Financial Disclosure
I have a financial interest with the following
companies:
Abbott Medical Optics
Alcon
Calhoun Vision
NuLens
Optimedica
Optivue
IOL power calculations in
post-LASIK/PRK eyes
Douglas D. Koch, M.D.
Cullen Eye Institute,
Baylor College of Medicine,
Houston, TX
Challenges

Difficulties in determining true corneal
refractive power



Keratometric inaccuracy
Invalid use of effective refractive index of
cornea (1.3375)
Problems in 3rd and 4th generation IOL
formulas


Inaccurate estimation of ELP
Exception: Haigis formula
So many formulas. . So we developed:
http://www.ascrs.org/
IOL power calculation
Prior myopic-LASIK/PRK
Double-K
Holladay 1
and Haigis-L
formulas
3 categories of
formulas
3 categories
Traditionally
“Gold” standard
KEY – accurate
historical data
Data error 1:1
ratio
Use a fraction
of ∆MR
Data error ↓
to 20 – 30%
Rely only on
current data
Pop-up
windows
explain
methods
used
Prior
hyperopicLASIK/PRK
Prior RK
Monthly visits to the calculator in 2010
9,000
8,000
7,000
8,249
7,853
7,218
6,173
6,570
7,666
6,758 6,825
6,369
6,791
7,257
7,105
6,000
5,000
4,000
3,000
2,000
1,000
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Patients


2 study centers
Consecutive cases of IOL implantation in
eyes with prior myopic-LASIK


SN60WF
72 eyes of 57 patients included


Mean age: 58 ± 8 years (range 42 to 77
years)
Myopic LASIK correction: 5.10 ± 2.55 D
(range 0.98 to 11.21 D)
Methods

IOL prediction error



= IOL implanted – IOL calculated
Negative value  myopic results
Consistency of prediction performance

F-test for variances
A
-2.0
Average IOL power
A
Haigis-L
Shammas
2.0
Wang-Koch-Maloney
A
Modified-Masket
A
Masket
Adjusted Atlas0-3
A
A
Adjusted EffRP
4.0
Corneal Bypass
-4.0
Feiz-Mannis
Clinical History
S
A
A
A
A
A
0.0
A
A
AA
A
A
Variances of IOL prediction errors (SD2)
- consistency of performance
*
Pre-LASIK Ks + ∆ MR
Clinical History
Feiz-Mannis
Corneal Bypass
2.06
2.53
1.99
∆ MR
Adjusted EffRP
Adjusted Atlas0-3
Masket
Modified-Masket
0.70
0.68
0.63
0.62
No prior data
Wang-Koch-Maloney
0.68
Shammas
0.66
Haigis-L
0.66
* Significant differences (all P<0.05 with
Bonferroni correction)
Refractive prediction error
± 0.5
D
± 1.0 D
Pre-LASIK Ks + ∆MR*
Clinical History
Feiz-Mannis
Corneal Bypass
44
37
37
69
60
68
∆MR
Adjusted EffRP
Adjusted Atlas0-3
Masket
Modified-Masket
62
64
57
67
86
90
91
90
Methods
Proposed UK NHS
benchmark in normal
eyes*:
85% ±1.0 D
55% ±0.5 D
Met
benchmark
in normal
eyes but
well below
latest
standards
No prior data
Wang-Koch-Maloney
58
96
Shammas
60
90
Haigis-L
60 methods
94(P<0.05). Gale RP, et al.
*Significant lower % with historical
Benchmark standards for refractive outcomes after NHS cataract
surgery. Eye. 2009;23:149-52
Summary

Using double-K Holladay 1 formula

Greater prediction errors and variances with
methods requiring Pre-LASIK Ks and ∆MR


Use 100% of historical data
Superior and essentially equivalent results
with:


Methods using a fraction of ∆MR and
Methods using no prior data
Optical coherence tomography (OCT)

RTVue-CAM: an Fourier domain OCT
system for both retinal and corneal
imaging
RTVue with CAM
module
Net Corneal Power (NCP):
Combines anterior & posterior
curvature measurements from OCT
meridional scans
1.5mm
1.5mm
n0 = 1
D
n1 = 1.376
Ra
Rp
n2 = 1.336
Kp 
n2  n1
Rp
Ka 
n1  n0
Ra
Evaluation of OCT-based formula

