Transcript INTRA-OCULAR LENS POWER CALCULATION IN POST …

INTRA-OCULAR LENS POWER
CALCULATION IN POSTREFRACTIVE SURGERY ASIAN
EYES USING THE HAIGIS-L
FORMULA
Dr Daphne Han, FRCS
Dr Wei-Han Chua, FRCS
Dr Peter Tseng, FRCS
The authors have no financial interest in the
subject matter of this presentation
Introduction
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Cataract surgery post-refractive surgery is noted for inaccuracies in
biometry arising from:
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radius error (curvature measurement)
keratometer index error (keratometric index)
intraocular lens (IOL) formula error (erroneous IOL positions)
Many strategies had been adopted to improve the accuracy of biometry
measurement, with varying degrees of ease of use1-5.
This study aims to report the results of IOL power calculation in
cataract surgeries after refractive surgery for myopia using the HaigisL formula, in Asian eyes.
✴ The Haigis formula developed by W. Haigis does not use corneal power as a
predictor for post-operative effective IOL position6, hence reducing the risk of
formula error.
✴ Haigis-L formula has been in use for about 4 years7, and is based on the
Haigis formula, with adjustment made for the post-myopic refractive surgery
corneal radius8 (derived from IOLMaster measurement), according to the
formula rcorr = 331.5 / (-5.1625 x rmeas) + 82.2603 - 0.35, where rcorr is the
corrected corneal radius of curvature and rmeas is the measured corneal radius
of curvature.
Methods
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Retrospective case series of all post-refractive surgery cataract
operations at the Singapore National Eye Centre from July 2008 to
September 2009.
33 consecutive cases of phacoemulsification and IOL implantation
post-refractive surgery for myopia were performed.
Post-operative refraction were done, at day 1
with the auto-refractor, and subsequently with
manifest refraction.
IOLMaster(V5, Carl Zeiss) biometry data and
post-op refraction results were analysed using
the SPSS (version 15.0.1) software.
Parameters
analyzed
•Mean axial length
•Mean anterior chamber depth
•Mean of measured corneal radii
•Mean arithmetic refractive error (ME)= post-op manifest
refraction – predicted refraction
•Mean absolute refractive error (MA)= absolute value of MA
•Median absolute refractive error
Results
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Haigis-L formula was used in 31 cases and post-operative
refraction available for 28 cases, which were analyzed.
Mean axial length was 27.61±1.95mm (range 23.88 to 32.53mm).
Mean anterior chamber depth was 3.42 ±0.29mm (range 2.80 to
3.97mm).
Mean of measured corneal radii was 8.85 ±0.52mm (range 7.66 to
9.93mm)
Average age of patient was 49.8 years (range 29 to 67 years).
All patients were of Asian racial background.
Two of the 28 cases analyzed were PRK and the rest were LASIK.
All cases were performed for myopia correction.
Our post-op refraction was done at a mean of 25.8 days (range 1
to 144 days).
Results
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Cataract surgeries were performed by a total of 14 surgeons;
Mean number of cases performed per surgeon was 2.28, ranging
from 1 to 7 cases per surgeon.
7 IOL types were used.
Types of IOL used
Lens type
MA60BM
SA60AT
SN60T5
SN60WF
SN6AD1
ZA9003
ZCB00
No. of
cases
2
12
1
12
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2
1
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Results
Mean absolute refractive error (MA) was
+0.81±0.51D (range +0.01 to +2.28D).
Median absolute refractive error +0.72D
Mean arithmetic refractive error (ME) was
-0.57 ±0.78D (range -2.28 to +1.25D).
Percentages of correct refraction predictions
Correct
refraction
prediction
±2.00D
±1.00D
±0.50D
Percentages
96%
75%
32%
Results in comparison to Haigis’s published
data (JCRS 2008; 34:1658-1663)
Parameters
Mean arithmetic
refractive error (ME)
Mean absolute refractive
error (MA)
Median absolute
refractive error
SNEC
-0.57±0.78D (range -2.28 +0.81±0.51D (range +0.01
to +1.25D)
to +2.28D)
+0.72D
HAIGIS
-0.04±0.70D (range -2.30 +0.51±0.48D (range +0.01
to +2.40D)
to +2.40D)
+0.37D
Correct refraction
prediction
±2.00D
±1.00D
±0.50D
SNEC
Percentages
(n= 28)
96%
75%
32%
HAIGIS Percentages
(n=187)
98.4%
84%
61.0%
Discussions
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Refractive results of IOL implantation after refractive surgery
are notorious for their marked variability in comparison to
eyes with virgin corneas6,9, due primarily to inaccurate
corneal radius measurement, and its effect on estimation of
the effective lens position. As refractive surgery becomes
more common, various methods had been suggested to
improve the predictability of biometry outcomes, using
nomogram adjustments, regression equations and IOL
formula modifications.
