The Prevalence of Glaucoma in the Melbourne Visual Impairment Project

Matthew D. Wensor, BOrth, Cathy A. McCarty, PhD, MPH, Yury L. Stanislaosky, PhD, MBBS, Patricia M. Livingston, PhD, Hugh R. Taylor, MD, FRACO

Purpose: The purpose of the study was to determine the prevalence of glaucoma in Melbourne, Australia. Methods: All subjects were participants in the Melbourne Visual Impairment Project (Melbourne VIP), a population-

based prevalence study of eye disease that included residential and nursing home populations. Each participant underwent a standardized eye examination, which included a Humphrey Visual Field test, applanation tonometry, fundus examination including fundal photographs, and a medical history interview. Glaucoma status was determined by a masked assessment and consensus adjudication of visual fields, optic disc photographs, intraocular pressure, and glaucoma history.

Results: A total of 3271 persons (83% response rate) participated in the residential Melbourne VIP. The overall prevalence rate of definite primary open-angle glaucoma in the residential population was 1.7% (95% confidence limits = 1.21, 2.21). Of these, 50% had not been diagnosed previously. Only two persons (0.1%) had primary angle-closure glaucoma and six persons (0.2%) had secondary glaucoma. The prevalence of glaucoma increased steadily with age from 0.1% at ages 40 to 49 years to 9.7% in persons aged 80 to 89 years. There was no relationship with gender. The authors examined 403 (90.2% response rate) nursing home residents. The age standardized rate for this component was 2.36% (95% confidence limits = 0, 4.88).

Conclusion: The rate of glaucoma in Melbourne rises significantly with age. With only half of patients being diagnosed, glaucoma is a major eye health problem and will become increasingly important as the population ages. Ophthalmology 1998; 105:733-739

Glaucoma is a major cause of visual loss worldwide. It has been estimated that approximately 22.5 million persons suffer from some form of glaucoma, more than 5 million of these are blind from the disease.‘,* This represents approximately 15% of global blindness, the third most prevalent after cataract and trachoma.“* As a result, glaucoma has been the subject of many popula- tion-based prevalence studies around the world. It generally has been accepted by investigators that the prevalence of glaucoma increases with age,“-14 and most studies agree that primary open-angle glaucoma (POAG) is more prevalent than primary angle-closure glaucoma in white populations, whereas the opposite is true in southeast Asia.“-“,” The aim of the current study is to describe the distribution of glaucoma in urban Melbourne, Australia.

Originally received: January 28, 1997. Revision accepted: October 7, 1997.

From the Department of Ophthalmology, University of Melbourne, Mel- bourne, Austraha.

Supported by the Victorian Health PromotIon Foundation, Melbourne, the Ansell Ophthalmology Foundation, Melbourne, the National Health & Medical Research Council, Canberra, the Ophthalmic Re- search Institute of Australia, Sydney, Dorothy Edols Estate, Melbourne, and Carl Zeiss Pty Ltd, Sydney, Australia.

Reprint requests to Cathy McCarty, PhD, MPH, Epidetruology Research Umt, Department of Ophthalmology, University of Melbourne, Royal Victorian Eye and Ear Hospital, 32 Gisborne Street, East Melbourne, Victoria, Australia, 3002.

Methods

The Melbourne Visual Impairment Project (Melbourne VIP) is a population-based prevalence study of the distribution and determinants of eye disease in Melbourne, Australia. The meth- ods have been described in detail previously.” Melbourne is Australia’s second largest city, with a population in 1991 of 3.02 million.” Other than those born in Australia (68%), Mel- bourne’s major cultural groups are from the United Kingdom (6%), Italy (3.1%), Greece (2.1%), Vietnam (IS%), and New Zealand (1.2%)‘”

The participants in the Melbourne VIP were residents aged 40 and older from nine pairs of randomly selected 1986 Austra- lia Bureau of Statistics Census Collector Districts in Melbourne.

