1. 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

2. 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

3. 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.

4. 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

5. 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.

6. 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

7. 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.

8. 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

9. 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

10. 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

11. 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.

12. Method ▪ Design : Retrospective chart review
▪ Setting : Seoul St. Mary’s Hospital
▪ Patients
- Between September 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.

13. 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

14. Protocols for studies of Intraocular Lens Formula Accuracy
Am J Ophthalmol Sep;160(3):
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

15. 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

16. 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.

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

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

19. 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

20. 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.

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

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

23. 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

24. 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.

25. 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.

26. Thanks