Aug 11, 2017 Comparison of predictive accuracy on Partial coherence interferometry (PCI) and swpt-source optical coherence tomographry (SS-OCT) Choun-Ki Joo, MD, PhD Seoul St. Mary’s Hospital Catholic University of Korea, College of Medicine Catholic Institute for Visual Science

Introduction Most of the modern day formulae are based upon the theoretical equation formulated by Fyoderov and its modifications.  P = (1336/[AL-ELP]) – (1336/[1336/{1000/([1000/DPostRx] - V) + K} - ELP]) Net corneal power (K), Axial length (AL), IOL power (P), Effective lens position (ELP), Desired refraction (DPostRx), Vertex distance (V) The prediction of effective lens position (ELP) is the most important process in IOL power calculation. Shammas et al. JCRS 2015

The third-generation formulas Introduction The third-generation formulas The most popular for calculating intraocular lens (IOL) power in cataract surgery Estimate postoperative effective lens position (ELP) by using various preoperative biometric variables such as central corneal power and axial length Haigis, Hoffer Q, Holladay 1, and the SRK/T formulas. Comparison of immersion ultrasound biometry and partial coherence interferometry for intraocular lens calculation according to Haigis Graefes Arch Clin Exp Ophthalmol. 2000;238:765–73. Calculation of intraocular lens power: a review. Acta Ophthalmol Scand. 2007;85:472–85.

The third-generation formulas Introduction The third-generation formulas anterior corneal power (K) anterior corneal radius of curvature (R) axial length (AL) anterior chamber depth (ACD) : the Haigis formula Formula Variables for ELP prediction Haigis ACD,AL Hoffer Q pACD, K, AL Holladay 1 SF(surgeon factor), K, AL SRK/T A(A-constant), K, AL

Major sources of prediction error for the IOL power Norrby S. Sources of error in intraocular lens power calculation. J Cataract Refract Surg 2008; 34: 368–376.

Errors of third generation formulas by ocular biometric factors Different consideration of variables (in each formula) Disparities in ELP estimation Formula Variables for ELP prediction Haigis ACD,AL Hoffer Q pACD, K, AL Holladay 1 SF(surgeon factor), K, AL SRK/T A(A-constant), K, AL Disparities in predicted postoperative refractions 각 formula 에서 고려하는것이 각각 다르기때문에 ELP estimation 이 달라지고, 이때문에 예상하는 post op refraction 이 달라지게 됨. 그렇다면 어떤 ocular biometry 가 각각 공식의 예측에 영향을 미칠까 ? The effect of ocular biometric factors on the accuracy of various IOL power calculation formulas BMC Ophthalmology (2017) 17:62

PCI(Partial Coherence Interferometry) Devices PCI(Partial Coherence Interferometry) Axial length 780 nm laser diode infrared light Anterior chamber depth lateral slit-illumination Corneal power 6 points at 2.5mm zone Fail in determining the AL in the presence of a dense nuclear or posterior subcapsular cataract. Because The signal from the retina becomes attenuated or blocked due to the light scattering inside the lens.

Devices SS-OCT (swept sources Optical coherence tomography) Axial length 1050~1080 nm swept laser source Anterior chamber depth Corneal power 4 points at 3.0 mm zone extended axial range collection of 2-dimensional data -> capturing full eye Improve the success ratio in measuring the AL as well as the repeatability of its measurements whereas the PCI unit measures ACD through a lateral slit illumination 2-dimensional display by the OCT unit allows a more precise ACD measurement independent of the subject's fixation angle

SS-OCT (swept sources Optical coherence tomography) The Argos (Movu, Inc.), collect 2-dimensional OCT data of the full eye (SS-OCT) high lateral resolution and axial resolution measure not only the AL and the ACD but also the central corneal thickness (CCT), aqueous depth, lens thickness, pupil size, and corneal diameter. high-speed measurement (~30x faster than optical biometry) Even in dense cataract

Repeatability and Reproducibility of the SS-OCT measurements Measurements with the new SS-OCT biometer were repeatable and reproducible N=42 Bland-Altman plot Comparison of PCI and SS-OCT Axial length measurements comparable to PCI with a faster and higher acquisition rate even in the presence of a dense nuclear or posterior subcapsular cataract

The purpose of our study To evaluate the AL, ACD, and K measurements with the results obtained with the PCI and SS-OCT biometers To compare the refractive outcomes when 2 optical biometers were applied.

Method ▪ Design : Retrospective chart review ▪ Setting : Seoul St. Mary’s Hospital ▪ Patients - Between September 2016 and Mar 2017 - 153 patients (153 eyes) - 1 type of IOL (Precizon monofocal 560, Ophtec, Groningen, Netherland) was implanted in the bag. - Refractive outcomes were measured at preoperatively and 3months postoperatively.

