Exfoliation Syndrome and Exfoliative Glaucoma 205In particular, over half of open-angle glaucoma cases may be due to XFG in
countries such as Norway, Iceland, Greece, Turkey and Saudi Arabia [7,8].
The prevalence of XFS in the United States is generally comparable to
that in Western Europe but significant racial variations exist, since the
condition is much more prevalent in whites than persons of African origin, and
Spanish-American men are almost six times more likely to have XFS
compared to non-Spanish-Americans [36,39].
It is puzzling that local variations in prevalence of exfoliation can be
remarkable. In Nepal, for example, XFS was detected in 12% of the members
of the Gurung ethnic group, but only in 0.24% of age-matched non-Gurungs
[39]. Similarly, in the Middle Norway survey XFS prevalence values of
10.2%, 19.9% and 21% were observed in three population cohorts from
different municipalities who were examined simultaneously using the same
criteria, even though the municipalities were lying only about 100 kilometers
apart [40]. Obviously, the interplay of genetic and environmental factors
(epigenetics) is a major determinant of exfoliation prevalence. Well-designed
population-based studies rather that frequency reports or studies with
convenience samples are needed in order to explore possible etiological
associations.
CLINICAL CHARACTERISTICS OF XFG
Patients with XFG are typically older than patients with primary open-
angle glaucoma (POAG) [13,19]. In fact, XFG is very uncommon before the
age of 50. Because XFG has a fast rate of progression, serious visual
deterioration or even terminal damage is often seen in some patients at
diagnosis, occasionally with remarkable inter-eye asymmetry [13,23]. Since
IOP is typically very high in eyes with XFG, subjective symptoms reported by
patients may include dull ocular or retrobulbar ache, clouding of vision due to
corneal edema, or sudden severe visual deterioration due to branch- or central
retinal vain occlusion [41,42]. However, most XFG patients do not experience
symptoms. IOP characteristics in XFG deserve particular mention: these eyes
usually have higher mean, higher peak and larger 24-hour and intervisit IOP
fluctuation compared to eyes with POAG [43-45]. Furthermore, IOP peaks in
eyes with XFG often occur outside office hours and can therefore remain
unnoticed in typical clinical settings [45,46]. As a consequence, single daytime
IOP measurements every few months may be inadequate as a means of
evaluating a patient’s overall IOP characteristics or the response to therapy. In