Biomedical Engineering Reference
In-Depth Information
Fig. 2 Outflow pathways of the canine eye, other species are comparable.
Aqueous humor is made by the ciliary processes, flows into the posterior
chamber and through the pupil into the anterior chamber. From the anterior
chamber it may flow into trabecular meshwork and into the angular aqueous
plexus and be directed interiorly into more superficial episcleral venues (1) or
posterior into the scleral venous plexus and the vortex venous system (2) and
eventually into the general circulation. Alternatively, (3) aqueous may pass
through the ciliary muscle interstitial to the suprachoroidal space and diffuse
through the sclera (uveoscleral outflow) and enter the orbit. From Tsai S, Miller
PE, Strule C et al (2012) Topical application of 0.005 % latanoprost increases
episcleral venous pressure in normal dogs. Vet Ophthalmol 15 (suppl 1):71-78
the sclera) [
10
]. From these locations it passes through the sclera
into the orbit. In most species the majority of aqueous humor
(approximately 50 % in horses, 85 % in dogs, and 97 % in cats)
leaves the eye via the traditional outflow route [
1
].
The relationship between the various components of aqueous
humor production and outflow has been described by the following
equation [
11
]:
Flow in
¼
Flow out
Rate of formation
¼
Pressure gradient across entire outflow pathway
Ease withwhich fluid can exit
þ
uveosceral outflow
F
¼ð
P
i
P
e
Þ
C
þ
U
F
¼
rate of aqueous formation in
μ
l/min
P
i
¼
IOP in mmHg
P
e
¼
episcleral venous pressure in mmHg
C
¼
facility of aqueous outflow in
μ
l/min/mmHg
U
¼
Uveoscleral outflow (assumes is pressure independent)
