With novel approaches to biometry, refractive outcomes of cataract surgery more accurate but still inconsistent

New IOL technologies and heightened patient expectations for precise refractive results have given a great boost to biometry and IOL power calculations. Remarkable improvements have been seen in recent years, and about 1,000 citations for optical biometry now appear in PubMed.

However, “we are still far from perfect,” according to Oliver Findl, MD. “The EUREQUO database, which includes more than 1 million cataract operations, shows that there are a lot of outliers out there. This is the real world: 78% of the eyes are within 1 D. Particularly with short eyes, more than 50% have at least 0.5 D of refractive error.”

Postoperative refraction was analyzed for 17,056 procedures and corneal astigmatism for 7,448 procedures. Emmetropia was targeted in 78.1% of eyes and achieved in 52.7%. Only 43% had less than 1 D of astigmatism.

Similarly, the Swedish National Cataract Register study analyzed the refractive results of more than 17,000 cataract procedures performed between 2008 and 2010 and found that in only 52% of the eyes in which emmetropia was targeted were the expected values achieved. Of the 7,448 eyes in which corneal astigmatism was involved, only 43% had less than 1 D of cylinder after surgery.

Image: Findl O

“The presence in such a large database of patients with comorbidities, such as AMD or glaucoma, may of course have a negative impact on the average results,” Anders Behndig, MD, PhD, said. “However, other factors are involved. One of them is that toric IOLs are not used so often in Sweden. Another one is the use, in a large proportion of cases, of the SRK/T formula, which is a greater source of error compared to the Haigis formula. We should also take into account that ultrasound biometry had to be used in some patients with denser cataracts.”

Optical biometry systems

Optical biometry has been a major step forward toward improved accuracy, as it provides measurements not only of axial length, but also anterior chamber depth and cornea, lens and retinal thickness. Currently available systems include the IOLMaster 700 (Carl Zeiss Meditec) with swept-source biometry and OCT, the AL-Scan (Nidek) optical biometer, the Lenstar LS 900 (Haag-Streit) with dual zone keratometry and optional Placido topography, the Aladdin (Topcon) biometer and Placido topographer, the Galilei G6 Lens Professional (Ziemer) dual Scheimpflug tomographer and Placido topographer with optical biometry, and the OA-2000 (Tomey) optical biometer and topographer.

In a study, Findl and colleagues compared the performance of these systems in 57 eyes of 57 cataract patients, 15 of those with very dense cataract.

“We did three measurements with each device, for a total of about 1,000 measurements. The IOLMaster 700 and the OA-2000 had the highest number of successful scans, 96.7% and 98.7%, respectively. These are the two machines I would recommend if you have patients with dense cataract in your population,” Findl said.

The Galilei system had the largest number of dropouts, with only 78% successful scans in a cataract population.

“[Dropouts are] something that needs to be addressed by the manufacturers,” Findl said.

In the same study, axial length measurements of other systems were compared with the IOLMaster, which is currently the gold standard. An excellent correlation was found among all instruments.

“Among all of the potential sources of error in IOL calculation, axial length is the one that has been most effectively reduced by the current technology. It is with some pride that I say that this technology — optical biometry — that has originated in Vienna at the Institute of Medical Physics has really made a change to patient outcomes worldwide. We did not expect such a change when we performed the first clinical measurements on a large optical bench with our patients in the early 1990s. In this new study comparing the difference new devices, all measurements were similar, as you would expect and hope,” Findl said.

The closest correlation was found between the IOLMaster 700 and the Lenstar LS 900. The AL-Scan had cases with a difference of more than 0.1 mm, which is “also a problem that needs to be addressed,” Findl said.

Swept-source OCT

Swept-source OCT, part of the IOLMaster 700, has been a major step forward, making determination of biometric parameters easier and more accurate.

“With this latest technology, one gets fewer refractive surprises. OCT image-based biometry is useful for visually verifying measurements and for the detection of unusual eye geometries. This improves refractive outcomes,” Pavel Stodulka, MD, PhD, OSN Europe Edition Board Member, said.

