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Lee, Chung, Chung, and Kee: Comparison of Intraocular Lens Power Calculation Methods for Cataract Surgery after Refractive Surgery: A Retrospective Surgery
Original Article

J Korean Ophthalmol Soc 2010;51(2):180-187.

Published online: 7 September 2010

DOI: https://doi.org/10.3341/jkos.2010.51.2.180

Comparison of Intraocular Lens Power Calculation Methods for Cataract Surgery after Refractive Surgery: A Retrospective Surgery

Myoung-Ok Lee, MD, Tae-Young Chung, MD, PhD, Eui-Sang Chung, MD, PhD, Chang Won Kee, MD, PhD

Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea

Address reprint requests to Chang Won Kee, MD, PhD Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine #50 Ilwon-dong, Gangnam-gu, Seoul 135-710, Korea Tel: 82-2-3410-3564, Fax: 82-2-3410-0074, E-mail: ckee@skku.edu

Received 21 October 2009       Accepted 15 December 2009

Copyright © 2010 Korean Ophthalmological Society

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

To investigate the predictability of and propose guidelines for intraocular lens (IOL) power calculation in postcataract surgery patients with prior corneal refractive surgery and suggest the guideline.

Methods

Medical records of 18 eyes of 16 patients were retrospectively evaluated for IOL power calculation predictability using three combinations of methods: 1) clinical history method, modified Maloney method, and the Feiz-Mannis method; 2) single-K formula versus double-K formula; and 3) Three IOL formulas (SRK/T, Holladay 1, and Hoffer Q).

Results

The clinical history method using the single-K formula with the SRK/T and Holliday 1 formula showed the best predictability, with an absolute error of 0.60±0.63 D and 0.74±0.60 D, respectively. The Feiz-Mannis method showed a tendency of myopic prediction, whereas the modified Maloney method showed a tendency of hyperopic prediction, especially in the patients with myopia more than 7 D prior to the refractive surgery. The double-K formula, when compared to the single-K formula, prevented hyperopic prediction when used with the clinical history method or modified Maloney method.

Conclusions

IOL power calculation using the clinical history method with SRK/T or Holliday 1 formula showed the best predictability in patients after corneal refractive surgery. IOL power calculation using the modified Maloney method, however, because of the hyperopic prediction tendency, should be used cautiously, especially for patients with myopia of 7 D or more prior to the refractive surgery.

Keywords: Cataract, Corneal refractive surgery, IOL power calculation

References

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Table 1.
Methods of intraocular lens power calculation after refractive surgery
Method Calculation
Clinical history mothod K*=preop K+preop R†-postop R
Feiz-Mannis method IOL power=preop IOL power+(postop R-preop R)/0.7
Modified Maloney method K=(central topographic power×[376/337.5])-6.1

* K=keratometry

† R=refraction

Table 2.
Demographic data for eyes with cataract surgery after refractive surgery
Eyes
Age (years) 52.56±11.38
Axial length (mm) 27.82±1.84
Implanted Intraocular lens power (D*) 18.41±2.33
K-value before refractive surgery by manual keratometer (D) 43.28±1.47
K-value after refractive surgery by manual keratometer (D) 38.49±1.36
3-mm zone K-value after refractive surgery by Orbscan (D) 38.65±1.23
Spherical equivalent before refractive surgery (D) −7.83±3.76
Spherical equivalent after refractive surgery (D) −2.51±2.34
Spherical equivalent after cataract surgery (D) −0.89±1.39

* D=diopter

Table 3.
Mean prediction error and absolute prediction error (in diopters) according to different methods for cataract surgery after refractive surgery
Single K
 Feiz-Mannis method Double K
Clinical history method Modified Maloney method Clinical history method Modified Maloney method
SRK/T
 Prediction error 0.11±0.93 0.85±2.21 −1.12±2.27 −0.95±0.92 −0.05±2.27
 Absolute error 0.60±0.63 1.56±1.54 1.73±1.47 1.02±0.69 1.67±1.43
Holladay 1
 Prediction error 0.05±0.94 0.69±2.32 −1.23±2.32 −0.67±1.02 0.08±2.27
 Absolute error 0.74±0.60 1.89±1.56 1.93±1.37 0.87±0.65 1.76±1.42
HofferQ
 Prediction error −1.01±1.01 −0.15±2.13 −1.65±2.21 −1.32±1.21 −0.48±2.42
 Absolute error 1.31±0.84 1.91±1.10 2.47±1.08 1.52±1.27 1.73±1.62
Table 4.
P-value of prediction error and absolute prediction error (in diopters) according to different methods for cataract surgery after refractive surgery
CHM* vs. MMM†(with SK) CHM* (with SK) vs. FMM‡ MMM*(with SK) vs. FMM‡ CHM* vs. MMM† (with DK) CHM* (with DK) vs. FMM‡ MMM* (with DK) vs. FMM‡ SK vs. DK (with CHM*) SK vs. DK (with MMM†)
SRK/T
 P§ error 0.03 0.01 0.01 0.05 0.67 0.03 0.03 0.03
 A∏ error 0.02 0.03 0.63 0.13 0.17 0.85 0.31 0.81
Holladay 1
 P§ error 0.03 0.01 0.01 0.07 0.31 0.02 0.04 0.04
 A∏ error 0.01 0.02 0.92 0.05 0.08 0.87 0.74 0.73
HofferQ
 P§ error 0.02 0.03 0.01 0.03 0.56 0.02 0.43 0.13
 A∏ error 0.23 0.02 0.59 0.63 0.05 0.72 0.58 0.76

