Glaucoma. Definition types and forms. Methods for examination Topic 51
The pathophysiology of glaucoma revolves around the aqueous humour dynamic.
And the ocular structures involved are the ciliary body, angle of anterior chamber and the aqueous outflow system.
The ciliary body produces the aqueous humour
The angle of anterior chamber (formed by the root of the iris ,so anterior most part of ciliary body ,scleral spur ,trabecular meshwork and schwalbe line
The angle which can be viewed by gonioscopic examination plays a big role in the pathomolgy of glaucoma.
There are different grading mechanisms
The aqueous outflow system includes the trabecular meshwork, Schlemm’s canal, and collector channels. Aqueous veins and the Episcleral veins.
The trabecular meshwork behaves like a sieve through which the aqueous humour leaves
Schlemm’s canal is an oval channel present in the scleral sulcus and its outer wall contains opening of collector channels.
Collector channels (aka intrascleral aqueous vessels) which leave the Schlemm’s canal and terminate into the Episcleral veins in two different ways either directly via aqueous veins or via intrascleral plexus which is indirect.
Physiology
It is important to know how the Aqueous humor is produced, drained and how it is relevant to Intraocular pressure (the major and main risk for developing glaucoma)
Production
=derived from plasma in ciliary processes by three mechanism diffusion, ultrafiltration and secretion via active transport (production rate of 2.3 microl/min)
The exact control is unknown but Ultrafiltration & diffusion depend on BP in ciliary capillaries plasma osmotic pressure and the level of intraocular pressure
It is an aqueous humour; it is clear, watery and it fills both the anterior (0.25 ml) and the posterior chamber (0.06ml) of the eyeball
It maintains intraocular pressure; it provides metabolites and removes waste from avascular cornea and lens, maintains optical transparency and functions like lymph
It is 99.9 water and only 0.1 solids ( some proteins but limited unless blood aqueous barrier is broken like in inflammation of uvea, AA,glugose, urea, lactic acids ,pyruvate and electrolytes Na K CL HCO3-)
It is similar to plasma composition but varies in concentration of pyruvate and lactate (high) and has low con of protein, urea and glucose.
The differences between aqueous anterior and aqueous posterior are that, aqueous p has more con of HCO3- and CL- but lower con of Ascorbate
Drainage of Aqueous humour
It flows from posterior into anterior through the pupil and from the anterior it is drained via two routes: