Hong Kong Eye HospitalHong Kong Eye Hospital

Biometry Audit 2012

SN60WF IOL

Dr. Rose Chan

Resident, Hong Kong Eye Hospital

Acknowledgement

Pre-admission and post-discharge (PAPD) nursing staff

Medical Record Office (MRO) 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

Summary of last year result

Mean difference between target and post-op SE: -0.58 D (range, -3.22D to +3.7D)

Within ± 1 D of target SE 64.6 % (177/274)

Biometry performance significantly better forPAPD nursing staff Nidek machine

Suggestions from last year To concentrate biometry service by

experienced staff

To aim emmetropia for SN60WF Choose target refraction between 0D and -0.5D

To repeat audit next year To refine A-constant if similar outcome

Methods July 2010– Oct 2011 Patients implanted with SN60WF (15-20% of IOL in 2011)

Biometry by PAPD NS, optometrists and orthoptists SRK/T formula regardless of axial length Uneventful phacoemulsification + IOL Major reasons for exclusion

○ Combined surgeries○ No refraction available○ Complicated surgery

Methods

Data CollectedDemographicsAxial length, keratometryBiometry machine and staffTarget and outcome refraction

Biometry staff and machineNursing Optometrist Orthoptist

Nidek Echoscan

n= 196/390 (50.3%)● ● ○

Quantel Medical Axis

n= 110 (28.2%)● ●

Canon KU-1

n= 40 (10.3%)●

Alcon Ocuscan

n= 22 (5.6%)●

Zeiss IOL Master

n= 22 (5.6%)●

Current A-constant

For USG biometry: 118.7 For Optical biometry: 119.1

Results 897 SN60WF IOL were implanted

~15% total IOL

390 eyes were included into audit Female : Male 225:135 Left : Right 189:201 Age 74.4 years (range, 38-93 years) Axial length 23.64 mm (range, 20.0 –

30.28mm)

Refractive outcomes Mean post-op spherical equivalent (SE) –

-1.13 D (range, -7.25D to +3.125D)

Pearson correlation

r = -0.21

P = 0.735

Comparison of outcomes Mean target SE -0.61D (range, -4.66D to +0.44D) Mean post-op SE -1.13 D (range, -7.25D to +3.12D)

p<0.0001 (two-tailed t-test)

Mean difference between target and post-op SE: -0.52 D (-3.8D to +3.46D)

Calculation based on surgeon’s chosen target refraction

Within ± 1 D of target SE 64.9 % (253/390)

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 rangeChi-square test

Sex p=0.45

Age (<60, 60-80, >80 years old)p=0.83

Laterality of eyes p=0.733

Factor analysis

Axial Length (mm)Axial Length (mm) <22<22 22 – 2622 – 26 >26>26

No. of eyes No. of eyes 3434 325325 3131

Mean difference in SE Mean difference in SE from target (D)from target (D)

-0.86 (-1.58 -0.86 (-1.58 to 3.8)to 3.8)

-0.52 (-3.46 -0.52 (-3.46 to 2.87)to 2.87)

-0.14 (-1.76 to -0.14 (-1.76 to 2.59)2.59)

One-way ANOVA: p=0.012

Factor analysis Biometry machine performance

Nidek Axis Canon Ocuscan IOL Master

Wiithin +/- 1D target refraction

145 (74%)

53

(48%)

24

(60%)

14

(63.6%)

17

(77.3%)

Not within

target 51 57 16 8 5

Total 196 110 40 22 22

Chi square test p<0.0001

Factor analysis Biometry staff performance by group

Chi-square test p<0.0001

Nursing Optometrist Orthoptist

Within +/- 1D of target refraction

103 (77.4%) 86 (51.8%) 64 (64.9%)

Out of target refraction range

30 80 27

Total 133 166 91

Factor analysis

Machine performance? Staff performance?

Factor analysis Axis II

Used by Optometrist and Orthoptist

Optometrist Orthoptist

Within target 30 (38%) 23 (74.2%)

Not within target

49 8

Total 79 31

Chi-square test P<0.001

Factor analysis Excluding cases of Axis II machine

Nursing Optometrist Orthoptist

Within +/- 1D of target refraction

103 (77.4%) 56 (64.4%) 41 (68.3%)

Out of target refraction range

30 31 19

Total 133 87 60

Chi square test: p=0.091

Factor analysis

No significant difference of individual optometrist performance P=0.658 (Chi-square)

Discussion Suboptimal biometry outcomes not reaching 80% target

Overall biometry performance significantly better for PAPD nursing staff Nidek / IOL master machines

Previous years: most biometry performed by nursing staff But more biometry service to be taken up by optometrist

Need further enhancement of skills and technique

Discussion

Current biometry service allocation

Nursing Optometrist Orthoptist

No. of sessions per week

6 3 1

Patient share 40 % 40 % 20 %

Discussion Mean target refraction of our surgeons:

-0.61D SN60WF

AsphericReduced spherical aberration best when

emmetropic

Myopic shift significantly more in short AL eyesAim emmetropia especially for short eyeball

Discussion

Poor results from Axis II machineNo longer in use

Recommendations Further streamline biometry service is essential

Too many machines and groups of staff○ high variability

To concentrate biometry service by experienced staff

Machines in current use:

Nursing Optometrist Orthoptist

Nidek old model ●

Nidek new model ● ●

IOL Master ● ●

Optometrist service improvementAudit for individual performanceEstablish protocol for double check mechanismImprove setting for biometry measurement

○ Head support, fixation targetUse of IOL master

○ Less technique demanding

To aim emmetropia for SN60WF Choose target refraction between 0 and -0.5D

○ Especially for short eyes

Recommendations

Re-calculation of optimized A-constant (excluding cases by Axis-II and IOL master)

Using Dr Warren Hill Constant Calculation spreadsheet

Modified optimized A-constant 118.2

Recommendations

Current optimization not applicable to IOL master (optical biometry)To review in coming yearMore cases anticipated coming year

○ 2/3 cases of nursing (VA better than 3/24)

Thank You