hong kong eye hospital ms frenchy chiu dr victoria wong iol master 20111
TRANSCRIPT
Hong Kong Eye HospitalHong Kong Eye Hospital
Ms Frenchy Chiu
Dr Victoria Wong
IOL master 2011 1
Introduction Accurate biometry is an essential component of
cataract surgery. Preoperative measurement of axial length is the
most critical factor for accurate calculation of the intraocular lens power.
A measurement error of 100μm results in a postoperative refractive error of 0.28D.
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Introduction Carl Zeiss IOLMaster 500 Advanced Technology V7.1
Optical coherence biometryUses infrared diode laser (λ 780 nm) of high spatial
coherence and short coherence length (160μm)Measures axial length between the corneal vertex and
retinal pigment epithelium along the visual axis using a red fixation beam, with a resolution of 12μm and precision of 5μm
Provides a non-contact technique with no risk of infection or corneal abrasion
Previous model available in HKEH till 2006
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Introduction Other modality of biometry
Ultrasound ○ Nidek Echoscan 1800 – most frequently used○ Quantel Medical Axis II○ Canon IOL Estimator KU-1 (until Jan 2011) –
combined Keratometry and A-scan
ApplanationMeasures anatomic length of the eyeMore user-dependant
A-constant for SN60WF
Nominal 118.7
On average the axial lengths measured by IOLMaster were longer by 0.15 mm compared to ultrasound biometry*
Optimized A-constants for IOLMaster using SRK/T formula is 119.0 or 119.1 (Japanese)#
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*Rose et al. CEO 2003#data by C.Suto, MD, Tokyo, Japan
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http://www.augenklinik.uni-wuerzburg.de/ulib/c1.htm
Purpose of audit To trial run the newly acquired Carl Zeiss IOL Master
500
To determine the accuracy of biometry by comparingthe expected spherical equivalent (SE) with the
achieved spherical equivalent (SE)with ultrasound biometry using Cannon IOL Estimator
KU-1
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Method and Patients Oct 2010 – Dec 2010 Single biometrist
Carl Zeiss IOLMaster (including IOLMaster keratometry module)
Cannon IOL Estimator KU-1 Single surgeon
Uneventful phacoemulsification + IOLTemporal phacoSN60WFRemoval of OVD from under the IOL at the end
of surgery
Results 19 eyes of 19 patients Female : Male 16 : 3 Left : Right 7 : 12 Age 77.3 years (range, 62 - 89) Mean axial length (IOLMaster) 21.97 mm (range,
21.38 to 25.74) Mean IOL power +22.0D (range, +15.0 to +28.5)
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Results
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Axis II IOLMaster P-value*
Average K (D)44.09
(41.12 to 45.75)44.14
(41.44 to 45.82)0.21
Axial Length (mm)23.22
(20.92 to 26.40)23.47
(21.38 to 25.74)0.007
Target SE (D)0.47
(1.83 to +0.21)0.79
(1.10 to 0.03)0.065
Achieved SE (D)0.42
(1.25 to +0.25)
Difference between target and achieved SE (D)
+0.37(0.96 to +1.26)
Within ± 1 D of target (%) 89
2-tailed t-test
Summary of findings The K values obtained with the IOLMaster keratometry
module and the manual Cannon KU-1 keratometer were found not to be significantly different.
The axial length data was normally distributed and found to be longer when measured with the IOLMaster. This difference was statistically significant. slightly different measurement paths and the additional distance
to the retinal pigment epithelium
The difference in target and achieved SE was +0.37D and 89% of patients were within 1D of target refraction.
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Plot of axial length measurements between the IOLMaster and A-scan ultrasound with a correlation coefficient of 0.97, P< 0.001.
Conclusion The IOLMaster provides accurate axial length and
keratometric measurements and determination of IOL power
The use of the optimized A-constant 119.1 (Japanese) results in accurate IOL prediction. Further optimization of A-constant for SN60WF IOL is not indicated at this stage
Continuous audit of other commonly used IOL should be considered
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Thank you