Each participant was contacted by field interviewers through a household census, asked a question regarding demographic details and health service use, and invited to attend a local screening center for an eye examination. The examination in- cluded visual acuity testing, subjective refraction, visual field testing, assessment of the anterior chamber depth, measurement of intraocular pressure (IOP), and a standardized clinical assess- ment.

Visual fields were measured using the Humphrey Field Ana- lyzer (Carl Zeiss, San Leandro, CA). For the first 2.55 partici- pants, the 80-point suprathreshold test was used. If the field was deemed suspicious, that is, 3 depressed points or 2 adjacent depressed points, a 24-2 Fastpac test was completed, which occurred in 81 participants. This was found not to save time substantially as compared to using the Fastpac 24-2 program on every participant. The Fastpac 24-2 threshold test subse- quently was used because it was found to be comparable to the full-threshold 24-2 test but 32% to 39% faster.17 If the

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Ophthalmology Volume 105, Number 4, April 19%

Table 1. Criteria for the Consideration at Glaucoma Consensus Meeting

Past history of glaucoma IOP >21 mmHg in either eye Visual field defects: nasal step >5 dB tn three adjacent points or > 10

dB m 2 adjacent pomts Any bundle-type defect Enlarged blmd spot

Enlarged (20.7) and/or asymmetrical (20.3) cup/disc rato

IOP = mtraocular pressure.

ophthalmologist suspected the result contained a visual field defect, the test was repeated. If it was impossible or impractical to obtain a Humphrey Visual Field, a Bjerrum field was per- formed (done on 60 right eyes and 61 left eyes). I f this also was unobtainable, a confrontation field was done (12 cases).

Intraocular pressure was measured after the instillation of one drop of oxybuprocaine hydrochloride (0.4%) in each eye. The measurement was taken with the Tonopen (Oculab, La Jolla, CA) and repeated if the result was 21 mmHg or greater (3.6% right eyes and 2.8% left eyes). I f it was confirmed to be greater than 21 mmHg, the reading was checked with a Gold- mann applanation tonometer, and this measurement was taken as final. Unreliable (4 right eyes and 6 left eyes) or difficult (10 right eyes and 12 left eyes) measurements were recorded as such. Dilation was achieved using one drop of tropicamide (0.5%) and one drop of phenylephrine hydrochloride (10%) instilled in each eye.

The fundus was examined on a slit lamp using a 90-diopter convex lens and included measurement of vertical cup/disc (C/ D) ratio. This data were used in the C/D ratio analyses. Photo- graphs of the fundus were taken using a Topcon TRC FET retinal camera (Topcon, Paramus, NJ) on Kodachrome 64ASA color film (Kodak, Harrow, UK). Paired stereo photographs of the optic disc and the macula were taken and subsequently assessed through stereo viewers. There were 4.9% considered ungradable because of poor quality, atypical disc structures, or lack of optic disc in photographs.

The actual diagnosis of glaucoma is problematic because of the uncertainty of diagnostic criteria. To ensure accurate diagnosis, records of those persons who were regarded as glau- coma suspects (Table 1) were compiled and presented to a glaucoma consensus meeting. Present at the meeting was a panel of six experienced ophthalmologists that included two glaucoma subspecialists and was organized and chaired by the field oph- thalmologist. The panel graded the visual fields and optic disc photographs independently and in a masked fashion. The final classification for each individual was decided using all available data for that person, and each diagnosis was ranked on a scale of certainty; either none (0), possible (l), probable (2), or defi- nite (3). Each expert used his or her own clinical judgment to classify each case. Therefore, no specific criteria were used. Cases that had significant discrepancies between experts’ opin- ions were resolved in open discussion. Cases considered for open discussion had a difference of two steps or greater on the glaucoma certainty scale, had no clear majority diagnosis, or were specifically requested to be discussed by at least one of the panel members.

