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Hong Kong Eye HospitalHong Kong Eye Hospital
Biometry Audit 2011
SN60WF IOL
Dr. Rose Chan
Resident, Hong Kong Eye Hospital
Acknowledgement
Pre-admission and post-discharge (PAPD) nursing staff
Ms Chiu Wai Yee Dr. Victoria Wong
Introduction Importance of auditing cataract
surgery outcomesMost commonly performed surgery Increased patient expectation
Adopt practices that promote the patient’s best interests and safety in performing cataract surgery
Refractive surprise
Diminished quality of life Binocular diplopia Altered depth perception Lens exchange Medicolegal implications
Purpose of audit Royal College of Ophthalmologists Cataract
Surgery Guidelines 2010“The accuracy of the biometry should be
continuously audited by comparing the expected spherical equivalent with the achieved spherical equivalent.”
Refraction within 1 diopter of target is considered to be satisfactory
A benchmark standard of 85% is suggested
Methods Aug 2008 – July 2010 Patients implanted with SN60WF
Biometry by PAPD NS, optometrists and orthoptists Machines used:
Nidek Echoscan US-1800 (Nursing staff)○ 142/274 (51.82%)
Cannon KU-1 (Orthoptist)○ 63/274 (22.99%)
Quantel Medical Axis II (Optometrist/orthopist)○ 69 (25.18%)
SRK/T formula regardless of axial length
Uneventful phacoemulsification + IOL Major reasons for exclusion
○ Combined surgeries○ No refraction available○ Complicated surgery
Results 528 patients had SN60WF implanted 274 eyes of 265 patients were included into
audit Female : Male 149:116 Left : Right 125:149 Age 74.32 years (range, 28-96) Axial length 23.65 mm (range, 21.1 –
29.94) 34 phaco surgeons
Refractive outcomes Mean post-op spherical equivalent (SE) –
-1.25 D (range, -6.12 to 2.0)
Pearson correlation
r = -0.21
P = 0.735
Refractive outcomes
Axial Length (mm)Axial Length (mm) <22<22 22 – 2622 – 26 >26>26
No. of eyes No. of eyes 1515 236236 2323
Difference in SE from Difference in SE from target (D)target (D)
-0.79 (-2.42 -0.79 (-2.42 to 0.7)to 0.7)
-0.58 (-3.01 to -0.58 (-3.01 to 2.5)2.5)
-0.36 (-3.22 to -0.36 (-3.22 to 3.71)3.71)
One-way ANOVA: p=0.366
Comparison of outcomes Mean target SE -0.67D (range, -5.58 to 0.72) Mean post-op SE -1.25 D (range, -6.12 to 2.0)
p<0.0001
Mean difference between target and post-op SE: -0.58 D (-3.22 to 3.7)
Calculation based on surgeon’s chosen target refraction
Within ± 1 D of target SE 64.6 % (177/274)
Factor analysis SRK/T formula used in all patients Calculation based on surgeon’s chosen target refraction
Comparing proportion of patients within target refraction range (+/- 1D of target), and those not within target range Chi-square test
Sex p=0.744
Age (<60, 60-80, >80 years old) p=0.798
Laterality of eyes p=0.733
Axial length (<22, 22-26, >26mm) P=0.994
Factor analysis Biometry machine performance
Chi-square test p=0.017
Axis II Cannon Nidek
Within +/- 1D of target refraction
43 (62.3%) 33 (52.4%) 103 (72.5%)
Not within target refraction range
26 (37.7%) 30 (47.6%) 39 (27.5%)
Total 69 63 142
Factor analysis
Nidek machine performed better?true machine difference?related to operating staff performance
Limited by relative small number of cases done by Axis/Cannon machine
Factor analysis Biometry staff performance by group
Chi-square test p=0.002
Nursing Optometrist Orthoptist
Within +/- 1D of target refraction
97 (72.4%) 50 (68.5%) 32 (47.8%)
Out of target refraction range
37 (27.6%) 23 (31.5%) 35 (52.2%)
Total 134 73 67
Discussion Biometry performance significantly better for
PAPD nursing staff Nidek machine
Majority of biometry service done by nursing staff using Nidek machineMost experienced
More difficult cases are diverted to orthoptistAccount for lower accuracyMay improve with availability of IOL Master
Discussion
Re-calculation of optimized A-constant
Using Dr Warren Hill Constant Calculation spreadsheet
Modified optimized A-constant 118.5
Discussion
Mean target refraction of our surgeons: -0.67D
SN60WFAsphericReduced spherical aberration best when
emmetropic
Surgeons are suggested to aim near emmetropic while using SN60WF
Recommendations To concentrate biometry service by
experienced staff
To aim emmetropia for SN60WF Choose target refraction between 0 and -0.5D
To repeat audit next year To refine A-constant if similar outcome