Transcript Slide 1

Comparison of Automated and Manual
Measurements of Horizontal Corneal
Diameter in Contact Lens
Wearers Using Orbscan Eye Metrics
Function and Orbscan 11z Corneal
Topographer
Dr Venkataraman Arvind MD , MRCOphth.
M.Krithiga B.S.(Optom)
Vasan Eye Care Hospital,
Chennai, India
Financial disclosure
The authors have no financial interest in
this study or presentation
AIM
Comparison of automated and manual
measurements of horizontal corneal diameter
in contact lens wearers using Orbscan Eye
Metrics Function and Orbscan 11z corneal
topographer.
METHODS
Automated White to White (WTW)
measurement was obtained from the Orbscan II.
Using the Eye metrics function the WTW was
measured manually by two observers along the
five point corneal reflections on the Orbscan real
image.
The data was analysed using Statistica software
for correlation ,reliability and Inter-rater
repeatability.
Orbscan WTW
WTW WITH EYEMETRICS
5 point corneal reflections through which WTW is measured
Results
73 eyes of 37 patients were included in the
study.
25 females and 12 males.
Average duration of contact lens usage
was 34 months (range 16-52 months).
All of them were using soft contact lenses
Results
MEAN
RANGE
S.D
CONFIDENCE
INTERVAL
ORBSCAN
Automated
11.74
10.7-12.35
0.32
11.66-11.81
OBSERVER A
Manual
12.03
10.96-12.60
0.33
11.95-12.11
OBSERVER B
Manual
11.92
10.90-12.50
0.33
11.84-11.99
Results
Box & Whisker Plot
Box & Whisker Plot
Orbscan vs Eyemetrics measurementVar6
( Observer
A & B)
vs. Var14
16
16
15
15
14
14
13
13
12
12
11
11
10
10
Mean
Mean±SE
Mean±1.96*SE
Var6
Var9
Var6
Orbscan
Obs A
Var14
Obs B
Mean
Mean±SE
Mean±1.96*SE
RESULTS
Manual measurements (Observer A&B)
using eye metrics was statistically different
compared to the automated
measurements of Orbscan (p<0.001).
Standard deviation difference
Orbscan Vs OB-A is 0.19
Orbscan Vs OB-B is 0.10
Results
Correlation R 0.0009(p>0.05). Slope -0.008 (P>0.05). Intercept -0.079 (P =0.05).
Results
Bland Altman Plot Manual Measurement Obs A vs B
Diff
0.60
Linear (Diff)
0.50
Observer A – Observer B
0.40
0.30
0.20
0.10
y = -0.0336x + 0.4682
R2 = 0.0043
0.00
10.8
11
11.2
11.4
11.6
11.8
12
12.2
12.4
12.6
-0.10
-0.20
-0.30
-0.40
Average of measurements of Observer A & B
Correlation R 0.0043(p>0.05). Slope -0.0336 (P>0.05). Intercept 0.468 (P =0.05).
Results
Horizontal corneal diameter by manual
Eye metrics measurements are longer
than Orbscan derived measurements.
Manual measurement shows higher
inter-rater variability and test – retest
variability.
Variations tend to decrease with repeat
measurements.
Conclusion
Orbscan IIz corneal topographer underestimates the
WTW especially in long term contact lens wearers. This
error can be reduced by manual measurements using
Eye metrics software.
2) Manual corneal measurement can be very useful in
patients with pannus and other peripheral corneal
changes.
3) This method will be very useful adjuvant to automated
measurement of corneal diameter in selection of Phakic
intraocular lenses ( ICLs) and ACIOLs.
1)
Thank you