Hong 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 outcomes Most commonly performed surgery Increased patient expectation  Adopt practices that promote the patient’s best interests and safety in performing cataract surgery

Possible complications in 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

Our pledge last year  Continuous audit for SA60AT IOL  To determine optimized A constant for SN60WF

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 years (range, 28-96)  Axial length mm (range, 21.1 – 29.94)  34 phaco surgeons

Refractive outcomes  Mean post-op spherical equivalent (SE) – D (range, to 2.0) Pearson correlation r = P = 0.735

Refractive outcomes Axial Length (mm) <22 22 – 26 >26 No. of eyes Difference in SE from target (D) (-2.42 to 0.7) (-3.01 to 2.5) (-3.22 to 3.71) One-way ANOVA: p=0.366

Comparison of outcomes  Mean target SE -0.67D (range, to 0.72)  Mean post-op SE D (range, to 2.0) p<  Mean difference between target and post-op SE: 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 ( 80 years old) p=0.798  Laterality of eyes p=0.733  Axial length ( 26mm) P=0.994

Factor analysis  Biometry machine performance Chi-square test p=0.017 Axis IICannonNidek 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

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 NursingOptometristOrthoptist 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

Discussion  Biometry performance significantly better for PAPD nursing staff Nidek machine  Majority of biometry service done by nursing staff using Nidek machine Most experienced  More difficult cases are diverted to orthoptist Account for lower accuracy May 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  SN60WF Aspheric Reduced 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

 Thank You