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Carol B Toris, Richard Helms, Eric Chan, Ganiru Anunike, Kshama Girish, Joshua Buzzard, Padmanabhan P Pattabiraman; Validation of changes in anterior chamber biometrics in rabbit eyes measured by ultrasound biomicroscopy. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2189.
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© ARVO (1962-2015); The Authors (2016-present)
This study demonstrates and validates changes in anterior chamber biometrics measured by ultrasound biomicroscopy (UBM) during two-minute pneumatonography.
Ten female Dutch-Belted rabbits were lightly sedated with ketamine and xylazine then placed in a lateral decubitus position. Tonography was performed for 2 minutes using a pneumatonometer with a 10 gram weight applied to the shaft of the tonometer probe and placed on the cornea of the right eye. Serial images of the anterior chamber (AC) from the nasal to temporal edges were captured with UBM before and after tonography. The procedures were repeated for the left eye. Five independent observers identified points on each image to assist algorithim-based measurements of the AC volume, AC depth, AC angles, and corneal radius of curvature using Mathematica software. Comparisons were made before and after tonography by two-tailed t-tests. Intraclass and interclass correlation coefficients were determined to assess intra and inter observer variability.
The AC volume was 221.43 ± 27.9 µL (mean±SD) before tonography and 213.77 ± 25.2 µL after tonography for a decrease in volume of 7.66 µL (p = 0.05). The interclass correlation coefficient across the five observers was 0.922. The mean intraclass correlation coefficient of single observers was 0.895 (range 0.789-0.933). The AC depth was 2.18 ± 0.16 mm before tonography and 2.08 ± 0.14 mm after tonography for a decrease in depth of 0.1 mm (p = 0.001). The AC angle was 28.46 ± 2.31 degrees before tonography and 26.93 ± 1.75 degrees after tonography for a decrease of 1.53 degrees (p = 0.003). The radius of curvature of the cornea did not change during tonography.
UBM is a potential tool for measuring real-time anterior chamber changes following external forces applied to the eye as in the case of tonography. The weighted probe on the cornea decreased the AC volume, depth and angle without causing significant corneal indentation. During the test, 3.83 µl/min drained from the anterior chamber, a value that can be used in the calculation of outflow facility. Additionally, this method is consistently repeatable with different observers. Future application will be directed to assist in outflow facility calculations in human subjects.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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