WHAT IS GLAUCOMA?
Glaucoma is a disease of the optic nerve often associated with increased intraocular pressure (IOP).
Elevated IOP alone is not enough to make the diagnoses of glaucoma. Some patients may have glaucoma when their IOP is within normal limits. This is called Normal Tension Glaucoma (NTG). Conversely many patients have IOP elevation and never develop glaucoma. This is called Ocular Hypertension (OHT).
If you are confused by this, don’t worry, you are not alone. Most patients and many physicians have difficulty understanding glaucoma. We are used to concentrating on numbers. Hypertension is defined as blood pressure above 140/90. Diabetes is followed by measuring the blood sugar and the hemoglobin A1C (HgbA1C). So it is natural for the IOP measurement to be the focus of glaucoma diagnoses and treatment.
But glaucoma is different from hypertension and diabetes. Aside from intraocular pressure measurements the function and structure of the optic nerve must be evaluated when evaluating glaucoma. Calling IOP measurements a “glaucoma test” and the use of IOP measurements in “glaucoma screenings” is inadequate and misleading.
The best way to evaluate a patient for glaucoma is:
- - Obtain a complete medical history including a review of systems and family history concentrating on a family history of glaucoma and a history of migraine.
- - Visual acuity, slit lamp exam, IOP measurement and careful examination of the optic disc are the minimum examination techniques required in glaucoma evaluation.
If the medical history is negative and the physical eye exam normal then this is an adequate “glaucoma screening.” IOP measurement alone is not good enough.
If the medical history is positive or the eye exam suspicious then further testing is necessary, such as ultrasonic pachymetry – measurement of corneal thickness, computerized visual field testing and photographic imaging of the optic disc. The optic disc is the portion of the optic nerve that is visible when looking at the ocular fundus, the inside of the eye.
I have only touched on the surface of glaucoma evaluation. More information is available here, here, here and here.
Noah Klein, MD
Noah Klein, MD, PC
August 13, 2009
January 3, 2010
This is another good link about glaucoma:
http://www.travatanz.com/High-Eye-Pressure.aspx
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