May 2005
Volume 46, Issue 13
ARVO Annual Meeting Abstract  |   May 2005
Computerized Water Column Perfusion– Simulated Outflow Facility Measurements
Author Affiliations & Notes
  • L. Camras
    Ophthalmology, Univ Nebraska Med Ctr, Omaha, NE
  • C. Toris
    Ophthalmology, Univ Nebraska Med Ctr, Omaha, NE
  • J. Berg
    Ophthalmology, Univ Nebraska Med Ctr, Omaha, NE
  • D. Eisenberg
    Ophthalmology, The Shepherd Eye Center, Las Vegas, NV
  • Footnotes
    Commercial Relationships  L. Camras, None; C. Toris, None; J. Berg, None; D. Eisenberg, None.
  • Footnotes
    Support  RPB
Investigative Ophthalmology & Visual Science May 2005, Vol.46, 3672. doi:
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    • Get Citation

      L. Camras, C. Toris, J. Berg, D. Eisenberg; Computerized Water Column Perfusion– Simulated Outflow Facility Measurements . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3672.

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      © ARVO (1962-2015); The Authors (2016-present)

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To evaluate the sensitivity and reproducibility of an Automated System (ARVO '01) to measure trabecular outflow facility.


A stepping motor pump, controlled by a computer, was used to fill and adjust the height of a 4mm diameter water column. The column was connected to a pressure transducer and then to a micro–pore filter, serving as the resistive element in the system. The outflow of fluid resulted in decreased fluid height in the column. At 15 second intervals while the fluid was flowing through the filter, pressure was monitored by the Automated System. Fluid was weighed on a microbalance and weights recorded by hand (Mass Measurement). The Automated System calculated several calibration slopes of pressure (mmHg) verses volume (uL) for the water column. An average of these calibrations was found to be 177.6 µl/mmHg. This value was used to convert pressure/time data into volume/time (flow) data. An outflow facility curve was generated over 3 different pressure heads (8, 16, 32 mmHg).


The table provides a summary of the results. The two methods to determine outflow facility correlated well with only a 10% margin of error. Facilities from the Automated System had a smaller standard deviation (0.0062 uL/min/mmHg) than from the Mass Measurement method (0.0236 uL/min/mmHg). At 32 mmHg perfusion pressure, both methods produced same facility values. At the 8 mmHg perfusion pressure, the Mass Measurement facility deviated more than the 10% margin of error and was 0.06 uL/min/mmHg less than the Automated System facility.



The deviation from the 10% margin of error at the lowest pressure (8 mmHg) of the Mass Measurement Method can be explained by noise from external factors that are significant at the very low flow rates. This was not a problem with the Automated System. Measuring outflow facility by the Automated System provides precise and reproducible data. It features ease of use, simple construction and reliable performance.


Keywords: intraocular pressure • clinical research methodology • clinical (human) or epidemiologic studies: systems/equipment/techniques 

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