1. Describe mechanisms regulating aqueous outflow. 
Aqueous outflow is affected by the:

a. trabecular meshwork

  • the main bulk of aqueous drains through this pressure dependent system
  • the pressure difference between the intraocular pressure and the pressure within the episcleral vessels affects the drainage
  • drainage increases with increased intraocular pressure and low episcleral vessels and decreases with low intraocular pressure or high episcleral vessels (as in Valsalva's manoeuvre or blockage of the superior vena cava)
  • the position of the iris can affect the flow of aqueous, when the pupil is constricted, the trabecular meshwork opens wider and offers more areas for active transport. Conversely, the iris in a dilated pupil can impede aqueous drainage.
  • the main resistant is offered by juxtacanalicular layer of the trabecular meshwork
  • aqueous enters the Schlemm's canal by a process of phagocytosis. 
  • from the Schlemm's canal the aqueous leaves the eye via the episcleral vessels

b. uveoscleral system

  • about 10 to 30% of aqueous drains through this system.
  • it is pressure independent
  • intercellular space between the ciliary muscle fibres and the loose connective tissue of the suprachoroidal space.
  • aqueous reaches the suprachoroidal space and leave the eye either through the sclera or large vessels leaving the sclera.
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