He noted that the latest IOLMaster optimizes workflow thanks to its measurement speed, on-board toric IOL power calculation and markerless implantation of toric IOLs.

“To predict postoperative misalignment, which is a major source of error, we fit the parabolas of the surface of the lens before surgery and the same for the IOL after surgery and try to predict lens tilt. We did a study including 62 eyes of 62 patients implanted with a standard lens. Correlation was not so good for the amount of tilt, but orientation of tilt was predicted very well,” Findl said.

“We have to gather more data but hope this will enhance the function and optical performance of IOLs, particularly toric lenses, aspheric lenses and multifocal lenses,” he said.

Intraoperative biometry

Although the latest OCT and Scheimpflug devices have greatly improved precision in anterior chamber depth measurement, postoperative IOL position cannot be determined preoperatively and remains a cause of refractive surprises.

“Where will the lens sit in this eye for this patient? Postoperative [anterior chamber depth] prediction is the biggest source of IOL power calculation error that we have known for many years,” Findl said.

Intraoperative biometry is a promising new concept. The ORA system (Alcon), mounted on the operating microscope, is meant to assist the surgeon in selecting IOL power by refracting the eye and measuring aberrometric changes intraoperatively. While it has gained widespread popularity in the U.S., the ORA has not yet taken off in Europe and seems to be less unanimously accepted by surgeons.

According to Erik L. Mertens, MD, it is a step forward toward achieving accurate results and lowering the re-treatment rate in the premium IOL segment.

“I use the ORA to place toric IOLs in the correct position and also in post-refractive surgery cases,” he said.

Stodulka had the opportunity to use the system for a few days when a demo unit was installed in his center.

“We were able to fine-tune the results slightly, but our conclusion was not to incorporate this technology into our daily routine. It is bulky and slows down surgery with only a limited added value. This does not fit into our high-volume, high-efficacy and efficiency surgical concept. I am waiting for the next generation of devices, which hopefully will be miniaturized and get faster readings,” Stodulka said.

Findl also expressed skepticism. He mentioned a study carried out at Hamburg University, where of the 814 measurements taken, only half were successful and a lot of variability was shown.

“A lot of factors change intraoperative aberrometry. The lid speculum puts pressure on the globe and deforms the cornea. The incision and even the anesthetic drops cause changes. These systems can be misleading and are very expensive,” he said.

In Findl’s opinion, intraoperative OCT is a more effective and promising way of measuring the eye intraoperatively. He personally uses a prototype anterior segment OCT (Visante, Zeiss) attached to the operating microscope, which produces continuous intraoperative OCT videos. He measures the capsule position during surgery after removal of the crystalline lens and before IOL implantation. The measurements correlate well with the postop IOL position.

“The system is not commercially available and technologically demanding, but I am motivated to go on with this project. IOL prediction problems are greatly reduced, also in longer and shorter eyes,” he said.

Improving accuracy with toric IOLs

According to Behndig, pre-existing corneal astigmatism is gradually becoming a major factor precluding emmetropia in modern cataract surgery. In the Swedish National Cataract Register study population, one-third of cases had more than 1 D of corneal astigmatism, and this figure remained largely unaltered after surgery.

“If we used more toric lenses, the number would drop,” he said.

According to Nino Hirnschall, MD, PhD, OSN Europe Edition Board Member, Young Ophthalmologists Section, toric lenses improve astigmatism in most cases, but “results are not always as good as we would like them to be.”

“There are several sources of error. One of them is misalignment, the deviation between the intended axis of the toric IOL and the really measured astigmatism axis. This error might be due to preoperative marking, intraoperative misalignment or postoperative rotation of the IOL,” he said.

However, the main source of error appears to be the measurement of the cornea before surgery, as shown by a study.

“We measured patients’ corneas twice, 1 year apart, and there were differences in astigmatic axis measurement up to 70°, especially in corneas with a low amount of astigmatism, where the astigmatic axis is more difficult to detect,” Hirnschall said.

