Study provides data on glaucoma incidence, progression

Fort Lauderdale, FL-The Blue Mountains Eye Study has yielded 10-year data on the incidence and progression of glaucoma in an elderly population as well as valuable information on systemic and ocular predictors.

While shedding light on the particular population group under study in an Australian community, the data also will be useful in other respects, such as comparing this population with others and validating glaucoma risk calculators, said Paul Mitchell, MD, PhD, FRACS, FRANZCO, FRCOphth, FAFPHM, professor, Westmead Hospital, the University of Sydney, Australia.

Age is risk factor

The Blue Mountains Eye Study is a population-based cohort study conducted to determine the prevalence of open-angle glaucoma and ocular hypertension in an Australian community whose residents are 49 years of age or older.

There were 3,654 persons included in the study at baseline, representing 82% of those eligible from an area west of Sydney; baseline examinations were conducted between 1992 and 1994. At 5 years, 2,334 persons (75% of survivors) were examined, and at 10 years, 1,953 (76% of survivors). Data were available on 2,461 participants from the second or third examinations.

At all three examinations, glaucoma was diagnosed from the presence of matching optic disc cupping with neuroretinal rim thinning (graded from stereophotographs) plus glaucomatous visual field defects (assessed from Humphrey 30-2 fields) after gonioscopy. Open-angle glaucoma (OAG) was diagnosed when glaucomatous defects on the 30-2 test matched the optic disc changes, without regard to the IOP level.

The overall prevalence of OAG at baseline was 3%; 2.4% of cases (87 persons) were considered to have definite OAG, and 0.6% (21 persons) were categorized as having probable OAG. Some participants whose disease was labeled probable had incomplete data.

Other findings showed that glaucoma incidence was higher in women (5.6%) than in men (3.0%) and that it increased markedly by age, after adjusting for sex. The incidence levels were 2.0%, 3.7%, and 10.3%, respectively, for persons aged less than 60 years, 60 to 69 years, and 70 or more years at baseline.

Discussing the 10-year data from a series of exams that began in 2002, Dr. Mitchell reported that 53.4% of the original cohort had been retained. The cumulative 5-year incidence of OAG was 1%, and the cumulative 10-year incidence was 2% to 10%, depending on the age cohort. Many of the original 108 participants with definite or probable glaucoma diagnosed were very old at baseline and did not survive to the 5-year or 10-year exams.

Less than one-third of the participants with glaucoma had previously had ocular hypertension diagnosed. The rate of progression among patients with ocular hypertension was about 20%, which is higher than reported in the Ocular Hypertension Treatment Study because of different study criteria, Dr. Mitchell said. In the Blue Mountains Study, the overall risk of progression among patients with ocular hypertension was increased by about eightfold.

Systemic factors that have been found to increase the risk of glaucoma in this population included diabetes and high blood pressure. Poorly controlled hypertension, in particular, seemed to be linked to a modest level of increased risk of OAG. This risk was independent of the effect of hypertension on IOP and other glaucoma risk factors. Systemic hypertension was present in 45.7% of subjects, OAG in 3.0%, and ocular hypertension in 5.2%.

Analysis has also shown that systemic hypertension was associated with ocular hypertension, a relationship that may be due to the influence of blood pressure on IOP, Dr. Mitchell said.

Significant baseline predictors of incident glaucoma determined from age- and sex-adjusted and multivariate models included age, female gender, family history, blood pressure, ocular hypertension, the presence of beta-peripapillary atrophy, cup-disc ratio, disc hemorrhage, and reduced central corneal thickness.