Glaucoma Introduction .Glaucoma describes a number of ocular conditions characterizedby: -1-Raised intraocular pressure (IOP).2-Optic nerve head damage(cupping).3-Corresponding loss of visual field (VF).•IOP depends on the relationship between aqueous productionand outflow.•The normal ocular tension is between 10-21mm.Hg. There is anormal fluctuation in ocular tension of up to 3-5mm.Hg. during thecourse of the day called diurnal variation.•Glaucoma remains one of the principal causes of blindnessthroughout the world
Anatomy of the drainage angleThe anterior chamber(AC)• is that space, containing aqueous humor, which is bounded infront by the cornea and part of the sclera, and behind by the irisand part of the ciliary body.•Its normal depth in adults varies from 2.5-3.5mm.•The angle of the anterior chamber.•refers to that peripheral recess bounded posteriorly by the root ofthe iris and the ciliary body and anteriorly by the corneo-scleraljunction or the limbus.Among the deeper lamellae of the limbus,•there is an annular channel, called the canal of Schlemm.•The canal is separated from the aqueous in the anterior chamberby the trabecular meshwork.
The trabecular meshwork is made up ofcircumferentially disposed flattened collagenousbands which criss-cross, leaving numeroustortuous passages through which the aqueoushumor drains from the anterior chamber to thecanal of Schlemm.The aqueous humor is a transparent colorlessfluid which fills the anterior and posteriorchambers of the eye. Its chief site of formation isthe processes of the ciliary body. The volume ofaqueous in the anterior chamber of the humaneye is 0.25 ml.
Classification of glaucoma.1-Angle configuration a-open(POAG=primary open angle glaucoma). b-Narrow/closed.(PACG=primary angle closure)2-Onset a-acute(acute congestive glaucoma)red eye differential diagnosis. b-Chronic(primary open angle glaucoma)3-Causes a-primary(POAG/PACG) or congenital/developmental glaucoma. c-acquired/secondary glaucoma(secondary openangle and secondary close angle…) Secondary to other ocular diseases.(neovascular glaucoma)in CRVO or in diabetic eye disease(lens induced)I neglectedcataract.
PRIMARY OPEN-ANGLE GLAUCOMA(POAG). Primary open-angle glaucoma (POAG) is characterized by the1-development of glaucomatous optic neuropathy in an eye with2-a normal-appearing mechanically opened anterior chamber angleand3- absence of other ocular or systemic disorders which may accountfor the optic nerve damage.4-Most cases of primary open-angle glaucoma are associated withstatistically elevated intraocular pressure. Primary open-angle glaucoma is also called chronic open-angleglaucoma or simple open-angle glaucoma. POAG is the most common form of glaucoma. It is typically a bilateral disease but may be asymmetric.
Risk factors: age(>40 y): positive family history; diabetes;myopia.Aetiology: Unknown. Theories suggest: functional inadequacy ofTM drainage; hypoperfusion of optic N. head; and weakness ofstructural collagen in the angle and disc.Symptoms: usually asymptomatic until late, when considerablefield loss has already occurred; not associated with pain,discomfort or redness; new cases are usually identified byscreening.Signs:IOP: usually elevated, even sometimes double the normal value,may be up to 40 mm hg.Visual field (VF): up to 50% of ganglion cell axons entering thedisc may be lost before disc and field changes are evident.Peripheral field is progressively lost, but central acuity is affectedlate.
Pathophysiology:Even today, much remains unknown about this disease.•Elevated IOP almost certainly plays a significant role, butthe process is poorly understood.• According to the mechanical theory of POAG,chronically elevated IOP distorts the lamina cribrosa,crimping the axons of retinal ganglion cells as they passthrough the lamina cribrosa and eventually killing thecells.•The vascular theory suggests that with elevated IOP,reduced blood flow to the optic nerve starves the cells ofoxygen and nutrients
Clinical Testing and Examination Techniques inGlaucoma1/TONOMETRY(intraocular pressure measurement-IOP)•Indentation Tonometry The Schiotz tonometer is the primary indentation tonometer used to measureintraocular pressure.• Applanation TonometryApplanation Tonometry uses a variable amount of force to produce a fixed amountof flattening of the corneal surface. Applanation Tonometry is based on theImbert-Fick principle, which states that the external force (F) exerted to a sphere,equals the pressure inside this sphere (P) times the area (A) which is flattened or"applanated" by the external force.2/GONIOSCOPY. is an examination technique used to visualize the structures of the anteriorchamber angle. Mastering the various techniques of Gonioscopy is crucial in theevaluation of the Pathophysiology of aqueous humor outflow obstruction and thediagnosis of the various glaucomas.3/FUNDOSCOPY.Disc: damage usually begins as an upper or lower temporal notch, giving rise to anasal arcuate scotoma,then progressive cupping can occur with progressive fieldloss
4/PERIMETRY(testing visual field loss) by static or kinetic devices.
Management Aims.Progressive disc cupping and field loss in POAG progress at avariable rate, leading in the most severe cases to profound fieldconstriction and ultimately blindness. The aim of management is to lower IOP sufficiently to arrestprogressive VF loss.1/Medical treatment: topical beta-blocker (Timolol,carteolol,betaxolol) /prostaglandinderivatives(latanoprost)/adrenergic agonist(brimonidine)/topicalcarbonic Anhydrase blockers(dorsolamide)andparasympathomimetics (pilocarpine).2/Surgical treatment: Trabeculectomy provides a definitive and permanent reduction ofIOP to within safe limits in the majority of cases.
References . 1-Parson’s disease of the eye 2003. 2-Lecture notes on ophthalmology, Bruce James, Chris Chew, ninth edition, Blackwell scientific 2003 3-Atlas of ocular pathology, ocular trauma, on CD. 2-Clinical ophthalmology Kanski J 2007 3-ophthalmology.a short textbook.Gerhard.k.Lang.T hieme publications.2000.