His advice is to always use different devices to measure the cornea, and if the amount of astigmatism and the axis of astigmatism are similar, the measurements can usually be trusted.

“If there is a discrepancy, the trouble starts. Remember, if you are 10° off, you kind of lose one-third of your astigmatism reduction effect,” he said.

Determining the amount of astigmatism should include measurements of the entire cornea, including the posterior surface, he said.

“One of the used devices should also be able to detect irregular astigmatism, as these cases are very tricky cases and a special calculation is needed. If one can rule out irregular astigmatism and the different devices show similar results concerning amount and axis of astigmatism, the calculation is relatively easy. It can be done in an Excel file, but one can also use the online calculator of the company that provides the toric IOL of choice. If a company’s calculator is used, it is important to check if it takes the surgically induced astigmatism into account and the postoperative anterior chamber depth. Not all of the calculators do so, and this is a potential source of error,” Hirnschall said.

He also recommended that, at the beginning of the process, the same requirements as for non-toric IOLs should be met.

“This may sound simple, but it is important. Before we think about astigmatism reduction, we should think about the refractive outcome in terms of spherical equivalent. If we end up with a refractive surprise of more than 1 D of [spherical equivalent], the astigmatism correction will not be as beneficial as it could be,” Hirnschall said. – by Michela Cimberle

• References:
• Behndig A, et al. J Cataract Refract Surg. 2012;doi:10.1016/j.jcrs.2012.02.035.
• Engren AL, et al. J Cataract Refract Surg. 2013;doi:10.1016/j.jcrs.2012.11.019.
• Hirnschall N, et al. Br J Ophthalmol. 2015;doi: 10.1136/bjophthalmol-2013-304731.
• Hirnschall N, et al. Invest Ophthalmol Vis Sci. 2013;doi:10.1167/iovs.13-11991.
• Hirnschall N, et al. J Refract Surg. 2014;doi:10.3928/1081597X-20140429-01.
• Huelle JO, et al. Br J Ophthalmol. 2014;doi: 10.1136/bjophthalmol-2013-304786.
• Lundström M, et al. J Cataract Refract Surg. 2012;doi:10.1016/j.jcrs.2012.03.006.
• Matz H, et al. Biomed Tech (Berl). 2012;doi:10.1515/bmt-2012-4460.
• Norrby S. J Cataract Refract Surg. 2008;doi:10.1016/j.jcrs.2007.10.031.
• Preussner PR, et al. J Cataract Refract Surg. 2004;doi:10.1016/j.jcrs.2004.07.004.
• Stringham J, et al. J Cataract Refract Surg. 2012;doi:10.1016/j.jcrs.2011.09.039.

• For more information:
• Anders Behndig, MD, PhD, can be reached at Department of Clinical Science, Ophthalmology, Umeå University Hospital, SE-901 85 Umeå, Sweden; email: anders.behndig@ophthal.umu.se.
• Oliver Findl, MD, can be reached at VIROS, Department of Ophthalmology, Hanusch Hospital, Heinrich Collin-Straße 30 1140, Vienna, Austria; email: oliver@findl.at.
• Nino Hirnschall, MD, PhD, can be reached at VIROS, Hanusch Krankenhaus, Heinrich-Collin Straße 30, 1140 Vienna, Austria; email: nino.hirnschall@googlemail.com.
• Erik L. Mertens, MD, can be reached at Eye Center Medipolis, Boomsesteenweg 223, 2610 Wilrijk, Belgium; email: e.mertens@medipolis.be.
• Pavel Stodulka, MD, PhD, is head eye surgeon at the Gemini Eye Clinic in Prague, Czech Republic. He can be reached at email: stodulka@lasik.cz.

Disclosures: Behndig reports no relevant financial disclosures. Findl reports he is a consultant to Abbott Medical Optics, Bausch + Lomb, Carl Zeiss Meditec, Croma and Hoya and a patent assignee of intraOP OCT. Hirnschall reports he is a patent assignee of intraOP OCT. Mertens reports he is a consultant for STAAR Surgical, Ophtec, PhysIOL and Bausch + Lomb. no relevant financial disclosures. Stodulka reports he is a consultant to Bausch + Lomb.

