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Chester C. Calvert, Lisa A Hethcox, Christopher A Girkin, J Crawford C Downs; Magnitude of Hypotony and Recovery Time Following Anterior Chamber Cannulation. Invest. Ophthalmol. Vis. Sci. 2014;55(13):118.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the magnitude of ocular hypotony and the length of recovery time following anterior chamber (AC) cannulation.
We have developed and validated an implantable telemetry system that wirelessly records 500 measurements of IOP per second for up to 2-1/2 years (IOVS 52(10):7365-75). Using an enhanced version of this system, continuous bilateral IOP, bilateral electro-oculogram (EOG), and aortic blood pressure were recorded both before and after anterior chamber cannulation with a 27G needle in two different sessions, 2 weeks apart in 3 young adult male rhesus macaques (NHP) aged 3-6 years old. Bilateral IOPs were recorded continuously while the NHPs were awake and behaving, under general anesthesia during IOP transducer calibration experiments involving manometric control of IOP via AC cannulation, then continuously after the AC needles were removed until IOP recovered to baseline levels. Bilateral IOP was quantified immediately after AC needle removal, and then the time to recovery to 6 mmHg and 10 mmHg was quantified.
Baseline IOP prior to anesthetic induction was 11.2 mmHg overall, and fell to 2.9 mmHg after AC needle removal (range 1.1 - 4.6 mmHg). On average, IOP took 53 minutes (range 21 - 88 min) and 83 minutes (range 57 - 94 min) to recover to 6 and 10 mmHg, respectively.
AC cannulation is common in animal studies and human patient procedures, but its lasting effects on IOP are unknown. Results show that the IOP falls to very low levels after AC needle removal, and the eye stays hypotonous for approximately an hour after needle removal. This should be taken into account when consideration of IOP or its effects is important.
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