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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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