To include institutionalized persons, residents of 13 nursing homes were studied. These nursing homes were randomly se- lected and were all located within 5 km of a test site. The testing procedure had to be modified somewhat because of the difficulty

734

of testing elderly institutionalized individuals, such as the use of confrontation visual field testing instead of the Humphrey Field Analyzer and, in most cases, disc photography was not possible. The final glaucoma diagnosis was made on the basis of the clinical examination and visual field testing by the single clinical examiner who also was the examiner on the residential group. For these reasons, the data from the two components are not directly comparable.

All statistical analyses were performed with Statistical Anal- ysis Software version 6.10 (Cary, NC). Analysis of data con- taining one continuous dependent variable was performed using unpaired t tests, and extraneous variables were controlled for using general linear models. Correlation and regression analyses were performed on data containing two continuous variables.

Prevalence rates were directly age standardized against the Melbourne residential age distribution and 95% confidence lim- its (CL) calculated according to the method of Breslow and Day.18 The Melbourne VIP age distribution was used as the standard population. The variance estimates were calculated to account for the cluster sampling as presented by Cochran.” A P value of less than 0.05 was considered statistically significant.

Results

Residential Group

A total of 3271 persons attended the Melbourne VIP, an 83% response rate. A comparison between participants and nonparti- cipants showed that they were similar in all aspects except that non-English-speaking persons were shghtly less likely to attend.”

Of the 3271 persons, 6 did not have complete information on IOP, C/D ratios, visual fields, or glaucoma history and there- fore were excluded. This left 3265 for analysis. Data were miss- ing on visual fields for 23 persons, for IOP in 50 persons, and for C/D ratios for 63 persons.

The population consisted of 1509 males and 1756 females. The ages of the participants ranged between 40 and 98 years with the mean age being 58.7 (Table 2). Apart from those born in Australia (54.6%), the other major subgroups were from Italy (10.3%), the United Kingdom (9.6%), Greece (6.3%), Malta (1.7%), Egypt (1.2%), and Vietnam (0.5%).

There were 112 persons (3.4%) with POAG. Of these, 56 (1.7%) were regarded as definite, 16 (0.5%) as probable, and 40 (1.2%) as possible glaucoma sufferers.

Analysis regarding the agreement between glaucoma panel- ists on the glaucoma diagnosis scale (i.e., none, possible, proba-

Table 2. Age and Gender Distribution Study Populations*

Age Group Residential Nursing Home

(w) Males Females Males Femaks

40-49 357 (23.7) 466 (26.5) 1 (1.2) 2 (0.6) 50-59 446 (29.6) 531 (30.2) 2 (2.4) 4 (1.3) 60-69 426 (28.3) 435 (24.8) 15 (17.7) 9 (2.8) 70-79 221 (14.7) 222 (12.6) 28 (32 9) 68 (21.4) 80-89 56 (3.7) 89 (5.1) 30 (35.3) 155 (48.7) 90+ 3 (0.2) 13 (0.7) 9 (10.6) 80 (25.2)

Total 1509 1756 85 318

* Values are no. (%).

Wensnr et al * Prevalence of Glaucoma in the Melbourne VIP

Table 3. Primary Open-angle Glaucoma (POAG) Prevalence by Age Group and C&&r in Kesldentlal Population

Age Group (yd Population

Prohahle POAG Possible POAG All POAG

40-49 823 50-59 978 60-69 863 70-79 445 80-W 145

90+ 17

TLS.Il 3265

I (0.3) 0 (0) I (0.1) 3 (0 7) 3 (0 6) 6 (0.6) 9 (2 1) 7 (1 6) 16 (I 9)

IO (4.5) 13 (53) 23 (5 2) 3 (5.4) 5 (5.6) 8 (5 5) 0 (0) 2 (14 3) 2 (II.81

26 (1.7) 30 (I 7) 56 (I 7)

2 (0 5) 7 (1 6) 9 (I 0) I (0.5) 2 (0.9) 3 (0 7)

0 (0) 2 (3.6) 2 (1.4) 0 (0) 0 (0) 0 (0)

5 (0.3) II (0.6) I6 (0 5)