Method ▪ Examination - Pre operative value : PCI versus SS-OCT Axial length (mm) Keratometric value (diopter) Anterior chamber depth (mm) - Post operative Manifest refraction Mean error (diopter) Mean absolute error (diopter) - MAE Median absolute error (diopter) - MedAE

Protocols for studies of Intraocular Lens Formula Accuracy Am J Ophthalmol. 2015 Sep;160(3):403-405 Hoffer KJ, Aramberri J, Haigis W, Olsen T, Savini G, Shammas HJ, Bentow S. Optimization (ME zeroed out) Comparing not MAEs but median AE Using only 1eye Using 1~2 IOL 3months postoperatively Retrospectively personalized IOL constants Optimized IOL constants and personlaized IOL constants for the PCI and SS-OCT

Patient characteristics Result Patient characteristics Eyes 153 Preoperative UDVA(logMAR) 0.59±0.42 CDVA(logMAR) 0.43±0.45 Spherical equivalent(D) -1.62±4.75 Age (year) 69.09±9.69 IOL power (D) 18.07±5.43 Postoperative 0.16±0.20 0.02±0.06 -1.20±1.03

Comparison of parameter measurements between the 2 biometers Result Comparison of parameter measurements between the 2 biometers N=153 The SS-OCT’s ocular biometry measurements shows similar biometric measurements to those of conventional biometers.

Intraclass correlation coefficient and 95% CI Result Intraclass correlation coefficient and 95% CI Measurements with the new SS-OCT biometer were repeatable and reproducible

Correlation Result AL Kmean ACD y = 0.982x + 0.757 R2 = 0.967

Result Refractive outcomes at 3months postoperatively Mean error, Mean absolute error, Median absolute error PCI SS-OCT Barret-Universal II ME(D) -0.38±0.44 -0.43±0.45 MAE(D) 0.49±0.33 0.51±0.35 MedAE(D) 0.44 0.50 Haigis -0.07±0.45 -0.13±0.44 0.36±0.28 0.29 0.30 HofferQ -0.16±0.48 -0.20±0.46 0.41±0.28 0.42±0.28 0.40 0.39 SRK/T -0.29±0.49 -0.33±0.50 0.47±0.33 0.49±0.34 0.41 0.46 T2 -0.29±0.47 -0.33±0.48 0.45±0.32 0.48±0.33 When the optimized IOL constants were applied

Result Refractive outcomes at 3months postoperatively Mean error, Mean absolute error, Median absolute error When the retrospectively personalized IOL constants were applied PCI SS-OCT Barret-Universal II ME(D) 00±0.44 0.00±0.45 MAE(D) 0.34±0.29 0.36±0.27 MedAE(D) 0.27 0.32 Haigis 0.00±0.44 0.35±0.29 0.34±0.27 0.28 0.31 HofferQ 0.00±0.48 0.000±0.46 0.39±0.27 0.37±0.27 0.35 SRK/T 0.00±0.49 0.00±0.50 0.38±0.31 0.39±0.31 0.33 T2 0.00±0.47 0.37±0.28 0.38±0.29 0.34 After personalization, the predictive accuracies of the two optical biometers are almost the same overall. In addition, the need for optimization is greater in SS-OCT.

MedAE in each formula in subgroup of Axial length Result MedAE in each formula in subgroup of Axial length SRK/T Hoffer Q T2

MedAE in each formula in subgroup of Axial length Result MedAE in each formula in subgroup of Axial length Barret-Universal II

Best formula in each subgrops(AL) Result Best formula in each subgrops(AL) HofferQ Haigis Haigis BU II BU II BU II BU II HofferQ

Conclusion The recently introduced SS-OCT shows similar biometric measurements to those of conventional biometers. After personalization, the predictive accuracies of the two optical biometers are almost the same overall. In addition, the need for optimization is greater in SS-OCT. In medium-long eyes, the predictive accuracy of the SS-OCT is higher, but in the shorter or longer eyes, the PCI tend to be more accurate. The Barret-Universal II formula : one of fifth generation formula, seems to be more appropriate for PCI.

Discussion So far, PCI is thought to be more accurate in IOL power prediction. However, the SS-OCT method has the advantage of faster and higher acquisition rate, even in the presence of a dense nuclear or posterior subcapsular cataract. More accurate ACD measurement being able to get image of whole eye Lens thickness Aqueous depth Central corneal thickness Corneal diameter Not only can you get accurate measurements, but ultimately, it can be a good tool for ELP prediction.

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