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Comparative studies between species that do and do not exhibit the washout effect
Patrick A Scott1, Darryl R Overby, Thomas F Freddo
1Boston University School of Medicine, Boston, MA, USA.
Experimental Eye Research
|December 19, 2006
Summary
The "washout" effect, an increase in aqueous humor outflow facility, occurs in bovine but not human eyes. This difference is due to a unique "cribriform plexus" in human eyes that maintains tissue connection during perfusion.
Area of Science:
- Ophthalmology
- Biomechanics
- Fluid Dynamics
Background:
- Ocular perfusion studies show a perfusion-volume-dependent increase in aqueous humor outflow facility, termed the "washout" effect, in non-human species.
- This washout effect is notably absent in human eyes, suggesting a species-specific mechanism.
Purpose of the Study:
- To investigate the morphological basis for the absence of the washout effect in human eyes compared to bovine eyes.
- To test the hypothesis that the lack of washout in humans correlates with the absence of physical separation between the juxtacanalicular connective tissue (JCT) and inner wall endothelium.
Main Methods:
- Enucleated human and bovine eyes were subjected to short- or long-duration perfusion at 15 mmHg.
- Aqueous humor outflow facility was measured, and eyes were perfusion-fixed for morphological examination using light and electron microscopy.
Main Results:
- Bovine eyes exhibited an 81% increase in outflow facility due to washout, with significant JCT and inner wall/JCT separation observed in long-duration perfusion.
- Human eyes did not show the washout effect; long-duration perfusion led to a 40% decrease in outflow facility without significant morphological changes in JCT-inner wall connections.
- Human JCT contained an extensive
Conclusions:
- The
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