2 (0 6) 1 (0.2) 3 (0.4) 6 (1 4) I(O2) 7 (0.7)

II (26) 3 (0 7) 14 (1.6) 7 (3.2) 5 (2.2) 12 (2 7) 2 (3.6) 2 (2.3) 4 (28) 0 (0) 0 (0) 0 (0)

28 (1.8) I2 (0 7) 40 (I 2)

3 (0.X) l(O2) 4 (0.5) II (2 5) 4 (0 H) Ii (1.5) 22 (5 2) 17 ii 9) 39 (4.5) IX (8 I) 20 (9.0) 3s (S 6)

5 (8.9) 9 (IO I) 14 (9 7) 0 (0) 2 (14 3) 2 (II 8)

59 (3 9) ii (30) 11!(34)

ble, and definite) showed that all six agreed in 8.1% of cases, a difference of one step occurred in 37.5% of cases, two steps in 34.6% of cases, and three steps in 18.4% of cases on initial grading. There were 36.8% of cases that subsequently were adjudicated.

The prevalence of detinite POAG in the Melbourne VIP is therefore I .7% (95% CL = I .2 I, 2.2 I). In addition, two persons (0.1%) had primary angle-closure glaucoma and six persons (0.2%) had secondary glaucoma. One person (0.03%) was blind from glaucoma according to the World Health Organization definition of visual field constriction with less than IO” re- maining. The prevalence of glaucoma increases steadily with age (f’ = 32.01, P < 0.0001) but does not show any signiticant relationship with gender (f’= 2.06, P = 0. IS 17). The distribution of POAG by age and gender is listed in Table 3. The mean age of persons with glaucoma was 7 I, I years compared to the over- all cohort mean of 58.7 years.

Only 28 (50%) of those with definite POAG had been diag- nosed previously compared to 6 (38%) of those with probable glaucoma and 8 (22%) of those with possible glaucoma. Glau- coma medication was being taken by 41 persons, only 20 of whom were regarded as definite glaucoma cases and 21 persons who had undergone glaucoma surgery ( I7 definite glaucoma cases, 2 probable glaucoma cases, and I possible glaucoma case). Additionally, 25 persons (0.8%) who were classitied as having no glaucoma based on examination results reported a previous diagnosis of the disease (these were all classified by us as either ocular hypertensives or “presumed” ocular hyper- tensives, that is, normal IOP with previous or current glaucoma treatment), whereas I 1 (0.3%) of these persons reported current use of glaucoma medication and I (0.03%) reported glaucoma surgery.

Of the 56 persons with POAG, 29 (51.8%) were born in Australia, 7 (12.5%) in Italy, 5 (8.9%) in the United Kingdom, 4 (7.1%) in Greece, 3 (5.4%) in Malta, and 8 (14.3%) in other countries. These percentages were not significantly different from each countries’ overall representation in the entire sample population.

Both of the persons with primary angle-closure glaucoma were females and were 70 and 71 years of age. Of the six persons with secondary glaucoma, three were male and three were female. The youngest of these was 60 years old and the oldest was 78 years old. Four secondary glaucoma cases were iatrogenic: two being complications of cataract surgery, one a complication of retinal detachment surgery, and another being the result of a cornea1 graft. Of the remaining two, one was caused by uveitis and the other a result of trauma.

Intraocular pressures for the right eye ranged between 3 mmHg and 40 mmHg with the mean being 14.31 mmHg (Fig I). Results for the left eye were similar and are not presented. Forty-eight persons (0.9%) had IOPs of greater than 2 I mmHg.

Sixteen persons (0.5%) had IOP greater than 2 I mmHg and had no clinical signs of glaucoma (i.e., ocular hypertension) and 21 persons (0.6%) had normal IOPs and had no clinical glaucoma- tous signs but reported current or previous glaucoma treatment (presumed ocular hypertension).

