Tissues of the eye are highly specialized in order to permit light to enter and come to a focus at the posterior inner surface of the globe where it is detected by photoreceptors in the retina. Photoreceptor signals then undergo complex processing by the neural cells of the retina prior to transmission of the signal to the brain via the optic nerve. The forward-facing surface of the eye, the cornea, is transparent as is the lens which is positioned in the light path by suspensory ligaments that extend from the edge of the lens to a ring of tissue, the ciliary body, on the inner surface of the eyeball just behind the iris (see Fig. 1). Altered muscle tension in the ciliary body stretches or relaxes the suspensory ligaments of the lens, changing its shape to alter the focus of the eye for near or distant vision. Aside from the lens, the interior of the eye is filled with transparent fluids. Vitreous humor, a gel, occupies the space between the lens and retina. Aqueous humor, a watery fluid, fills the space between the lens and cornea. The principal difference between these two fluids is that the vitreous humor is static while the aqueous humor is continually turned over; fresh aqueous humor enters the eyeball from the ciliary body at a rate of 1–2 µliter/min, and there is a corresponding drainage of the fluid, mostly through the trabecular meshwork, a highly specialized structure located at the point where the periphery of the iris meets the inner wall of the eye.