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Quality Control in Refractive Surgery

Stefan Pieger*, M.Sc.

•Ingenieurbüro Pieger GmbH, Wendelstein, Germany

Introduction

Personal experience as application specialist for refractive excimer lasers since 1987. (Meditec, Schwind, Nidek)PRK & LASIK Nomogram development based on systematic outcomes analysis.Excimer Laser Surgery and refractive surgery in general well suited for a systematic approach on quality control.

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Why Quality Control?Verify current nomogram settings and make adjustments if necessary.Reduce enhancement rate.Use for marketing and advertisement.Discover trends and technical problems in order to react more rapidly.Fulfill requirements of ophthalmic societies. Increase confidence level about refractive procedures offered in your center.

How to collect your data?

Patients files

Excel Spread Sheet

Database Software (Access; Filemaker; etc.)

Outcomes Analysis Software (Datagraph; ASSORT; Refr. Consultant; etc.)

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How to analyze refractive data?Standard Refractive Outcomes (JRS)

Stability / Safety / Predictability / EfficacyAdditional Outcome Parameters

Astigmatism Outcomes: SIRC - Surgically Induced Refractive Change (=‘Vector Analysis’); Double Angle Scatter PlotDefocus Equivalent / Contrast Sensitivity in mesopic conditions / pre OP BSCVA vs. post OP UCVA

Wavefront Based OutcomesDefocus + Cyl (‘aberrometer refraction’)Higher Order RMS / Spherical Aberration (Z12) / Coma / Trefoil

Standard Outcomes

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www.slackinc.com/eye/jrs/vol164/war.pdf

Standard Refractive Outcomes: Safety

1% 0% 2% 0%

22%

13%

54%57%

19%25%

2% 3% 0% 0%0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

lost > 2 lost 2 lost 1 unchanged gained 1 gained 2 gained > 2

2. SAFETY: Change in BSCVA - Percent

1 (770)3 (653)

month (eyes)

Follow up time interval

Number of eyes per Follow up visit.

2 or more lines lost 3 % at 1 m post OP

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Standard Refractive Outcomes: Efficacy

4%6%

18%26%

46%40%

14%14%10%7% 3%4% 5%3%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

20/12 orbetter

20/15 20/20 20/25 20/30 20/40 20/50 orworse

4. EFFICACY: UCVA - Percent

1 m (691)3 m (562)

month (eyes)

Follow up time interval

Number of eyes per Follow up visit.

72% 20/20 or better 3 month post Op

8%

32%

90%

48%

95%

76%

95%

84%

100%

88%

100%

12%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Dat

agra

ph

'20/10

'

20/12

,5 or b

etter

20/16

or bett

er

20/20

or bett

er

20/25 o

r bett

er

20/32

or bett

er

20/40

or bett

er

20/50

or bett

er

20/63

or wor

se

preOP SCVA vs. postOP UCVA - Percentage

3 m (25)preSCVA (39)

month(eyes)

Standard Refractive Outcomes: Cumulative UCVA vs. preOP SCVA

PreOP SCVA

Number of eyes at Follow up visit.

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Standard Refractive Outcomes: Stability (SEQ)

1. STABILITY: Achieved Change in Refr. over Time

-0,22-0,18-0,20-0,15

-4,70

1189 744 662 42 25-8,00

-7,00

-6,00

-5,00

-4,00

-3,00

-2,00

-1,00

0,00

1,00

pre OP 1 m 3 m 6 m 12 m ± 1 StDev

Follow up time interval

Mean value of SEQ

Number of eyes per Follow up visit.

Standard Refractive Outcomes: Predictability (SEQ)

PREDICTABILITY: Attempted vs Achieved (Scatter) 744 eyes

y = -0.00x2 + 0.94x + 0.21

012345

6789

1011

12131415

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Attempted delta SR equiv. [D]Dat

agra

ph

Achieved [D]

overcorrected

undercorrected

Number of eyes at follow up

±1 D ‘happiness’ Zone

Trend line

y = -0.00x2 + 0.94x + 0.21Regression Formula: ‘Achieved = 0.94*Attempted’(~6% undercorrection)

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Astigmatism Outcomes:must be based on Vector Analysis!SIRC (Surgically Induced Refractive Change)

PreOP: -5/-2 x 180°

1 month: Plano/-1 x 130°

SIRC: -4.31/-2.39 x 12°

'The cylinder was actuallyovercorrectd and the axis has

been misaligned by 12°!'

Astigmatism Outcomes:SIA (based on Vector Analysis)

Attempted Cyl vs SIA (Scatter) 3 month postOP 490 eyes

y = -0.00x2 + 0.90x + 0.04

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6 7

Attempted Cyl [D]Dat

agra

ph

Achieved [D]

overcorrected

undercorrected

y = 0.90 * x(~10% undercorrection)

-2/-1@180°

0/-0.5 x 90°(-0.5/+0.5x180°)

0.5 D CylOvercorrection!

0/-0.5 x 180°

0.5 D CylUndercorrection!

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Astigmatism Outcomes:Double Angle Scatter Plot

Double Angle Minus Cyl Scatter Plot (160 eyes)

-5

-4

-3

-2

-1

-0

-1

-2

-3

-4

-5

-5 -4 -3 -2 -1 -0 -1 -2 -3 -4 -5

Mean Cyl -0,53 @ 6,9°

Datagraph

0°

45°

90°

135°

PreOP Cyl & Axis PostOP Cyl & AxisDouble Angle Minus Cyl Scatter Plot (79 eyes)