The clinical history method has been proposed as being the
most reliable method of calculating the net corneal power1012, but requires corneal measurements before refractive
surgery and treatment data, which may be absent.
Nevertheless, studies had found variation of biometry
results based on different formulae, using the clinical history
method13, with reports of mean absolute error ranging from
1.32±0.73D using the SRK-T formula13 to 0.75±0.52D using
the Hoffer Q formula.
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Discussion
Our study is limited by its small sample size and the
variable length of follow-up. Majority of the refractive
surgeries were performed elsewhere. However, all
phacoemulsifications were performed at our centre, by a
total of 14 surgeons, using a total of 7 lens types. We did
not encounter any dense or white cataracts that the
IOLMaster could not be applied upon.
Although the outcome shown in our study seem less
accurate in comparison to Haigis’s own report8, this may be
a result of the above limitations. The range of our outcome
is nevertheless similar to Haigis’s results. The span of our
ME was 3.53D and of the MA was 2.27D, compared to
Haigis’s 4.7D and 2.39 respectively, which show that our
results have a tighter spread.
Our outcome of the Haigis-L formula for IOL calculation of
post-refractive surgery Asian eyes compare reasonably well
with other formulae13. The Haigis-L formula has the
advantage of being extremely user-friendly since no clinical
history is required. The fact that in this study a total of 14
surgeons contributed to the results also attest to its
reliability and ease of use.
Summary
• Haigis-L requires no pre-refractive
surgery keratometry and treatment data
• Excellent ease of use compared to
other formulae, no extra calculations
required.
• Requires the IOLMaster.
• Not for white or dense posterior
subcapsular cataracts.
• Our results in Asian eyes with a diverse
number of surgeons and lens types
show its applicability.
References
1.Shammas HJ, Shammas MC. No-history method of intraocular lens power calculation for cataract surgery after
myopic laser in situ keratomileusis. J Cataract Refract Surg. 2007 Jan;33(1):31-6.
2.Borasio E, Stevens J, Smith GT. Estimation of true corneal power after keratorefractive surgery in eyes
requiring cataract surgery: BESSt formula. J Cataract Refract Surg. 2006 Dec;32(12):2004-14.
3.Rosa N, Capasso L, Romano A. A new method of calculating intraocular lens power after photorefractive
keratectomy. J Refract Surg. 2002 Nov-Dec;18(6):720-4.
4.Aramberri J. Intraocular lens power calculation after corneal refractive surgery: double-K method. J Cataract
Refract Surg. 2003 Nov;29(11):2063-8.
5.Koch DD, Wang L. Calculating IOL power in eyes that have had refractive surgery. J Cataract Refract Surg.
2003 Nov;29(11):2039-42.
6.Haigis W, Lege B, Miller N, Schneider B. Comparison of immersion ultrasound biometry and partial coherence
interferometry for intraocular lens calculation according to Haigis. Graefes Arch Clin Exp Ophthalmol. 2000
Sep;238(9):765-73.
7.Haigis W.[Preoperative intraocular lens power calculations in problem eyes]. Z Med Phys. 2007;17(1):45-54.
German.
8.Haigis W. Intraocular lens calculation after refractive surgery for myopia: Haigis-L formula. J Cataract Refract
Surg. 2008 Oct;34(10):1658-63.
9.Elder MJ. Predicting the refractive outcome after cataract surgery: the comparison of different IOLs and SRKII v SRK-T. Br J Ophthalmol. 2002 Jun;86(6):620-2
10. Savini G, Barboni P, Zanini M. Ophthalmology. 2006 Aug;113(8):1271-82. Intraocular lens power calculation
after myopic refractive surgery: theoretical comparison of different methods.
11. Morris AH, Whittaker KW, Morris RJ, Corbett MC. Errors in intraocular lens power calculation after
photorefractive keratectomy. Eye (Lond). 1998;12 ( Pt 2):327-8.
12. Kalski RS, Danjoux JP, Fraenkel GE, Lawless MA, Rogers C. J Refract Surg. Intraocular lens power
calculation for cataract surgery after photorefractive keratectomy for high myopia. 1997 Jul-Aug 13(4):362-6.
13. Fam HB, Lim KL A comparative analysis of intraocular lens power calculation methods after myopic excimer
laser surgery. J Refract Surg. 2008 Apr;24(4):355-60.
Corresponding author:
[email protected]
Thank you