Glaucoma

Intraocular pressure is determined by a balance between production and removal of aqueous humor   Aqueous is actively secreted into the posterior chamber by the ciliary process (non-pigmented epithelium), by a combination of active transport and ultrafiltration Filtration: As blood flows in the ciliary body's capillaries, it is coarsely filtered by the capillaries' endothelial cells. The resulting plasma is then refiltered by the pigmented and nonpigmented ciliary epithelial cells and is secreted into the posterior chamber 

Active transport occurring in the nonpigmented cilary epithelial cells induces small osmotic pressure gradients in between the cells. A higher concentration of solutes in the proximal part of the intercellular space generates a flow of water. The concentration diminishes from the proximal part to the distal part, releasing the liquid into the posterior chamber  It then passes through the pupil into the anterior chamber and leaves the eye predominantly through the conventional pathway

Conventional Pathway Aqueous humor exits the eye through the trabecular meshwork into Schlemm's canal It flows through 25–30 collector canals into the episcleral veins to reach the bloodstream  The greatest resistance to aqueous flow is provided by the trabecular meshwork, and this is where most of the aqueous outflow occurs Damage here raises the resistance and increases IOP in primary open angle glaucoma

Uveoscleral Pathway A small proportion of the aqueous (4%) drains across the ciliary body into the supra-choroidal space It is then absorbed into the venous circulation

Intraocular Pressure Intraocular pressure is determined by a balance between production and removal of aqueous humor  Normal range 10 - 21 mmHg Hypotony is defined as intraocular pressure equal to or less than 5 mmHg which could indicate fluid leakage and deflation of the eyeball IOP decreases at night due to the slower production of aqueous humor Raised IOP causes mechanical damage to the axons Raised IOP also causes ischemia of the axons by reducing blood flow at the nerve head 

Goldman Tonometer

against anesthesized cornea fluorescein is applied in the tear film 2 hemicircles are seen by the examiner force of contact is increased until the inner borders of the hemicircles just touch - endpoint the endpoint at which a fixed amount of the cornea is achieved

Perimeter  

accurate plotting of the visual field kinetic VF - patient indicates when he first sees a light of a specific size and brightness brought in from the periphery static VF - patient indicates when he first sees a stationary light of increasing brightness, presented anywhere in the visual field useful in chronic ocular and neurological conditions, to monitor changes in the visual field