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[Blue Mountains Eye Study]
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Blue Mountains Eye Study

The Blue Mountains Eye Study (BMES) was the first large population-based assessment of visual impairment and common eye diseases of a representative older Australian community sample. The project was conducted in an area that included Katoomba, Leura, Medlow Bath (postcode 2780) and Wentworth Falls (postcode 2782). This area was chosen as its demography is similar to the overall Australian population of this age.

The Population
The Examinations
The Findings

The Population

In late 1992 the target population was identified by a door-to-door census of all dwellings in the two postcode areas. 3,654 residents aged 49-97 were examined during the period 1992-1994 (an overall response of 82.4% of non-institutionalised residents - BMES-1)

During 1997-1999, all surviving participants were invited to attend a 5-year follow up examination, for which 2,334 persons returned (75% of survivors - BMES-2).

A second census of the same postcode areas was conducted in 1999, identifying a further 1,510 residents now eligible to participte of which 1,206 were examined as part of an extension study during 1999-2000 (BMES-E).

In 2002, participants were invited to return for 10-year follow-up exams, and during 2002-2004 1952 original participants were re-examined (BMES-3)

15-year follow-up exams were conducted from 2007-2009 (BMES-4).


The Examinations

At each examination, a detailed assessment of eye disease and other general health measures was conducted. Participants were also asked to attend fasting blood tests after each examination and complete a detailed questionnaire about the types of food they consumed. At the 5 and 10 year exams, a test of memory and cognition (Mini Mental State Examination), questions about quality of life (Short Form 36) and visual functioning were also conducted.

Eye conditions were assessed at each examination by taking a series of photographs of the eye. Photographs of the retina (the back of the eye) were used to assess the presence of diseases like macular degeneration or diabetic eye damage. Stereo photographs of the optic nerve (which enters at the back of the optic disc) were taken to assess changes that, together with an automated test of the field of vision, indicate the presence of glaucoma. Two types of photographs were taken of the lens inside the eye to grade the presence of the different types of cataract. All of these photographs are graded using standard protocols (developed for the Beaver Dam Eye Study in Wisconsin, USA).

Participants at 5 and 10 years were also asked to attend a detailed hearing assessment (BMHS). The hearing tests were conducted in sound booths by audiologists.


The Findings

Visual impairment
BMES findings indicated that under- or uncorrected refraction is frequent, with vision improving by one line on the vision chart in 45% of participants after a careful refraction and by three or more lines in 13%. The frequency of bilateral and unilateral visual impairment, after refraction, increased from 0.6% and 3.6%, respectively, for people aged less than 60 to rates of 26.3% and 52.2%, respectively, for people aged 80 years or older. After taking into account the effect of age, visual impairment was significantly more frequent in women than men. At each age, women were less likely to achieve 6/6 or 'normal' corrected vision than men. Overwhelmingly, age-related maculopathy was the predominant cause of blindness in both eyes (all ages over 50), and of moderate impairment affecting both eyes of persons aged 70 or older. However, cataract was the most common cause of mild visual impairment affecting both eyes. Visual impairment affecting only one eye was caused most frequently by amblyopia (poor vision from childhood) in those under age 60, while in older ages was due to cataract when mild and was caused jointly by age-related maculopathy and cataract when moderate or severe.

Both impaired vision and reduced visual field were found to double the risk of falls. For those aged 75 or older, moderate visual impairment was associated with a nine-fold increase in risk of hip fracture during the subsequent two years. People with any visual impairment were three times as likely to use community support services, including 'meals-on-wheels', home care or home nursing care, and were six times as likely to state that they felt unable to go out alone. They were also more likely to rank their general health as poorer. Self-reported car accidents as driver were also twice as high among those with visual impairment compared to those without. After taking into account a range of factors predicting placement, older people with visual impairment were significantly more likely to be admitted permanently to a nursing home. We previously found a high rate of visual impairment and a ten-fold higher rate of blindness among nursing home residents in this region than in the community. After adjusting for age and all of the factors found associated with mortality, those who were visually impaired had an 80% higher risk of dying than people with good vision. The mechanism of this impact is not known but it could act via depression.

BMES reports identified different sets of risk factors for each of the three principal types of cataract. For nuclear cataract, both smoking and heavy alcohol intake were associated with an increased risk, while higher dietary intakes of protein, vitamin A, thiamine, niacin and riboflavin were protective. Cortical cataract was more frequent in women at all ages, and had a vascular profile of associations. The presence of diabetes, vascular disease and elevated plasma fibrinogen increased the risk, while alcohol intake, higher dietary polyunsaturates and use of post-menopausal hormonal therapy by women, were protective. A dose- and duration-related increase in the prevalence of posterior subcapsular cataract was associated with the use of inhaled steroids. Sunlight exposure or sunlight-related eye lesions, smoking, diabetes, myopia, dark iris colour, higher dietary salt, and elevated plasma fibrinogen levels were all associated with a higher risk of posterior subcapsular cataract.

