8

classification of primary angle closure (PAC) discussed below.

PAC suspect

An eye in which appositional contact between the peripheral iris and posterior trabecular meshwork is considered possible.

PAC

An eye with an occludable drainage angle and features indicating that trabecular obstruction by the peripheral iris has occurred, such as peripheral anterior synechiae, elevated IOP, iris whorling (distortion of the radially orientated iris fibers), ‘‘glaucomfleken’’ lens opacities, or excessive pigment deposition on the trabecular surface. The optic disc does not have glaucomatous damage.

PACG

PAC together with evidence of glaucoma, as defined above.

Certain general conclusions can be drawn from the studies on glaucoma prevalence shown in Tables 1–3.

A constant finding in these prevalence studies is that most cases of glaucoma had not been previously diagnosed. This was first noted in the Ferndale study, where two thirds of the POAGs and three quarters of the PACGs were undiagnosed (Hollows and Graham, 1966). It is interesting to note that even in the most recently published studies the rate of undiagnosed glaucoma is particularly high: 33% in the United States (Friedman et al., 2006), 57% in Greece (Topouzis et al., 2008), 70% in Spain (Varma et al., 2004), 74% in China (He et al., 2006), 90% in Brazil and in South Africa (Sakata et al., 2007; Rotchford and Johnson, 2002), and from 91% to 98.5% in India (Ramakrishnan et al., 2003; Vijaya et al., 2005).

Another fairly constant finding is the discrepancy between the clinical and epidemiologic diagnoses of glaucoma, which emerged for the first time in the Framingham Eye Study (Leibowitz et al., 1980). In this study, visual-field defects were actually found in less than one fourth of the

patients who reported that they had been diagnosed with or were receiving pharmacological treatment for glaucoma. Later, in the Dalby Study, not even one of the 16 patients diagnosed with glaucoma before enrollment had visual-field defects: all had HIOP that was being treated ‘‘to prevent or anticipate glaucoma’’ and all of the cases of glaucoma were discovered only after enrollment (Bengtsson, 1981). This was an interesting public health issue that has unfortunately not been investigated in more recent studies.

In studies in which routine visual-field testing was not performed and IOP was used to define glaucoma, the prevalence of the disease was lower than that reported when routine field testing was used and POAG was not defined by IOP alone.

Methods of examination have changed markedly since the 1960s up to now. Variations in eye examination methods, case definitions, and the prevalence of primary glaucoma complicate the comparison of individual studies, but the most recent ones (see above) are easier to compare because they are abased on the three-tiered system of evidence (Foster et al., 2002). The prevalence of POAG has been increasing, and this trend is undoubtedly due at least in part to advances in diagnostic technology, which have led to earlier and more reliable identification of cases. It is also important to recall that many of the cases assigned to categories 2 and 3 of the classification developed by Foster et al. (2002) were previously described as ‘‘probable,’’ ‘‘suspected,’’ or ‘‘doubtful’’ before this classification system was introduced. However, it is impossible to exclude the possibility that these increases are due in part to increased life expectancies.

The decreasing prevalence of PACG is due to the adoption of more stringent criteria for the diagnosis of this form of glaucoma. In the past, the presence of a narrow drainage angle with an elevated IOP or peripheral anterior synechiae was sufficient for a diagnosis of PACG and the presence of glaucomatous field defects or optic disc changes were not considered mandatory for the diagnosis of angleclosure glaucoma (Jacob et al., 1998).

Prevalence increases proportionately with age for each racial group (i.e., prevalence increases