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.

IOL master 2011 2

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

IOL master 2011 3

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

IOL master 2011 6

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

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 + 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)

9IOL master 2011

Results

10IOL master 2011

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.

IOL master 2011 11

IOL master 2011 12

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