Glaucoma Pathophysiology
Glaucoma is a nonspecific term used to describe a group of diseases characterized by an increase in intraocular pressure with progressive optic nerve degeneration and visual field loss. Glaucoma can develop in one or both eyes at varying degrees. The presence of ocular hypertension does not determine the presence of glaucoma. Conversely, some people develop glaucoma with normal ocular pressures. Hallmark indicators along with diagnostics are needed to make a conclusive diagnosis of glaucoma.
The normal intraocular pressure (IOP) is between 12-20mm/Hg. Tonometry is the standard method of measuring the ocular pressure during a slit lamp exam. A slit lamp, or gondocsopy, examines the anterior chamber angle to measure the angle where the iris meets the cornea. It is measured to determine the space allowed for aqueous humor flow. Patients with suspected glaucoma should also have a perimetry evaluation to measure any damage done to the optic nerve. Perimetry is a computerized evaluation of the patient responses to the presence of objects or lights in different areas of their field of view. Optic nerve damage caused by glaucoma creates a visual field defect that is specific to the disease, and therefore can be used to air in diagnosis.
The most common forms of glaucoma, Chronic Open Angle Glaucoma (COAG) and Primary Open Angle Glaucoma (POAG), have no warning signs. Since progression can happen over the course of years, patients who do not have routine eye exams may not be aware of diminishing visual acuities. In late stages patients may experience tunnel vision or “patchy spots” in their vision. COAG is a progressive condition and damage done to the optic nerve is irreversible. COAG develops in the presence of an open anterior chamber on slit lamp exam, characteristic visual field abnormalities, and intraocular pressures that risk the continued health of the optic nerve.
Acute Angle-Closure Glaucoma (AACG), in contrast, is an ocular emergency. AACG is characterized by sudden acute ocular pain that increases with eye movement. This may involve only one eye but may be bilateral. The globe will feel firm upon palpation. Patients may experience nausea and or vomiting, headache, and a history of intermittent blurring of vision with or without halos. Higher pressures are associated with conjunctival injection, corneal edema and frequently a dilated nonreactive pupil or irregular shaped pupil. Slit lamp exam will show a narrowing or blockage of the normal angle.
Malignant Glaucoma is seen almost entirely in people who recently underwent ocular surgery. Symptoms may present shortly after surgery or develop symptoms months later. Patients often complain of blurred vision, and testing will reveal decreased visual acuity in the affected eye, often with the ability to detect hand movements only. Commonly, they are unable to identify numbers and letters on distance charts or near cards. An edematous and cloudy cornea may obscure the funduscopic examination. Patients may present with pain and discomfort, increasing redness in the effected eye, blurring, and obviously decreased visual acuity. Pain may be severe enough to cause nausea and induce vomiting, similar to an attack of acute angle-closure glaucoma.
Trauma is the most common cause of Hyphema Glaucoma. Usually a blunt, compressive force to the globe creates tears in the ciliary body, iris, and other anterior segment structures. Hyphema Glaucoma also may be caused by intraocular tumors, which may be benign or malignant. Corneal bloodstaining results from blood being forced into corneal endothelial cells, thereby “staining” the otherwise clear cornea. Bloodstaining is an ominous sign. The acute rise in intraocular pressure (IOP) is related to red blood cells clogging the outflow in the anterior chamber not by change in the angle. Pupillary reactions and ocular movements may be altered. The relative risk of developing AACG after ocular trauma associated with hyphema is high.
Glaucoma can be a visually devastating disease, with no reversal of optic nerve damage and should be thoroughly evaluation in any patient presenting with eye complaints. Rapid treatment and interventions are vital to preserving vision.
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