Aqueous Humor Dynamics of the Brown-Norway Rat

Abstract

PurposeThe study aimed to provide a quantitative description of aqueous humor dynamics in healthy rat eyes.MethodsOne eye of 26 anesthetized adult Brown-Norway rats was cannulated with a needle connected to a perfusion pump and pressure transducer. Pressure-flow data were measured in live and dead eyes by varying pump rate (constant-flow technique) or by modulating pump duty cycle to hold intraocular pressure (IOP) at set levels (modified constant-pressure technique). Data were fit by the Goldmann equation to estimate conventional outflow facility (\begin{document}\newcommand{\bialpha}{\boldsymbol{\alpha}}\newcommand{\bibeta}{\boldsymbol{\beta}}\newcommand{\bigamma}{\boldsymbol{\gamma}}\newcommand{\bidelta}{\boldsymbol{\delta}}\newcommand{\bivarepsilon}{\boldsymbol{\varepsilon}}\newcommand{\bizeta}{\boldsymbol{\zeta}}\newcommand{\bieta}{\boldsymbol{\eta}}\newcommand{\bitheta}{\boldsymbol{\theta}}\newcommand{\biiota}{\boldsymbol{\iota}}\newcommand{\bikappa}{\boldsymbol{\kappa}}\newcommand{\bilambda}{\boldsymbol{\lambda}}\newcommand{\bimu}{\boldsymbol{\mu}}\newcommand{\binu}{\boldsymbol{\nu}}\newcommand{\bixi}{\boldsymbol{\xi}}\newcommand{\biomicron}{\boldsymbol{\micron}}\newcommand{\bipi}{\boldsymbol{\pi}}\newcommand{\birho}{\boldsymbol{\rho}}\newcommand{\bisigma}{\boldsymbol{\sigma}}\newcommand{\bitau}{\boldsymbol{\tau}}\newcommand{\biupsilon}{\boldsymbol{\upsilon}}\newcommand{\biphi}{\boldsymbol{\phi}}\newcommand{\bichi}{\boldsymbol{\chi}}\newcommand{\bipsi}{\boldsymbol{\psi}}\newcommand{\biomega}{\boldsymbol{\omega}}C\end{document}) and unconventional outflow rate (\begin{document}\newcommand{\bialpha}{\boldsymbol{\alpha}}\newcommand{\bibeta}{\boldsymbol{\beta}}\newcommand{\bigamma}{\boldsymbol{\gamma}}\newcommand{\bidelta}{\boldsymbol{\delta}}\newcommand{\bivarepsilon}{\boldsymbol{\varepsilon}}\newcommand{\bizeta}{\boldsymbol{\zeta}}\newcommand{\bieta}{\boldsymbol{\eta}}\newcommand{\bitheta}{\boldsymbol{\theta}}\newcommand{\biiota}{\boldsymbol{\iota}}\newcommand{\bikappa}{\boldsymbol{\kappa}}\newcommand{\bilambda}{\boldsymbol{\lambda}}\newcommand{\bimu}{\boldsymbol{\mu}}\newcommand{\binu}{\boldsymbol{\nu}}\newcommand{\bixi}{\boldsymbol{\xi}}\newcommand{\biomicron}{\boldsymbol{\micron}}\newcommand{\bipi}{\boldsymbol{\pi}}\newcommand{\birho}{\boldsymbol{\rho}}\newcommand{\bisigma}{\boldsymbol{\sigma}}\newcommand{\bitau}{\boldsymbol{\tau}}\newcommand{\biupsilon}{\boldsymbol{\upsilon}}\newcommand{\biphi}{\boldsymbol{\phi}}\newcommand{\bichi}{\boldsymbol{\chi}}\newcommand{\bipsi}{\boldsymbol{\psi}}\newcommand{\biomega}{\boldsymbol{\omega}}{F_{un}}\end{document}). Parameter estimates were respectively checked by inserting a shunt of similar conductance into the eye and by varying eye hydration methodology.ResultsRat IOP averaged 14.6 ± 1.9 mm Hg at rest. Pressure-flow data were repeatable and indistinguishable for the two perfusion techniques, yielding \begin{document}\newcommand{\bialpha}{\boldsymbol{\alpha}}\newcommand{\bibeta}{\boldsymbol{\beta}}\newcommand{\bigamma}{\boldsymbol{\gamma}}\newcommand{\bidelta}{\bol...

Intracranial pressure modulates aqueous humour dynamics of the eye

“…C was 22 ± 4 nl/min/mmHg at resting ICP, which is indistinguishable ( p = 0.68) from reported values in rats not subjected to cerebral ventricle cannulation (Ficarrotta et al . ). C was 13 ± 3 nl/min/mmHg at high ICP, a reduction of 41.0 ± 13.4% ( p < 0.01).…”

“…The conventional outflow facility ( C ), or hydraulic conductance, of the eye was measured using a modified constant‐pressure perfusion technique (Ficarrotta et al . ), in which a control algorithm switched the pump on and off to maintain IOP within 2 mmHg of a user‐specified level. Net outflow ( F ) was calculated for different IOP set points as the product of pump duty cycle ( D ) and pump flow rate ( Fp ).…”

“…Pupils of both eyes were dilatated with 1% cyclopentolate hydrochloride drops to normalize pupil size and block pupillary changes. The anterior chamber of one eye was cannulated with a 33G needle connected via a three-way stopcock and tubing (length: 45 cm, lumen width: 0.4 mm) to a pressor sensor and a programmable syringe pump (NE-1000, New Era Pump Systems, Farmingdale, NY, USA) filled with artificial aqueous humour (Ficarrotta et al 2018). Corneas were kept moist by covering with clear contact lenses (OcuScience, Henderson, NV, USA) and instilling every 10-15 min with saline drops.…”

“…The calibration procedure has been described and the hydrodynamic properties of the eye perfusion system (e.g. needle resistance, tubing compliance) have been reported and were found to have negligible influence on outflow measurements (Ficarrotta et al 2018). Pressure sensor outputs were amplified, low-pass filtered at 1 Hz and digitized at 2 Hz by a custom LabView (National Instruments, Austin, TX, USA) computer program.…”

Experimental glaucoma model with controllable intraocular pressure history

“…Sensor output was calibrated against a mercury manometer prior to study commencement and verified intermittently thereafter. The calibration procedure and hydrodynamic properties of the system have been described 56 . There is a pressure drop between the sensor and the eye due to the cannula.…”