2012 Can J Ophth Cook & Foster- Whats New

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Epidemiology of glaucoma: what’s new?Colin Cook, FCS(Ophth)SA*, Paul Foster, FRCOphth†

ABSTRACT ● RÉSUMÉ

Globally, there are an estimated 60 million people with glaucomatous optic neuropathy and an estimated 8.4 million people who are blindas the result of glaucoma. These numbers are set to increase to 80 million and 11.2 million by 2020. Glaucoma is the second leadingcause of blindness globally. The highest prevalence of open-angle glaucoma occurs in Africans, and the highest prevalence ofangle-closure glaucoma occurs in the Inuit. Population-based screening for open-angle glaucoma is not recommended. Screening forangle-closure may be feasible.

À l’échelle mondiale, l’on estime à 60 millions le nombre de personnes atteintes d’une neuropathie optique glaucomateuse et à 8,4millions le nombre de cécités dues au glaucome. Ces données s’apprêtent à augmenter jusqu’à 80 millions et 11,2 millions en 2020. Leglaucome est la deuxième cause principale de cécité dans le monde. La prévalence la plus élevée du glaucome à angle ouvert se situechez les Africains et la prévalence la plus élevée du glaucome à angle fermé se situe chez les Inuits. Le dépistage des populations pourle glaucome à angle ouvert n’est pas recommandé. Le dépistage à angle fermé peut être faisable.

Definition of glaucoma A definition of glaucoma for use in epidemiologic stud-

ies was agreed on in 1998, and that definition is still inuse.1 Glaucoma is defined as an optic neuropathy that ischaracterized by specific structural findings in the opticdisc and specific functional deficits detected by automatedvisual field testing. Raised intraocular pressure (IOP) is stillrecognized as an important risk factor, but it is not a de-fining characteristic of the disease.

Glaucomatous optic neuropathy results from loss of neuraltissue and from posterior bowing of the lamina cribrosa. Thevertical cup-disc ratio (VCDR) can be used as an index of neuroretinal rimloss, andthe97.5thpercentileof theVCDRsof thenormal population could be considered the upper limit

of normal. From the available evidence, a VCDR of 0.7 is the97.5th percentile cut-off in all ethnic groups studied.2 If theVCDR is used alone, 2.5% of the normal population wouldbe defined as having glaucoma. To make this more robust, if visual field testing is not possible and theVCDRis used alone,the 99.5th percentile is used as the cutoff. A VCDR of 0.8 isused as the cutoff for the 99.5th percentile.

A field abnormality is considered if, on a Zeiss-Humphrey field analyzer plot using a threshold program with a 24-2 testpattern, there is an abnormal glaucoma hemifield test or a reproducible cluster of 3 nonedge points abnormal at the 5%level and of typical glaucomatous distribution.

Prevalence of glaucomaThere are 3 levels of evidence that can be used for the

diagnosis of glaucoma in cross-sectional surveys (Table 1).1

A number of glaucoma prevalence surveys have beendone in various racial groups (Table 2).3-32 There are sev-

eral problems in making meaningful comparisons among the surveys. They include variations in the methodology,in the quality of the data, and in the criteria used to identify cases. Quigley and colleagues published pooled-data anal-yses of glaucoma prevalence data in 1996 and in 2006.33,34

In the 2006 paper, they note the following:

● Sixty million people are affected by glaucomatousoptic neuropathy.

● Three-quarters of these people have open-angle glau-coma.

● Women are affected more than men (55% of open-

angle glaucoma, 70% of angle-closure glaucoma, and59% of all glaucoma).

● Asians are the largest group affected, comprising 47% of the total with all types of glaucoma and 87%of primary angle-closure glaucoma.

● Primary angle-closure glaucoma is more common inChinese people.

● Japanese people have the highest rates of glaucoma occurring within the statistically normal range of IOP for the population.

● The prevalence of primary open-angle glaucoma in white Europeans, Americans, and Australians issimilar.

● Africans in Africa, the Caribbean, and the UnitedStates have a higher prevalence of primary open-angle glaucoma than do Asians and Europeans.

Presented at the annual meeting of the Canadian Ophthalmology Soci-ety, June 2011, Vancouver, BCFrom the *Division of Ophthalmology, University of Cape Town, CapeTown, Republic of South Africa, and the †Moorfields Eye Hospital,London, England.