Of those with glaucoma, 21 persons (39%) had pressures in both eyes of less than 21 mmHg and had neither a history ol glaucoma surgery nor were using glaucoma medication. Intraoc- ular pressure showed no significant relationship to age or gender but was correlated strongly with glaucoma diagnosis (t = 4.5X. P < 0.0001). Mean IOP in persons with glaucoma was 17.2 mmHg compared to 14.3 mmHg in the rest of the population (Table 4). The mean IOP of persons with glaucoma who pre- viously were undiagnosed was 19. I mmHg, significantly highcl than persons with previous diagnosis of the disease (t = 2.40. P < 0.05).

The comparison between the Tonopen and the Goldmann applanator was done with Spearman’s correlation coefficient (1 = 0.6 I). The mean pressure for the Tonopen was 2 I .5 I mmHg (95% CL = 20.39, 22.62) compared to the Goldmann applana- tor, which was 19.78 mmHg (95% CL = 18.49, 21.07). There- fore, there was no significant difference between the two.

The C/D ratios for the right eye ranged between 0 and I .O with a mean of 0.38 and a standard deviation of 0.23 (Fig 2). Again, the left eye results were very similar. The mean C/D ratio for glaucoma sufferers was 0.74 with a standard deviation of 0.28 (Table 4). There was no significant difference in C/D ratio between those glaucoma sufferers with previous diagnosis and those without (t = -0.1378, P = 0.8909). The C/D ratio was significantly higher in persons with POAG (t = 9.84, P < 0.000 I).

There was no significant relationship between C/D ratio and age or IOP, but there was a tenuous association between C/D ratio and gender in which males (mean = 0.39) were slightly higher on average than females (mean = 0.36). Although statis- tically significant (t = 3.57, P = 0.0004), this relationship is of questionable clinical significance because the difference in the means is only 0.03 and gender only predicts 0.69% of variation in C/D ratios (r’ = 0.0069).

Nursing Home Group

A total of 403 persons of a possible 447 participated in the nursing home study, a 90.6% response rate. The population consisted of 85 males and 3 I8 females, a ratio of almost I :4. The ages of the residents ranged between 46 and 101 with a mean age of 82.2 (Table 2).

There were 27 persons (6.7%; CL = 4.2,9.2) who were considered to have glaucoma. For nine (33.3%) of these persons who were blind according to World Health Organization guide-

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Ophthalmology Volume 10.5, Number 4, April 1998

800

700

600

18R.EI

Figure 1. Dlstributton of intra- ocular pressure for the right and left eyes.

500 No. of eyes

400

300

100

0

4 6 8

lines, glaucoma was considered to be the major cause of visual loss.

The IOP in the sample ranged between 4 and 50 mmHg with the mean being 14.4 mmHg (right eye only). The mean of those who had glaucoma was 19.0 mmHg.

The C/D ratio ranged between 0 and 1.0, with a mean of 0.41 (right eye). The C/D ratio mean for those suffering from glaucoma was 0.87.

The crude rate of POAG was higher in the nursing home group, but direct standardization showed no significant differ- ence in glaucoma prevalence between the residential (1.7%) and nursing home (2.36%) populations (Table 5). The combined adjusted glaucoma rates for the residential and the nursing home groups show prevalence rates of 1.72% in males and 1.91% in females older than 40 years of age.

Discussion

The overall prevalence of definite POAG cases in persons older than 40 years of age in the Melbourne VIP was

10 12 14 16 18 20 22 24 26 28 30+

mmHg

1.7% (95% CL = 1.21, 2.21). This rate is similar to other prevalence studies around the world (Table 6).

It has been noted that blacks have a higher rate of POAG than whites,3,4 and it can be seen that the studies with the two highest overall rates of POAG*,‘” included large black populations. However, this is not the case in a study in South Africa that included many indigenous Africans but also a large southeast Asian population in which the overall rate was only 1.5%.” The rates from the Baltimore Eye Survey and the Blue Mountains Eye Study on initial perusal appear twice as high, but these figures included definite and probable glaucoma cases (Table 6). The comparable rate in the Melbourne data is 2.2%.