* CHM=clinical history method

† MMM=modified Maloney method

‡ FMM=Feiz-Mannis method

§ P=prediction error

∏ A= absolute prediction error.

The mean prediction errors and absolute prediction errors produced by different methods were compared using the paired t test and two-way ANOVA.

Table 5.
P-value of prediction error and absolute prediction error (in diopters) according to intraocular lens (IOL) formulas for cataract surgery after refractive surgery
Single K
 Feiz-Mannis method Double K
Clinical history method Modified Maloney method Clinical history method Modified Maloney method
SRK/T vs. Holladay 1
 Prediction error 0.77 0.68 0.79 0.53 0.86
 Absolute error 0.76 0.63 0.72 0.71 0.85
Holladay 1 vs. Hoffer Q
 Prediction error 0.08 0.06 0.59 0.26 0.39
 Absolute error 0.41 0.87 0.53 0.29 0.95
HofferQ vs. SRK/T
 Prediction error 0.04 0.04 0.36 0.38 0.31
 Absolute error 0.32 0.61 0.41 0.35 0.81

The mean prediction errors and absolute prediction errors produced by IOL formulas were compared using the two-way ANOVA.

Table 6.
Range of prediction error (in diopters) according to different methods for cataract surgery after refractive surgery
Single K
 Feiz-Mannis method Double K
Clinical history method Modified Maloney method Clinical history method Modified Maloney method
SRK/T
  <-0.5 D 3 2 6 4 3
 -0.5 to +0.5 D 13 9 11 14 12
  > +0.5 D 2 7 1 0 3
Holladay 1
  <-0.5 D 4 3 7 5 3
 -0.5 to +0.5 D 12 19 11 13 12
  > +0.5D 2 6 0 0 3
HofferQ
  <-0.5 D 5 3 7 5 4
 -0.5 to +0.5 D 13 10 11 13 12
  > +0.5 D 0 5 0 0 2
Table 7.
Comparison of mean prediction error and absolute prediction error (in diopters) according to degree of myopia before refractive surgery
SRK/T Single K
 p-value Feiz-Mannis method Double K
 p-value
Clinical history method Modified Maloney methods Clinical history method Modified Maloney methods
Prediction error
 Myopia <-7 D (n=10) 0.15±0.91 −0.28±0.58 0.68 −0.73±1.37 −0.85±1.15 −1.05±1.19 0.69
 Myopia ≥-7 D (n=8) −0.21±1.71 2.45±1.93 0.01 −0.07±3.52 −0.97±0.67 2.06±2.83 0.01
    p-value 0.54 0.01 0.44 0.76 0.01
Absolute error
 Myopia <-7 D (n=10) 0.44±0.63 0.58±0.47 0.78 1.28±1.04 0.99±0.83 1.13±0.61 0.71
 Myopia ≥-7 D (n=8) 0.75±1.35 2.61±1.76 0.01 2.32±1.76 1.07±0.57 2.31±2.31 0.02
    p-value 0.46 0.01 0.12 0.83 0.18

The cut-off value of myopia was based on a minimum P-value approach.

The prediction errors and absolute prediction errors were compared using the paired t test and two-way ANOVA.

