OSN APAO: 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.

“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 different 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.

Click here to read the full cover story published in Ocular Surgery News APAO Edition, July/August 2015.