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To help you better understand the
following discussions on specific glaucoma topics you may need to first read
the FAQs on glaucoma found at
www.eye.com.ph/glaucoma.htm.
This information is provided for
your convenience and to help you understand your condition or procedure. It
is not meant to serve as a substitute for a discussion with your doctor
about the specifics of your condition, treatment, or procedure.
Classification
and Epidemiology of Glaucoma
The glaucomas can be classified
into two main types, namely, open angle glaucoma and angle closure glaucoma.
As the names imply, in open angle glaucoma the anterior chamber angle is not
manifestly occluded while in angle closure glaucoma the anterior chamber
angle is obstructed, usually by the iris.
Open angle and angle closure
glaucoma are each divided into primary and secondary types: primary open
angle glaucoma, primary angle closure glaucoma, secondary open angle
glaucoma and secondary angle closure glaucoma. Primary means there is no
identifiable cause for the glaucoma or the cause is inherent in the eye. The
term primary is used here in the same way that it is used for primary
hypertension. Secondary glaucoma means the glaucoma developed due to an
initial ocular or systemic disease. Let us take angle recession glaucoma as
an example. It is a secondary open angle type of glaucoma because it only
occurs if the eye sustained blunt force trauma first.
The primary glaucomas (primary
open angle and primary angle closure) are by far the most common of the
glaucomas. They are ranked first and second most common types of glaucoma in
almost all populations studied worldwide. In studies done on Caucasian,
Black, and Afro-Caribbean populations, primary open angle glaucoma ranks
first and primary angle closure glaucoma is a somewhat distant second. On
the other hand, in studies done on Chinese and South African populations,
primary angle closure ranks first while primary open angle ranks second. In
the Philippines there have been no population-based studies conducted that
have distinguished the different types of glaucoma from each other, but it
is estimated that the incidences of primary open angle glaucoma and primary
angle closure glaucoma are almost equal.
References:
Klein BEK et al.
Prevalance of glaucoma: the Beaver Dam Eye Study. Ophthalmology 1992;
99:1499.
Tielsch JM et al. Racial
variations in the prevalence of primary open-angle glaucoma: the Baltimore
Eye Survey. JAMA 1991; 266:369.
Foster PJ et al. The prevalence
of glaucoma in Chinese residents of Singapore: a cross-sectional population
survey of the Tanjong Pagar district. Archives of Ophthalmology 2000;
118:1105-1111.
Foster PJ, Johnson GJ. Glaucoma
in China: how big is the problem? British Journal of Ophthalmology 2001; 85:
1277-1282.
Salmon JF et al. The prevalence
of primary angle closure glaucoma and open angle glaucoma in Mamre, Western
Cape, South Africa. Archives of Ophthalmology 1993; 111:1263-1269.
Ritch R, Shields MB, Krupin T (Eds).
The Glaucomas, 2nd Edition. St. Louis, Missouri, USA, 1996, Mosby-Year Book,
Inc.
Epstein DL,
Allingham RR, Schuman JS (Eds). Chandler and Grant’s Glaucoma, 4th
Edition. Baltimore, Maryland, USA, 1997, Williams & Wilkins.
South East Asian Glaucoma
Interest Group. Asia-Pacific Glaucoma Guidelines. Sydney, Australia,
2003-2004, SEAGIG.
European Glaucoma Society.
Terminology and Guidelines for Glaucoma 2nd Ed. Savona, Italy, 2003, EGS.
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