Appendix 1.
Aramberri double-K SRK formula
Double-K SRK/T Formula
Equation 1: Preoperative corneal radius of curvature:
     r pre=337.5/Kpre
Equation 2: Corrected axial length (LCOR):
     If L≤24.2, LCOR=L
     If L>24.2, LCOR=-3.446+1.716× L-0.0237× L2
Equation 3: Computed corneal width (Cw):
     Cw=-5.41+0.58412× LCOR+0.098× Kpre
Equation 4: Corneal height (H):
     H=r pre_Sqrt [rpre2_(Cw2/4)]
Equation 5: Offset value:
     Offset=ACD const-3.336
Equation 6: Estimated postoperative ELP (ACD):
     ACD es t=H+Offset
Equation 7: Constants:
     V=12; n a=1.336; n c=1.333; n c m1=0.333
Equation 8: Retinal thickness (RETHICK) and optical axial length (LOPT):
     RETHICK=0.65696–0.02029× L
     LOPT=L+RETHICK
Equation 9: Postoperative corneal radius of curvature:
     r post=337.5/Kpost
Equation 10: Emmetropia IOL power (IOLemme):
     IOL emme=[1000× n a×(n a× r post-n c m1× LOPT)]/[(LOPT_ACD est)×(n a× r post_n c m1× ACD est)]
Equation 11: Conversion from IOL A-constant to IOL ACD constant:
     ACD const=0.62467× A-constant-68.747
Variables
L=axial length; Kpre=pre refractive surgery K-value; Kpost=post refractive surgery K-value; ACD const=IOL constant (can be computed from A-constant).
Appendix 2.
Double-K Holladay 1 formula
Double-K Holladay 1 Formula
Equation 1:
     Rag=Rpre; if Rpre<7.0 mm, Rag=7.0 mm:
Equation 2: Anterior chamber diameter, angle to angle
     AG=1.25×(AL/23.45); If AG>13.5 mm, AG=13.5 mm
Equation 3: Anatomic anterior chamber depth
     ACD=Z 0.56+Rag-(SQRT{ABS[RAG2-(AG2/4)]})
Equation 4: Optical anterior chamber depth
     OACD=ACD+SF
Equation 5: Intraocular lens power from desired postoperative refraction
     IOL=1000× n a×{n a× R post-(n c-1)× Alm-0.001× Ref×[V×(n a× R post-(n c-1)× Alm)+(Alm× R post)]}/
       (Alm-OACD)×{(n a× R post)-(n c-1)× OACD-0.001× Ref×[V×(n a× R post-(n c-1)× OACD)+OACD× R post]}
Equation 6: Resultant refraction from IOL power
     Ref=[1000× n a×[n a× R post-(n c-1)× Alm]-IOL×(Alm-OACD)×{(n a× R post)-[(n c-1)× OACD]} /
       n a×{V×[n a× R post-(n c-1)× Alm]+(Alm× R post)}-0.001× IOL×(Alm-OACD)×{[V×(n a× R post-(n c-1)×
       OACD)]+(OACD× R post)}
Measured Values
   K pre=average K-reading before radial keratotomy (RK) (diopters[D])
   K post=average K-reading after RK and before cataract surgery (diopters)
   R pre= average corneal radius (mm)=337.5/Kpre
   R post=average corneal radius (mm)=337.5/Kpost
   AL=average axial length (AL) (mm)
Chosen Values
   V=vertex distance of pseudophakic spectacles (mm); default=12.0 mm
   Ref=desired postoperative spheroequivalent refraction (D)
   SF=surgeon factor (mm)
   SF=0.5663× A constant-65.6
Other Variables
   AG=anterior chamber diameter from angle to angle (mm)
   ACD=anatomic anterior chamber depth (mm)
   Alm=modified AL (mm)=measured AL(AL)+retinal thickness factor (RT)
Appendix 3.
Double-K Hoffer Q Formula
Double-K modification of the Hoffer Q Formula
Equation 1: Anterior chamber depth
     ACD=pACD+0.3(AL-23.5)+tan(K pre-LASIK)2+(0.1× M×[23.5_AL]2_[tan{0.1(G-AL)2}])-0.99166
     M: if AL≤23.00, M=1; if AL>23mm, M=-1
     G: if AL≤23.00, G=28.00 mm; if AL>23 mm, G=23.5 mm
     If AL>31, AL=31.0; if AL<18.5, AL=18.5
Equation 2: Refractive error at corneal plane
     R=Rx⁄(1–0.012 Rx)
Equation 3: Intraocular lens power
     P=(1336⁄[AL-ACD-0.05])-(1.336⁄[{1.336⁄(K post-LASIK +R)}-{(ACD+0.05)⁄1000}])
Equation 4: Refractive error
     R=(1.336⁄[1.336⁄{1336 ⁄(AL-ACD-0.05)-P}+{ACD+0.05}⁄1000])-K post-LASIK
     Rx=R⁄(1+0.012R)
Recommended constants:
   Refractive index of cornea=1.336
   Retinal thickness factor=0
Measured and extrapolated values:
   K pre-LASIK= average K-reading before LASIK (D)
   K post-LASIK= estimated refractive corneal power after LASIK (D)
   AL=measured axial length (mm)
Chosen values
   V=vertex distance of pseudophakic spectacles (mm), default=12 mm
   pACD=personalized anterior chamber depth constant
   pACD=0.58357× A constant-63.896
Calculated variables
   P=power of the IOL (D)
   R=refractive error at corneal plane (D)
   Rx=target refractive error at spectacle plane (D)
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