The rate of primary angle-closure glaucoma in the Mel- bourne VIP was very low, accounting for only 0.1% of the population. This concurs with many other studies in so far as the rate of POAG far outweighing the rate of primary angle-closure glaucoma.“,s~6~xx9 Studies with

Table 4. Intraocular Pressure (Right Eyes), C/D Ratio (Right Eyes), and C/D Ratio Difference between Eyes for Glaucoma Status: Mean (SD)

Glaucoma Status Population IOP in Right Eyes C/D Ratio in Right Eyes Mean C/D Ratio Difference

Defmite POAG Probable POAC Possible POAG Definite POAG not previously

diagnosed PACG Secondary glaucoma Ocular hypertension Presumed OH* None

56 16 40

28 2 6

16 21

3110

17.2 (6.5) 0.73 (0.29) 0.16 (0.19) 16.9 (4.2) 0.73 (0.25) 0.09 (0.12) 17.7 (4.0) 0.68 (0.25) 0.16 (0.20)

19.1 (7.5) 0.73 (0.31) 0.19 (0.20) 13.0 (0) 0.85 (0.07) 0.10 (0.14) 16.2 (3.0) 0.9 (0) 0.23 (0.25) 18.5 (4.9) 0.55 (0.32) 0.17 (0.20) 16.1 (4.2) 0.48 (0.25) 0.10 (0.13) 14.2 (2.7) 0.36 (0.21) 0.06 (0.10)

SD = standard deviation; POAG = primary open-angle glaucoma; OH = ocular hypertensmn; IOP = Intraocular pressure; PACG = primary angle- closure glaucoma.

* Presumed OH Includes those people with normal pressures and no other signs of glaucoma but who reported past treatment for glaucoma.

736

Wensor et al - Prevalence of Glaucoma in the Melbourne VIP

No.

700

600

500

400

ofeyes

300

t

Figure 2. Dlstnbutmn of cup/ disc ratios for the right and left eves.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

C/D ratio

higher rates of primary angle-closure glaucoma have been predominantly Asian populations3,” (neither of our two patients with angle closure glaucoma was of Asian de- scent).

Primary open-angle glaucoma increases significantly in prevalence with increasing age, and this also corre- sponds to other studies.3-14 The rate of definite POAG increases from 0.1% in the 40- to 49-year-old age group to 11.8% in the 90-year-old and older group. The raw data from the nursing home group also show glaucoma to be more prevalent in the older age groups having a mean age of 82.2 with a POAG rate of 6.7% as compared to the residential group, which had a mean age of 58.7 and an overall rate of 1.7%. However, the age-adjusted rates show the nursing home rates to be not significantly higher. Only one person in the residential population was considered to be blind because of glaucoma compared to one third of nursing home residents with glaucoma, although this visual impairment may have been the reason why they were admitted to the nursing home initially. The testing procedure was not as sensitive for the nursing home residents because of the inherent difficulty of as- sessing the elderly and institutionalized, and some cases

may have been missed, especially those with early visual field defects. It may be that glaucoma is less frequent in persons of this age because they belong to a “hardier” group who actually have survived to this age, and those more likely to get the disease are those who have not survived. Opinions differ as to the link between glaucoma and survival rate.21’22 In addition, as expected, there was a disproportionate number of females to males in the nursing homes (354:93), and it has been suggested that males are more susceptible to POAG glaucoma than are females,11.‘3 although our results, along with others,4,7S9 do not support this.

It also has been suggested that women are at a higher risk of having primary angle-closure glaucoma develop than males.3 We only found two persons with primary angle-closure glaucoma, clearly not enough to draw any similar conclusions, but both were females.

Only SO% of those who had definite glaucoma were diagnosed previously. This is highly consistent with rates reported in other studies worldwide,3X6,8,9X23,24 a worrying figure, especially because early detection of glaucoma is believed to be important for effective prevention of visual loss.

