for those patients at the higher end of the astigmatism spectrum,” he said.
Not all surgeons, however, are convinced of the virtues of intraoperative aberrometry. George Beiko BM, BCh, FRCSC, in private practice in St. Catharines, Canada, believes that the current clinical evidence is too flimsy to justify investing in an intraoperative aberrometer.
“Current presentations and publications do not show any significant impact on determining the power of the astigmatism to correct, but do support some benefit to the alignment of toric IOLs with a about a two-degree improvement in accuracy. However, the cost of this is significant and I believe using IOLs that are more forgiving of misalignment such as the Precizon (Ophtec) and TECNIS® Symfony (Abbott) is more cost effective,” he said.
While much progress has been made in recent years in improving toric IOL outcomes, there is still further room for improvement, according to Dr Beiko.
“I believe that the challenge is still the ability to predict IOL power – currently we are only able to get about 80% of patients within +/-0.50D of targeted outcome. Extended-depth-of-focus lenses and improvements in them should allow us to improve on this,” he said.
For Dr Nuijts, the next challenge is to find ways to personalise the surgically induced astigmatism and posterior astigmatism for every patient.
“Currently we are using average values based on empirical data, large databases etc, but for corneas with high anterior keratometry values the induced astigmatism is also going to be higher. For posterior astigmatism in the small percentage of corneas with 5.0D or 6.0D of astigmatism, we are using a mean level of 0.3 in the calculators when it can in fact be as high as 1.2D or 1.5D. For these special cases we need to come up with a personalised nomogram, and not just one based on average values that will work well for the average cataract patient,” he said.
Rudy MMA Nuijts: email@example.com
Erik Mertens: firstname.lastname@example.org
Nino Hirnschall: email@example.com
Cédric Schweitzer: firstname.lastname@example.org
George Beiko: email@example.com