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Eric Chan, Ganiru Anunike, Richard Helms, Padmanabhan P Pattabiraman, MARYO KOHEN, Ishita Gupta, Carol B Toris; Effect of Pneumatonography on Anterior Chamber Biometrics in Rabbit Eyes. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2694.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate changes in anterior chamber (AC) biometrics after two-minute tonography using ultrasound biomicroscopy (UBM) and to correlate the structural changes with intraocular pressure (IOP) in normal rabbit eyes
Ten female Dutch-Belted rabbits were lightly sedated with ketamine and xylazine then placed in a lateral decubitus position. Tonography was performed using a pneumatonometer with a 10 gram weight applied to the shaft of the tonometer probe and placed on the cornea for 2 minutes. IOP was measured with a pneumatonometer at baseline, during tonography measurement, and after tonography was completed. Serial images of the complete AC from the nasal to temporal edges were captured with UBM before tonography and immediately after, 5 minutes after and 10 minutes after tonography. AC depth, volume, and angles were measured using ImageJ and Mathematica software.
The AC volume decreased immediately after removing the probe from the cornea at the end of the tonography procedure, a decrease from 208.40±36.3 (mean±SD) to 198.53±39.9 uL (p=0.02). Anterior chamber depth did not change compared to baseline: 2.44±0.22 to 2.46±0.11 um (p=0.86). The IOP decreased from 36.1±5.6 at the start of tonography to 28.7±7.2 mmHg (p=0.004) at the end of tonography. The AC angle did not change immediately after tonography compared to baseline: 31.2±4.2° to 30.9±5.3° (p=0.72). However, the AC angle compared to baseline increased to 33.1±5.9° (p=0.009) and 36.0±7.2° (p=0.0001) at 5 and 10 minutes respectively. Just prior to application of the weighted probe, IOP was 22.9± 3.6 and after removing the probe, the IOP decreased to 21.7±3.1 mmHg (p=0.05). IOP then increased to 25.5±3.8 mmHg (p=0.02) and 25.6±2.2 mmHg (p=0.015) at 5 and 10 minutes respectively. A positive correlation (R =0.71) between AC angle and IOP was seen 10 minutes post-tonography. The mean outflow facility was 0.15±0.10 uL/min/mm Hg. No significant correlation was noted between AC angle and outflow facility.
Tonography caused significant changes in the shape of the anterior chamber over time as noted on UBM under physiological conditions. These changes correlated to changes in IOP and demonstrate a rebound effect over time in a normal eye. We believe that these homeostatic mechanisms may fail in glaucomatous eyes due to altered tissue elasticity which manifests as dynamic anterior chamber biometrics.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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