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Primary Open Angle Glaucoma - Part II

Created on: Thursday, November 15, 2012

Author:  Robert P. Friedlaender, M.D., See Clearly Vision

Signs and Symptoms Of POAG
The course of POAG is usually slow, painless, and progressive.  In the early stages POAG is usually asymptomatic. Optic nerve changes precede visual field changes, and are usually irreversible.  An attempt is made to correlate optic disc changes with visual field changes.  Optic nerve changes include loss of rim tissue, enlargement of the central physiologic cup, enlargement of the central cup to disc ratio, tiny hemorrhages on the surface of the disc, and changes in the blood vessels as they exit the optic disc.
 
Exam Findings In POAG
In POAG, there is usually increased IOP in both eyes, but occasionally only in one eye. The definition of what constitutes increased IOP is controversial, and may vary from patient to patient, depending upon how much the optic disc appears to be damaged, and to what degree the visual field is compromised.  The IOP is measured with an external pressure gauge (“tonometer”) that indents the cornea, and is measured in terms of units known as “millimeters of mercury” (or “mmHg.”).  Usually, IOP over 22 mmHg raises concern.  At 25 to 29 mmHg, a patient is designated as a “glaucoma suspect”.  Above 30 mmHg, therapy is usually recommended.  Patients with consistently borderline pressures within the mid to high 20’s, are also referred to as having “ocular hypertension”, and are followed at frequent intervals for conversion to full blown POAG.
 
Visual Field Defects In POAG
With progression of optic disc damage, there may be partial visual field loss peripherally, i.e. parts of a page missing.  With advanced disc damage, late in the disease, there can be tunnel vision with preservation of a central island of field, or sometimes even loss of central fixation. Once established, the visual field defects from POAG usually do not regress.  

While mild to moderately elevated IOP is asymptomatic, or unnoticed by the patient, symptoms of severely elevated IOP, at least over 40 mmHg, can be significant, and can include blurred vision, and severe pain at the eye brow (“brow ache”). High IOP can also cause disruption of the physiology of the corneal, resulting in retention of fluid within the normally clear cornea, producing a hazy cornea (“corneal edema”). However, such corneal changes are typical of the high pressures more characteristic of “Closed Angle Glaucoma”.  Extremely high pressure elevation is associated with the patient seeing haloes or rainbows around light bulbs, plus headaches and nausea.

Stay tuned for our next posting from Dr. Friedlaender, Primary Open Angle Glaucoma, Part III, which will discuss treatment and monitoring.


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