title: Physical Factors Affecting Outflow Facility Measurements in Mice.
abstract: OBJECTIVE
  Mice are commonly used to study conventional outflow physiology. This study examined how physical factors (hydration, temperature, and anterior chamber [AC] deepening) influence ocular perfusion measurements in mice.
  
  
  METHODS
  Outflow facility (C) and pressure-independent outflow (Fu) were assessed by multilevel constant pressure perfusion of enucleated eyes from C57BL/6 mice. To examine the effect of hydration, seven eyes were perfused at room temperature, either immersed to the limbus in saline and covered with wet tissue paper or exposed to room air. Temperature effects were examined in 12 eyes immersed in saline at 20 °C or 35 °C. Anterior chamber deepening was examined in 10 eyes with the cannula tip placed in the anterior versus posterior chamber (PC). Posterior bowing of the iris (AC deepening) was visualized by three-dimensional histology in perfusion-fixed C57BL/6 eyes and by spectral-domain optical coherence tomography in living CD1 mice.
  
  
  RESULTS
  Exposure to room air did not significantly affect C, but led to a nonzero Fu that was significantly reduced upon immersion in saline. Increasing temperature from 20 °C to 35 °C increased C by 2.5-fold, more than could be explained by viscosity changes alone (1.4-fold). Perfusion via the AC, but not the PC, led to posterior iris bowing and increased outflow.
  
  
  CONCLUSIONS
  Insufficient hydration contributes to the appearance of pressure-independent outflow in enucleated mouse eyes. Despite the large lens, AC deepening may artifactually increase outflow in mice. Temperature-dependent metabolic processes appear to influence conventional outflow regulation. Physical factors should be carefully controlled in any outflow studies involving mice.
authors.affiliation: Department of Bioengineering Imperial College London, London, United Kingdom.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Boussommier-Calleja
authors.affiliation: Department of Ophthalmology, Duke University, Durham, North Carolina, United States.
authors.forename: Guorong
authors.initials: G
authors.lastname: Li
authors.affiliation: Department of Bioengineering Imperial College London, London, United Kingdom.
authors.forename: Amanda
authors.initials: A
authors.lastname: Wilson
authors.affiliation: Department of Bioengineering Imperial College London, London, United Kingdom.
authors.forename: Tal
authors.initials: T
authors.lastname: Ziskind
authors.affiliation: Department of Bioengineering Imperial College London, London, United Kingdom.
authors.forename: Oana Elena
authors.initials: OE
authors.lastname: Scinteie
authors.affiliation: Department of Ophthalmology, Duke University, Durham, North Carolina, United States.
authors.forename: Nicole E
authors.initials: NE
authors.lastname: Ashpole
authors.affiliation: Department of Bioengineering Imperial College London, London, United Kingdom.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Sherwood
authors.affiliation: Department of Ophthalmology, Duke University, Durham, North Carolina, United States.
authors.forename: Sina
authors.initials: S
authors.lastname: Farsiu
authors.affiliation: Department of Ophthalmology, Duke University, Durham, North Carolina, United States.
authors.forename: Pratap
authors.initials: P
authors.lastname: Challa
authors.affiliation: Department of Ophthalmology, Duke University, Durham, North Carolina, United States.
authors.forename: Pedro
authors.initials: P
authors.lastname: Gonzalez
authors.affiliation: Department of Ophthalmology, The University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States.
authors.forename: J Crawford
authors.initials: JC
authors.lastname: Downs
authors.affiliation: Department of Bioengineering Imperial College London, London, United Kingdom 4Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, United States.
authors.forename: C Ross
authors.initials: CR
authors.lastname: Ethier
authors.affiliation: Department of Ophthalmology, Duke University, Durham, North Carolina, United States.
authors.forename: W Daniel
authors.initials: WD
authors.lastname: Stamer
authors.affiliation: Department of Bioengineering Imperial College London, London, United Kingdom.
authors.forename: Darryl R
authors.initials: DR
authors.lastname: Overby
mesh_terms: D000818:Animals; D000867:Anterior Chamber / Q000166:cytology / Q000378:metabolism*; D001082:Aqueous Humor / Q000378:metabolism; D015353:Eye Enucleation; D005260:Female; D021621:Imaging, Three-Dimensional; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D041623:Tomography, Optical Coherence; D014129:Trabecular Meshwork / Q000378:metabolism*