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C CLINICAL RESEARCH

REGIONAL DISTRIBUTION OF EYE CARE PROVIDERS AND INCREASING GLOBAL PREVALENCE OF GLAUCOMA
It is difficult to examine global projections and trends regarding primary open angle glaucoma (POAG) because
there is so much variation in the literature with respect to study design, examination methods and disease defini-
tions. However, with the North American population growing and also aging, it is not surprising that the number of
individuals with glaucoma is projected to continue to rise. Canada should be prepared for a significant increase in
glaucoma burden by 2040.

Recent scope expansion within the profession of optometry in Canada has broadened optometry’s role in glaucoma man-
agement and positioned the profession to help with the growing demands of eye health care. A 2015 study investigated the
regional variation in distribution of optometrists and ophthalmologists in major cities across Canada. The investigators
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looked primarily at the census metropolitan areas (cities > 100 000 people) and census agglomerates (cities ≥ 50 000) and
found that in these larger cities on average, for every 100 000 people there are 3.4 ophthalmologists and 16.5 optometrists.
When considering subspecialties within ophthalmology, the ratios break down to 1.9 comprehensive ophthalmologists and
1.5 subspecialty ophthalmologists for every 100 000 people. The ideal ratio of optometrists needed to best address the in-
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creasing population and disease prevalence is unknown, but based on absolute numbers in these regions alone, optometry
is well positioned to fill this need.
The purpose of this evidence-based guideline is to create a basic framework upon which Canadian optometrists can
continue building their competence and confidence in managing primary open angle glaucoma.

PRIMARY OPEN ANGLE GLAUCOMA (POAG)
The most basic classification of glaucoma is based upon examining the anterior chamber angle structure and classify-
ing the disease as open or closed angle glaucoma. Both open and closed angle glaucoma can be further sub-classified
into primary and secondary etiologies, with secondary glaucoma resulting from other ocular or systemic disease, trau-
ma, or the use of certain drugs. POAG is the most common form of the disease in North America. By definition it is the
development of glaucomatous optic neuropathy without any underlying cause. It is often a bilateral disease, but can
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be quite asymmetric. Elevated intraocular pressure (IOP) no longer has a place in the definition of glaucoma; in fact,
it is estimated that up to 50% of individuals with POAG have IOPs less than 22mmHg at presentation. Despite this,
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intraocular pressure remains the single most important modifiable risk factor for glaucoma and a significant predictor
of progression to vision loss. 11-13 Indeed, the higher the IOP, the more likely the development of optic nerve damage.
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Conversely, lowering IOP can significantly delay the onset of glaucoma and reduce the risk of progression. 14,15
In 2014, the global prevalence of glaucoma was estimated to be 3.5%, with 3.0% being classified as POAG and 0.5% as
primary angle closure glaucoma (ACG). Compared to 2010 numbers, it is estimated that the number of people with
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glaucoma globally will increase by 18.3% by 2020 (to 76 million persons) and by 74% by 2040 (to 111.8 million persons).
As a largely asymptomatic disease, POAG is often referred to as a “silent thief of vision” but vision loss may be slowed if
the disease is detected early in its course. In 2010, the World Health Organization reported that 7.6 million people were
blind from glaucoma: 4.3 million from OAG and 3.3 million from ACG. By 2020, the number of people blind due to glau-
coma is projected to increase to 11.5 million, with 5.9 million due to OAG. The majority of this increase in blindness is pro-
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jected to be in Asia and Africa, which can partially be attributed to the significant population growth in these countries. 16
NATURAL PROGRESSION OF POAG
The natural progression of POAG is generally fairly slow but a small minority of patients will progress rapidly. 17,18
Knowing the natural history is helpful in understanding the amount of damage that might occur if treatment is
delayed, and in deciding on appropriate follow-up intervals for patients diagnosed with or at risk of glaucoma.
Both the Early Manifest Glaucoma Trial (EMGT) and Collaborative Normal Tension Glaucoma Study (CNTGS)
included one cohort of patients with early to moderate glaucoma not started on treatment. 13,19 Both studies found
that individuals with normal tension glaucoma (NTG) progressed considerably slower that those individuals with
high tension POAG (HTG). 17

In the EMGT, the median time to glaucoma progression was 3.5 years in the high pressure group (HTG) and 5
years in the NTG group. On average, individuals with exfoliation syndrome progressed earlier and significantly
faster than individuals with primary open angle glaucoma. However, in both the HTG and NTG groups, there was
a minority that progressed quite rapidly. Identifying ‘rapid progressors’ as early as possible is important in order
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to initiate or alter treatment promptly and aggressively to prevent further vision loss. The EMGT also found that,
in general, progression rates were significantly faster in older individuals (-1.48dB/year) than younger individuals

6 CANADIAN JOURNAL of OPTOMETRY | REVUE CANADIENNE D’OPTOMÉTRIE VOL. 79 SUPPLEMENT 1, 2017