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

2. Financial disclosure
The authors have no financial interest in this study or presentation

3. 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.

4. 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.

5. Orbscan WTW

6. WTW WITH EYEMETRICS
5 point corneal reflections through which WTW is measured

7. 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 months).
All of them were using soft contact lenses

8. Results MEAN RANGE S.D CONFIDENCE INTERVAL ORBSCAN Automated 11.74
0.32
OBSERVER A
Manual
12.03
0.33
OBSERVER B
11.92

9. Results
Orbscan
Obs A
Obs B

10. 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

11. Results
Correlation R (p>0.05). Slope (P>0.05). Intercept (P =0.05).

12. Results
Observer A – Observer B
Average of measurements of Observer A & B
Correlation R (p>0.05). Slope (P>0.05). Intercept (P =0.05).

13. 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.

14. 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.
Manual corneal measurement can be very useful in patients with pannus and other peripheral corneal changes.
This method will be very useful adjuvant to automated measurement of corneal diameter in selection of Phakic intraocular lenses ( ICLs) and ACIOLs.

15. Thank you