Originally received Jan. 26, 2012. Accepted Mar. 27, 2012Correspondence to Colin Cook, Division of Ophthalmology, H53 OMB,Groote Schuur Hospital Observatory, 7925, Cape Town, South Africa;

[email protected]

Can J Ophthalmol 2012;47:223–226

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CAN J OPHTHALMOL—VOL. 47, NO. 3, JUNE 2012 223

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● The prevalence of glaucoma is projected to increase with population growth and the aging of the popu-lation, and by 2020 it is expected that the number of affected people will have risen to 80 million.

Prevalence of blindness from glaucomaGlaucoma is the second leading cause of blindness

globally, after cataract. The 2010 global estimates are

that 4.5 million people are blind due to open-angleglaucoma and 3.9 million are blind due to angle-closureglaucoma. These numbers are set to rise to 5.9 and 5.3million, respectively, by 2020. Angle-closure glaucoma causes a greater proportion of blindness than open-angleglaucoma.34

Some surveys of glaucoma prevalence report the pro-portions of people with glaucoma who are blind. These

numbers vary from none in Sweden23 to 22% in South Africa.5 Data from blindness-prevalence surveys for which cause-specific data are given offer similar num-bers of people bilaterally blind as the result of glau-coma.33,35

Table 3—Risk factors for primary open-angle glaucoma

Race African people have a prevalence up to 5 timeshigher than other ethnic groups.Hispanic people have a more pronouncedincrease with age

Age There is an exponential increase with increasedage.

Refractive error There is an increased risk with high refractiveerror, both myopia and hypermetropia.

Central cornealthickness

There is an increased risk with thin centralcorneal thickness.

Optic disc diameter There is an increased risk with a large optic discdiameter.

Intraocular pressure There is an increased risk for onset andprogression with elevated IOP, and a decreasedrisk for progression with lowering of IOP.

Blood pressure There is less risk in young persons withhypertension and increased risk in olderpersons with hypertension.

Diabetes mellitus This was previously considered to be a risk factorbut is no longer.

Cardiovasculardisease

Cardiovascular disease and glaucoma areprobably closely related.

Physical activity There is an increased risk for low ocularperfusion pressure with low physical activity.

IOP, intraocular pressure.

Table 1—Levels of evidence for the diagnosis of glaucoma incross-sectional surveys

Level Evidence

1 VCDR or VCDR asymmetry 97.5th percentile of the normalpopulation plus visual field defect compatible with glaucoma

2 Severely damaged disc (VCDR 99.5th percentile of the normalpopulation) plus no reliable visual field obtainable

3 No view of opt ic disc plus IOP 99.5th percentile of the normal

population or evidence of previous filtering surgeryIOP, intraocular pressure; VCDR, vertical cup-disc ratio.

Table 2—Glaucoma prevalence surveys in various racial groups

Racial Group Year ofPublication

Location Age Range PACG (%) POAG (%) Secondary Glaucoma Reference

African 2000 Kongwa, Tanzania 40 0.59 3.1 0.15 42002 Hlabisa, South Africa 40 0.1 2.7 1.7 5

African origin 1969 Jamaica 35-74 Nil 1.4 0.35 61989 St Lucia 30 Nil 8.8 A few 71991 Baltimore, U.S. 40 0.67 4.74 1.42 81994 Barbados 40-84 Not stated 7.1 Not stated 9

African mixed origin 1993 Mamre, South Africa 40 2.3 1.5 0.81 10East Asian Asian

origin 1973 Umanaq, Greenland 40 4.8 1.26 1.00 111987 Alaska 40 2.65 0.24 Nil 121988 Alaska 40 3.8 Nil Not stated 131989 Beijing, China 40 1.4 0.03 Not stated 141991 Japan 40 0.34 2.62 0.48 151996 Taiwan 40 3.0 Not stated Not stated 161996 Hovsgol, Mongolia 40 1.4 0.5 0.3 172000 Singapore 40-79 1.14 1.79 0.57 18

Indian 1999 Hyderabad, India 30 0.71 1.62 0.21 19,2040 1.08 2.56 0.11 19,20

European origin 1966 Ferndale, Wales 40-74 0.09 0.43 0.26 211980 Framingham, U.S. 52-85 Not stated 1.9 Not stated 221981 Dalby, Sweden 55-69 Nil 0.86 0.34 231991 Middle Norway 65 Not stated 3.37 4.97 241991 Baltimore, U.S. 40 0.31 1.29 0.68 81992 Beaver Dam, U.S. 43-84 0.04 2.1 Not stated 251994 Roscommon, Ireland 50 0.09 1.88 0.41 261994 Rotterdam, Netherlands 55 Nil 1.1 Nil 271996 Blue Mountains, Australia 49 0.27 3.0 0.15 281997 Ponza, Italy 40 0.97 2.51 0.29 291998 Egna-Neumarkt, Italy 40 0.6 2.0 0.3 301998 Melbourne, Australia 40 0.1 1.7 0.2 31

American Hispanic 2001 Tucson, U.S. 40 0.1 1.97 0.02 32

PACG, primary angle-closure glaucoma; POAG, primary open-angle glaucoma.

