Hong Kong Eye Hospital Ms Frenchy Chiu Dr Victoria Wong IOL master 20111

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. IOL master 20112

Introduction  Carl Zeiss IOLMaster 500 Advanced Technology V7.1 Optical coherence biometry Uses 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 IOL master 20113

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 Applanation Measures anatomic length of the eye More user-dependant

A-constant for SN60WF  Nominal  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 or (Japanese)# IOL master *Rose et al. CEO 2003 #data by C.Suto, MD, Tokyo, Japan

IOL master

Purpose of audit  To trial run the newly acquired Carl Zeiss IOL Master 500  To determine the accuracy of biometry by comparing the expected spherical equivalent (SE) with the achieved spherical equivalent (SE) with ultrasound biometry using Cannon IOL Estimator KU-1 7IOL master 2011

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 + IOL Temporal phaco SN60WF Removal 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, )  Mean axial length (IOLMaster) mm (range, to 25.74)  Mean IOL power +22.0D (range, to +28.5) 9IOL master 2011

Results 10IOL master 2011 Axis IIIOLMasterP-value* Average K (D) (41.12 to 45.75) (41.44 to 45.82) 0.21 Axial Length (mm) (20.92 to 26.40) (21.38 to 25.74) Target SE (D)  0.47 (  1.83 to +0.21)  0.79 (  1.10 to  0.03) Achieved SE (D)  0.42 (  1.25 to +0.25) Difference between target and achieved SE (D) (  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. IOL master

IOL master Plot of axial length measurements between the IOLMaster and A-scan ultrasound with a correlation coefficient of 0.97, P<

Conclusion  The IOLMaster provides accurate axial length and keratometric measurements and determination of IOL power  The use of the optimized A-constant (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 IOL master

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