-5

-4

-3

-2

-1

-0

-1

-2

-3

-4

-5

-5 -4 -3 -2 -1 -0 -1 -2 -3 -4 -5

Mean Cyl -0,09 @ 162,3°

Datagraph

0°

45°

90°

135°

Additional Outcomes:Defocus Equivalent

60%64%

86%88%

99%99% 100%100% 100%100% 100%100%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

<=0,5D <=1D <=2D <=3D <=4D <=5D

DEFOCUS EQUIVALENT - Percent

1 m (615)3 m (554)

month (eyes)

SEQ =

SPH + ½ CYL

DEQ =

|SEQ|+|½ CYL|

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72%76%

92% 92%99% 99% 100%100%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

+- 0,5 +- 1,0 +- 2,0 +- 3,0

Refractive outcome - % within | Attempted | 1 m (744) 3 m (662)

Defocus Equivalent vs. Refractive Outcome

60%64%

86% 88%

99% 99% 100%100%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

<=0,5D <=1D <=2D <=3D

DEFOCUS EQUIVALENT - Percent

1 m (615)3 m (554)

-5.0/+10.0 x 90°SEQ PlanoDEQ +5

DEQ ~ ‚Blur Circle‘

Additional Outcomes:Mesopic Contrast Sensitivity

Contrast Sensitivity Mesopic

1,63

1,88

1,57

1,21

1,68

1,92

1,61

1,22

0,40

0,60

0,80

1,00

1,20

1,40

1,60

1,80

2,00

2,20

A (3cpd) B (6cpd) C (12cpd) D (18cpd)

pre op (112)1 m (72)

month (eyes)

Spatial Frequency [cycles/degree]

Normal Population Range (Vector Vision CSV 1000)

VA in LogMar Scale

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Wavefront based Outcomes

„Work in progress“ !Important parameters: HO RMS, spherical Aberration and ComaReport on same (6mm) pupil diameter or convert to dioptersPresenting horizontal and vertical Coma individually? Vector calculation to present magnitude and axis in [D]! (0.5 D Coma @ 230°)

Wavefront based Outcomes –Higher Order RMS [µm ±StDev]

RMS higher order over time

0,540,540,510,53

0,31

52 26 29 11 30,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

pre OP 1 m 3 m 6 m 9 m

Pupil Diameter: 6.0 mm

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Wavefront based Outcomes –Spherical Aberration [µm] or [D]

Spherical Aberration (Z12) over time [µm]

-0,24-0,25

-0,23

-0,03

18 13 11 6-0,40

-0,35

-0,30

-0,25

-0,20

-0,15

-0,10

-0,05

0,00

0,05

0,10

pre OP 1 m 3 m 9 m

Spherical Aberration (Z12) DEQ over time [D]

1,521,421,361,31

0,41

18 13 11 7 60,00

0,50

1,00

1,50

2,00

2,50

pre OP 1 m 3 m 6 m 9 m

Dat

agra

ph

Pupil Diameter: 6.0 mm

Coma as Vector- Scatter PlotComa Scatter Plot (18 eyes)

-2,5

-2,0

-1,5

-1,0

-0,5

-0,0

-0,5

-1,0

-1,5

-2,0

-2,5

-2,5 -2,0 -1,5 -1,0 -0,5 -0,0 -0,5 -1,0 -1,5 -2,0 -2,5

Coma [D] 0,12 @ 202,4°

Datagraph

0°

90°

180°

270°

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Making Outcome-based Nomogram Adjustments

Comparison of Laser Settings vs. Achievedchange in refraction (and not Attempted vs. Achieved).Reduce random errors as far as possible as nomograms can only compensate systematicerrors!Must be specific for major laser parameters like OZ, TZ, ablation profile type as well as for refraction types.

Nomograms for Individual Patient Groups

Data must be filtered on certain parameters:Refraction Type (Myp/MyoAsti/Hyp/HypAsti…)Surgery Type (PRK; LASIK; LASEK; Custom…)Optical Zone DiameterOthers (age, laser software version; humidity…)

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Nomogram Improvements –Laser Settings vs. Achieved

Laser Settings vs Achieved 1166 eyes

y = -0,01x2 + 1,22x - 0,08

0123456

789

10111213

1415

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Laser setting [D]Dat

agra

ph

Achieved [D]

overcorrected

undercorrected

y = -0,01x2 + 1,22x - 0,08

reduce attemptedSEQ by 22%!

Laser Settings vs Achieved 1166 eyes

y = -0,01x2 + 1,22x - 0,08

0123456

789

10111213

1415

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Laser setting [D]Dat

agra

ph

Achieved [D]

overcorrected

undercorrected

Identify and exclude outliers

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Laser Setting CYL vs. Surgical Induced change in Astigmatism

Laser Setting (cyl) vs SIA 1480 eyes

y = 0.03x2 + 0.60x + 0.26

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6 7

LaserSetCyl [D]

Dat

agra

ph

Achieved [D]

overcorrected

undercorrected

1. High Scatter! (further analysis necessary!)

2. 40 % systematic undercorrection

Nomograms: General Comments1. Reduce Scatter by Standardized Surgery and OR

Environment2. Exclude Outliers from Data Analysis3. Exclude Enhancements (separate nomogram)4. Choose appropriate follow up interval (≥ 3 m)5. Create Formula („-10%“) / Lookup Table or use

Nomogram Software

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SummaryImproving the results of refractive surgery procedures must be based on an individual quality control system.Nomograms can compensate for systematic errors, but not for random errors.Modern outcomes analysis software allows constant monitoring of your results.Conventional Outcomes will be extended by HO-RMS, Spherical Aberration and Coma.

Thank You!

www.datagraph-med.com

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