Epidemiology of glaucoma— Cook & Foster

224 CAN J OPHTHALMOL—VOL. 47, NO. 3, JUNE 2012



Incidence of glaucoma and glaucoma blindnessKnowing the prevalence of eye disease and blindness

is useful when advocating for allocation of resources foreye care and blindness prevention. Knowing the inci-dence is more useful for planning services. However,incidence data are more difficult to obtain than preva-lence data.

To report observed incidence, it is necessary to conducta cross-sectional survey, wait a number of years, and thenre-examine the same population. The cumulative inci-

dence is calculated as the number of new cases in that timeperiod, divided by the total population at risk. In a pre-dominantly white population in Melbourne, Australia, the5-year incidence of definite open-angle glaucoma was0.5% and of probable and definite open-angle glaucoma was 1.1%.36 In a predominantly black population in Bar-bados, the 9-year incidence of definite open-angle glau-coma was 4.4%, or 0.5% per year.37 In both studies, theincidence rose with increasing age.

Estimates of incidence can be calculated from preva-lence data by using mathematical models.38,39 Based on a mathematical model, in the United States, the cumulative

probability of open-angle glaucoma in white persons is4.2% and in black persons is 10.3%.40

It would be useful to know the incidence of blindnessresulting from glaucoma, but these data are not available.In a study in Uganda, the annual incidence of visual lossresulting from glaucoma was 0.04%.41

Geographic distribution of glaucomaThe data in Table 1 give an indication of the differences

in prevalence rates and predominant types of glaucoma invarious populations and differing geographic areas.

Primary open-angle glaucoma is more common in Afri-cans than it is in Europeans or Asians. In the United States,the age-adjusted prevalence rate of primary open-angleglaucoma in African Americans is 4 to 5 times higher thanit is in European Americans. The highest reported preva-lence rates of primary open-angle glaucoma are in the black populations of the Caribbean.7,9

Angle-closure glaucoma is more common in Asians thanit is in Africans or Europeans. There is variation in theprevalence in the various areas in Asia; the highest preva-lence rates recorded are found in surveys of the Inuit.11-13

The risk factors for primary glaucoma are presented in

Tables 3 and 4.3,42-44

Screening for glaucomaScreening for glaucoma must include tests for both

open-angle glaucoma and angle-closure glaucoma. A screening test for open-angle glaucoma should be valid(with high sensitivity and specificity), reliable, inexpensive,rapid, and acceptable. Measurement of IOP and VCDR are 2 tests that are routinely used when screening for pri-mary open-angle glaucoma. They are continuous variables, with no cutoff point that discriminates adequately betweennormal eyes and eyes with glaucoma. There is no satisfac-tory combination of sensitivity and specificity for eithertest.45 A visual field defect does not become detectableuntil nearly 50% of the optic nerve fibres have atrophied. Itis a subjective test, and it may be unreliable. Therefore,screening of the general population for primary open-angleglaucoma using tonometry, disc examination, or visualfield examination cannot be recommended at the presenttime. Instead, the emphasis should be on opportunisticscreening of people at risk (for example, older Africans).

This is of interest and is important in low- and middle-income African countries where as much as 90% of cases of primary open-angle glaucoma may be undiagnosed and upto 50% of patients may already be blind in 1 eye at presen-tation.46

To screen for primary angle-closure glaucoma, 3 testshave been proposed that look for a shallow anterior cham-ber and an occludable angle: the oblique flashlight test, thelimbal anterior cha mber depth test, and the axial anteriorchamber depth test.47-49 The oblique flashlight test doesnot require a slit lamp, but it may be difficult to standard-ize. The limbal anterior chamber depth test and the axial

anterior chamber depth test do require a slit lamp, with allthe limitations that this imposes. Gonioscopy is requiredto confirm the diagnosis, and biometric gonioscopy using a reticule in the slit lamp’s eye piece has been found to beuseful.50 This is of interest and is of particular importancein areas of Canada and other locales where Inuit popula-tions reside.

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CAN J OPHTHALMOL—VOL. 47, NO. 3, JUNE 2012 225



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2012 Can J Ophth Cook & Foster- Whats New