Table 5. Crude and Age-standardized Rates (%) of Glaucoma Using the Direct Method

Crude rates Adlusted rates

Males VIP (95% CL)

1.7 (0.9, 2.6) 1.7 (1.0, 2.3)

Expected Glaucoma Cases Nursing

Females VIP Total VIP Home Total* (95% CL) (95% CL) (95% CL)

1.6 (1.2, 2.2) 1.7 (1.2, 2.2) 6.7 (4.2, 9.2) 1.7 (1.1, 2.3) 1.7 (1.21, 2.21) 2.36 (0, 4.88)

VIP = Visual Impairment Project; CL = confidence limits.

* Diagnosed without consensus meeting or definitive visual field.

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Ophthalmology Volume 105, Number 4, April 1998

Table 6. The Prevalence of Primary Open-angle Glaucoma as Reported in Other Prevalence Studies

Study Location Age Group (yrs) Response (%) Prevalence (%) 95% CL

Sweden5 Ireland” Beaver Dam’ B&mwres~* Wales” South Afrxa’” Rotterdam” Casteldaccla’+ Barbados” Blue Mountams”~* Melbourne (d&me only) Melbourne (definite and probable

glaucoma)

CL = confidence Imnts; NA = not appkahle. * Defnute and probable glaucoma cases comhmed

55-69 77 0.93 NA 50+ 99.5 1.7 1.1, 2.2

43-84 83.1 2.1 NA 40+ 79.2 3.0 NA

40-75 91.9 04 NA 40+ 82.7 1.5 NA 55+ 80.0 1.0 0.63, 1.26 40+ 67.3 1.2 NA

40-84 83.5 6.1 5.6, 7.0 49+ 87.9 3.0 2.5, 3.6

40-98 83 1.7 1.21, 2.21

40-98 83 2.2 1.58, 2.83

The distributions of IOPs and C/D ratios highlight the fact that, although essential to diagnose glaucoma when used in conjunction with each other and visual field re- sults, each of these measures alone is not a good indicator of the disease. Apart from those with ocular hypertension, more than a third of those diagnosed with definite glau- coma had normal pressures and reported no current or prior treatment to lower their IOP. This figure is even higher in some other studies, such as the Blue Mountains24 and Baltimore25 eye studies, in which the figure is 74% and 55%, respectively. As for C/D ratios, a result of greater than 0.5 or a difference of 0.2 or greater between eyes may be regarded as suspicious,2” whereas our rates for these occurrences were approximately 13 and 9 times, respectively, more prevalent than our actual POAG rate. Even the number of persons with C/D ratios of greater than 0.7 was approximately four times the POAG glau- coma rate. Conversely, seven (13.2%) of those regarded as definite glaucoma sufferers had “normal” C/D ratios, that is, less than or equal to 0.3.

The Melbourne VIP has the advantage of being a large population-based prevalence study with a standardized protocol and included institutionalized residents. Its main disadvantage, as mentioned earlier, was that the nursing home data were not as accurate as or directly comparable to the residential data because of some variations in the protocol due to the difficulty in examining institutional- ized persons, particularly performing fundus photography and visual field testing, and the difficult working condi- tions associated with conducting ophthalmic testing in nursing homes.

In conclusion, glaucoma in Melbourne has been shown to be a significant cause of eye health problems. As with other areas with a similar ethnic make-up,‘,‘,“,‘.” POAG is by far the most common of the glaucoma types in Melbourne. Glaucoma becomes steadily more prevalent with increasing age, an important fact to consider with the current trend of an aging population.

Acknowledgments. The authors thank Carl Zeiss Pty Ltd. for their donation of the visual field analyzer, automatic refrac-

738

tor, and lens analyzer. The authors also thank Cara Jin, Sharon Lee, Marie Bissinella, Caroline De Paola, Juanita Kidd, Charles Guest, Sharon Bailey, Cathy Walker, Claire McKean, Dr. Julian Rait, Professor Paul Mitchell, Dr. Ivan Goldberg, Dr. Laurie Hirst, and Dr. Paul Healy.

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