IOL power calculation in post-LASIK
eyes
 12
eyes at Cullen Eye Institute
 8 eyes at Doheny Eye Institute
 Refractive correction: -4.04 ± 3.60 D
(range -0.88 to -9.81 D)
OCT-based IOL power formula
ELP = 0.711 * (AL – ACD) – 0.25 * Pp + 0.623 * ALadj + pACD – 8.11
Where
AL = axial eye length (mm)
ACD = Anterior chamber depth (mm)
Pp = posterior corneal power (D)
ALadj = sqrt(AL)
if AL < 24.4mm
sqrt(AL+0.8*(AL-24.4)),
if AL > 24.4mm
pACD = personalized ACD (ACD-constant)
*Tang M, Li Y, Huang D. An Intraocular Lens Power Calculation Formula Based on Optical Coherence
Tomography: a Pilot Study. J Refract Surg. 2010;26(6):430-437
Refractive prediction error
Keratometry
Method
Best IOL
Formula
Prediction
Error (D)
Range
(D)
MAE
(D)
Adjusted
MAE (D)
IOL-Master
Haigis-L
-0.23 ±
0.83
(-1.93, 1.30)
0.66
0.65*
OCT
OCTbased
-0.01 ±
0.70
(-0.85, 1.79)
0.56
0.56*
*P=0.65, n = 20 eyes of 15 subjects.
Refractive prediction error
Haigis-L
OCT formula
8
Within 0.5D:
•Haigis-L: 11/20
•OCT: 10/20
# of eyes
6
4
Within 1D:
•Haigis-L: 15/20
•OCT: 19/20
2
0
Predicted – Actual Postoperative Refraction (D)
Summary

Limitation:



Small numbers
Performance of OCT-based IOL formula was
not compared to many methods on the
ASCRS calculator
Further studies desirable
Recent study


Accuracy of Galilei in IOL power
calculation in eyes with prior myopic
LASIK/PRK
Consecutive cases of IOL implantation
between April 08 to Feb. 11
Patients

19 eyes of 16 patients had all
historical data
LASIK correction: 4.28 ± 2.61
D (range 0.88 to 8.50 D)
 Myopic
Refractive
MAE with all methods (n=19)
1.2
1.0
0.99
0.94
0.93
0.78
0.65
0.6
 
0.52

0.57 0.57
0.75
0.72 0.70

0.47
0.42 0.44
0.4
Galilei
Significant greater MAE with methods using pre-LASIK
Ks and ∆MR than those with  (all P<0.05)
TCP-5mm
TCP-4mm
TCP-3mm
TCP-2mm
Haigis-L
Shammas
Wang-Koch-Maloney
Modified-Masket
Masket
Adjusted Atlas0-3
Adjusted EffRP
Corneal Bypass
0.0
Feiz-Mannis
0.2
Clinical History
MAE (D)
0.8
Refractive prediction error with all methods
UK NHS
(n=19)
100
89
90
79
74
68
74
74
74
58
68
58
58
53
55%
±0.5 D
53
47
50
42
32
32
32
32
32
26
30
21
20
Galilei
TCP-5mm
TCP-4mm
TCP-3mm
TCP-2mm
Haigis-L
Shammas
Wang-Koch-Maloney
Modified-Masket
Masket
Adjusted Atlas0-3
Adjusted EffRP
Corneal Bypass
Feiz-Mannis
10
0
85%
±1.0 D
63
Clinical History
% of eyes
79
+/- 0.5 D
+/- 1.0D
70
40
89
84
79
80
60
benchmark
95
Accuracy of IOL power
calculation in eyes with prior
RK
Purpose


Because RK eyes have variable front and
back curvatures, IOL calcs are especially
challenging
To evaluate the accuracy of 4 devices for
calculating corneal power for IOL
calculations in RK eyes undergoing
cataract surgery

IOLMaster, EyeSys, Atlas, Galilei
Patients

Consecutive cases of IOL implantation
between April 08 to February 11

27 eyes of 18 patients, age 47 to 79 years
Refractive mean absolute error (MAE)
with different devices
0.8
0.7
0.65
0.67
0.66
0.58
0.6
MAE (D)
0.5
0.4
0.3
0.2
0.1
0.0
EyeSys EffRP
IOLMasterK
Atlaszone0-3
TCPannuli1-4
Galilei TCPannuli1-4 tended to produce smallest
MAE (all P>0.05).
Refractive prediction error
+/- 0.50 D
85
+/- 1.0 D
90
UK NHS
benchmark
85
85
78
80
85%
±1.0 D
70
59
% of eyes
60
55%
±0.5 D
52
50
40
33
30
30
20
10
0
EyeSys EffRP
IOLMaster K
Atlaszone0-3
TCPannuli1-4
Proposed benchmark for normal eyes: Gale RP, et al. Benchmark
standards for refractive outcomes after NHS cataract surgery. Eye.
2009;23:149-52.
Galilei
Needs further work to improve IOL
calculations after LASIK
 Helpful in eyes that have undergone
radial keratotomy

Thank you for your attention