Is intraoperative refractive biometry a worthwhile investment for the cataract surgeon?

For the premium practice, it is a must-have

I believe that in a premium practice, intraoperative refractive biometry with the ORA system (Alcon) is a service we should be able to provide. There is no need and no time to use it routinely, but it is an extremely good tool in special cases, such as eyes that have previously undergone PRK or LASIK and in short or long eyes, in which accurate IOL power calculation is a challenge and no empiric formula can deliver what we want. It is equally useful in eyes implanted with phakic IOLs, in which measurements are difficult even with partial interferometry systems such as the Lenstar (Haag-Streit) and IOLMaster (Carl Zeiss Meditec), as well as in silicone oil-filled eyes or eyes with corneal irregularities. In pediatric cataract, it is a superb asset.

There is a mistake some surgeons make when using the ORA, which is to hydrate and pressurize the eye with balanced salt solution. I initially did that and then realized it is better to homogenously inject a viscous ophthalmic viscosurgical device because you do not hydrate the incision, can perfectly achieve the required IOP and have no fluid egress during measurement. This is one of the key points for good results and time optimization.

Indeed, some additional time is required when you do a procedure with the ORA. If you want to check on the changes induced by a refractive procedure such as arcuate incisions or correct the axis of a toric implant, you have to add about 5 minutes to your standard. It decreases your working space from the microscope to the eye, and you have to attach a sterile cover on the ORA at the microscope. You also need a second person, trained to stand on your side and use the touch screen. The ORA is a time investment and a money investment. But if you can improve predictability in the group of patients in which predictability is normally low, this investment is worth every cent.

Only very few people use ORA in Europe. In Germany, I was the first to adopt it, and the breakthrough for me was the VerifEye software and hardware upgrade, offering continuous, nonstop measurements that you can see on the screen. With the latest upgrade, the system is now much faster, versatile and specialty-driven.

H. Burkhard Dick, MD, PhD, is an OSN Europe Edition Board Member and chairman and head of the University Eye Clinic Bochum, Germany. Disclosure: Dick reports no relevant financial disclosures.

Reliability, cost-effectiveness have not been proven

Intraocular biometry is indeed a very interesting and attractive concept. A different issue is whether it solves problems or is reliable enough to be accepted or converted into standard practice.

The problem is that the condition of the eye post-cataract or refractive lensectomy is very diverse and influenced by many factors. The cornea is affected by the procedure in thickness and geometry. IOP plays an important role. The external influence of instruments such as the speculum and the eyelid configuration of the patient forced by local anesthesia are many times, indeed, an added variable to consider. The condition of the pupil is variable. The position of the lens and, consequently, the refractive results are not stable. They depend on the depth of the anterior chamber, which is affected by surgical maneuvers, by the quality of the surgery and by changes in the capsular bag that occur postoperatively in the immediate 24 hours and in the first 3 months. All of these variables make any measurement performed intraoperatively substantially unreliable.

The value of intraoperative biometry, and particularly the ORA, is at present doubtful. In my opinion, and from the experience I have had with it, it is not cost-effective, it is in most cases unreliable, and it only offers some value in the study of the astigmatism axis for the IOL. What we get is just the total information from the refraction of the eye, and issues such as the changes that happen in the anterior and posterior corneal surface are part of this measurement. How this matches with the toric IOL position is more than debatable. It might not be the final position of the eye, even though it might be orientative. Studies should correlate the intraoperative measurements with measurements performed postoperatively and at 1 and 3 months. Initial studies seem to be promising but are still too few and in small cohorts of patients to support evidence in favor of this technology.

Jorge L. Alió, MD, PhD, is an OSN Europe Edition Board Member and medical director, Vissum Corporation, Alicante, Spain. Disclosure: Alió reports no relevant financial disclosures.