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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.
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Comparison of Automated and Manual Measurements of Horizontal Corneal Diameter in Contact LensWearers 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.
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 Orbscan Obs A Obs B
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 Observer A – Observer B 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. • 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.