For better understanding we can say that the eyeball is like a capsule formed by 3 layers or spheres, one inside the other. The most external one is the white sclera that can be seen with the naked eye, its function is to give resistance to the balloon, and the front of it has a transparent circular portion that is the cornea.
The intermediate sphere is the uvea, this is the vascular layer in charge of nourishing the sclera and the retina, which becomes the innermost layer, capturing light and transmitting images to the brain. The uvea also produces the liquid that fills the chambers of the eye, which is derived from the blood; but when the uvea is inflamed, the production of liquid may decrease, causing a drop in intraocular pressure and allowing the entrance of liquid mixed with proteins and blood cells, which causes turbidity, internal hemorrhage or the formation of pus.
Uveitis is an external cause of redness of the conjunctival membrane, and internally, can be the cause of cataracts, glaucoma or retinal detachment.