Age-related maculopathy (macular degeneration)
BMES data suggested an exponential increase in the frequency of late-stage macular degeneration with increasing age and somewhat higher rates in women than in men. Pooled prevalence data from the Blue Mountains, Beaver Dam (USA) and Rotterdam studies found that compared with the frequency in people aged 55-69 years, signs of late age-related macular degeneration were six times more frequent among those aged in their seventies and 25 times higher in those aged 80 years or older. The BMES 5-year incidence rate of 1.1% for new late lesions and new early-stage age-related maculopathy (7.7%) was very close to comparable rates (0.9%, 8.2%) from the Beaver Dam Study, using the same definition.

Other than age, several groups of factors appear to either increase or decrease the risk of age-related maculopathy, including smoking, vascular, familial, racial or ethnic, nutritional, hormonal, ocular or sunlight-related factors. The BMES confirmed the highest risk of late-stage macular degeneration among current smokers, who had a four-fold increased risk compared with past or non-smokers, including a smoking exposure gradient. Using population attributable risk calculations, we estimated that smoking may thus substantially contribute to around 20% of blindness in Australians aged over 50. This finding has been confirmed internationally, with the smoking relationship strongly confirmed in the pooled three-continent data. Our 5-year incidence data demonstrated associations between current smoking at baseline and new late lesions. Importantly, we also showed that smokers developed late-stage macular degeneration an average 10 years before nonsmokers. We plan to pool age-related maculopathy incidence data from the Beaver Dam and Rotterdam studies to improve study power. Interestingly, we found no micronutrient associations with age-related maculopathy, but we did observe a significant protective association from higher fish consumption and an increased risk associated with higher consumption of dietary fat.

The BMES found that only half of the cases with signs of glaucoma had previously been diagnosed. The study also confirmed many risk factors for the disease; the strongest was increasing age, which had an exponential relationship. Having a family history of glaucoma affecting parents or siblings increased the risk three-fold. A number of glaucoma genes have now been identified. Other systemic factors included diabetes (two times risk) and high blood pressure (70% increasing risk). In people with a family history of glaucoma, use of inhaled steroid medications was associated with glaucoma or elevated eye pressure in a dose-related manner. Important eye signs found to increase the risk of finding glaucoma included elevated eye pressure (five-fold risk), myopia or short-sightedness (two-fold risk), asymmetry between the two optic nerves, an appearance of atrophy around the nerve, fine splinter haemorrhages at the edge of the optic nerve or fine dandruff deposits on the capsule of the lens.

Diabetic and other vascular retinopathy
In the BMES population, a history of diabetes was given by 5.9% and elevated fasting blood glucose diagnosed diabetes in a further 2.2% of subjects seen. Diabetes was associated with higher rates of obesity, high blood pressure (hypertension) and abnormal blood fats (higher triglycerides and lower levels of the protective "HDL"-cholesterol), as well as vascular disease, gout and thyroid disease.

Diabetic eye damage (retinopathy) was present in one third of those with diabetes, including 16% of those with previously undiagnosed diabetes. The presence of diabetic retinopathy was related to higher levels of blood glucose in this population. People with diabetes had significantly worse vision that those without this condition. The cumulative 5-year incidence of diabetic retinopathy was 22.2%. Progression of retinopathy by one step on the standard scale was found in one in four of those with retinopathy at baseline.

Isolated retinopathy lesions (microaneurysms, haemorrhages) were also found in 9.8% of subjects without a history or blood test findings suggesting diabetes. This rate was higher than in some earlier studies. The finding of retinopathy was strongly related to hypertension in a dose-dependent manner, as well as to other vascular risk factors. A number of other retinal vascular signs (focal narrowing and an opaque appearance of the small retinal arterioles, nipping of the retinal veins and signs of small cholesterol crystals in the lumen of branch retinal arterioles were identified. All of these signs were shown to predict stroke or cerebrovascular death during the 5-year follow-up, independently of age and sex, as well as measures of hypertension and smoking.

Hearing Loss
Impaired hearing is one of the most frequently reported disabilities in Australia and represents an important area of public health concern because of the under-utilisation of hearing aids and other rehabilitation measures. Hearing was assessed in people after they attended the 5-year eye examinations during 1998-2000. We defined hearing loss as the average of hearing thresholds measured over four frequencies in both ears greater than 25 decibels. This level of hearing impairment was present in 39% of those aged 55 or older. The frequency of hearing loss almost doubled for each decade of age - from 10.5% of those aged less than 60 years rising to 77.7% of those aged 80 or older - and was significantly more frequent in men (44.2%) than in women (35.7%). Most cases (26%) were mild, but 11% had moderate, 2% had marked and 0.5% had profound hearing loss in both ears. Overall, less than half of those with measured hearing loss had sought help and less than one third used a hearing aid. Many factors were found associated with hearing loss in a multi-variable model that included age (14% per year); male gender (30% increased risk), diabetes (a 50% increased risk with a strong duration-relationship), a history of work in a noisy industry (70% increased risk), lower educational attainment (25% increased risk) and being a current smoker (50% increased risk). People with impaired vision were more likely to also have hearing loss.




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