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

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 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

Thank You