Risks for major eye diseases increased by obesity

Millions of obese Americans are at increased risk of AMD, cataract, retinopathy and glaucoma.

Obesity and overweight have reached what may be called epidemic proportions in the United States. Nearly two-thirds of U.S adults are overweight, and nearly a third are obese, according to data gathered by government researchers in 1999 and 2000. The prevalence of obesity has doubled since 1960, most of that increase coming in the past 20 years.

The effects of obesity and overweight on systemic health are well known to physicians. A report from the Centers for Disease Control in March indicated that obesity is catching up to smoking as the No. 1 cause of death in the United States. Diet and physical inactivity caused 400,000 deaths, or 16.6% of total deaths, in 2000, up from 300,000, or 14% of deaths, in 1990, according to the CDC report.

Almost 130 million adult Americans are overweight or obese — about 64% of the population — putting them at increased risk for cardiovascular disease, diabetes, some types of cancer and some forms of disability, according to the CDC.

“Americans need to understand that overweight and obesity are literally killing us,” said Health and Human Services Secretary Tommy Thompson at a news conference announcing the release of the CDC report.

But less well known to physicians and the general public are the effects of overweight and obesity on the eye. Recent research shows that obesity puts people at increased risk for at least four major, blinding eye diseases. The risks of age-related macular degeneration, diabetic retinopathy, cataract and glaucoma can be increased in individuals either through the presence of obesity-related systemic diseases such as diabetes or directly due to a high body mass index (BMI), abdominal circumference or waist-hip ratio, research has shown.

Johanna M. Seddon, MD, ScM, a surgeon in ophthalmology and director of the Epidemiology Unit, Massachusetts Eye and Ear Infirmary, Harvard Medical School, has spent 2 decades researching the relationships between nutrients and eye health, particularly AMD. According to Dr. Seddon, “There is a direct link between obesity and eye health. Obesity is associated with decreased carotenoid intake. It seems that people who are consuming less of the healthy types of foods are the heavier people. There’s a relationship between increased lutein in the diet and decrease in AMD. People aren’t getting enough of the nutrients they need, and so it’s causing damage to the eye.”

Dr. Seddon said counseling patients on the effects of obesity is part of the ophthalmologist’s duty.

“It is the ophthalmologist’s responsibility to discuss these risks with their patients,” Dr. Seddon said. “It shouldn’t be left up to the primary care physician — pick up the ball and note these modifiable factors to your patients at risk, especially those with a family history of AMD. Don’t smoke, watch your blood pressure and cholesterol.”

This article reviews some of the research – beginning with Dr. Seddon’s work in AMD – that links obesity to diseases of the eye. Other articles in this Population at Risk discuss counseling and caring for overweight and obese patients and the international implications of the overweight epidemic.

AMD

Obesity’s direct effect on eye health was not well recognized until recently. In 2003, Dr. Seddon found links between increased BMI (a person’s total weight in kilograms divided by the square of height in meters), waist circumference, waist-hip ratio and AMD progression.

In a study published in Archives of Ophthalmology, 261 middle-age and elderly patients were found to have a correlation between high levels of body fat and AMD progression.

“Patients with a BMI between 25 to 30 kg/m² or greater were more than twice as likely to experience AMD progression compared to patients with a BMI less than 25 kg/m²,” Dr. Seddon said.

A larger waist circumference was associated with a two-fold risk of disease progression, having a more significant risk the greater the waist circumference (P = .02). Patients with a higher waist-hip ratio also increased their risk of disease progression (P = .02).

“To my knowledge this is the first time that anyone has shown a relationship between abdominal obesity and overall obesity to AMD progression,” Dr. Seddon said.

Researchers found that increased physical activity in the cohort studied led to a decrease in progression to AMD. Considering these factors, Dr. Seddon discussed a possible association between cardiovascular disease and AMD.

“This evidence points to the growing knowledge of the similarities between heart disease and AMD,” Dr. Seddon said. She speculated that cardiovascular factors are somehow related to the neovascularization process that occurs in AMD. “It points to some vascular etiology,” she said.

Cataract

A study in Ophthalmic Epidemiology also found an association between cardiovascular disease and eye disease.

Christine Younan, MD, of the University of Sydney, and researchers at the Save Sight Institute in Sydney found a link between cardiovascular disorders and cataract in the Blue Mountain Eye Study.

In the study, 2,300 patients over age 48 were followed for 5 years. Patients answered vascular history questionnaires and were measured for height, weight and blood pressure. Complete ophthalmic examinations were also performed. Photographs of the lens were taken at initial visits and then again 5 years later to grade for presence of cortical, nuclear, posterior or subcapsular cataract.

Outcomes showed that obesity was significantly associated with the incidence of cortical and posterior subcapsular cataract. Patients over age 65 who were treated for hypertension had a higher incidence of posterior subcapsular cataract at baseline than patients with normal blood pressure. A higher incidence of cataract surgery was found in patients with a history of angina and heart-related problems.

“These longitudinal data provide some evidence supporting a relationship between cardiovascular disease, vascular risk factors and incident cataract and cataract surgery,” the authors said in the study abstract.

Retinopathy

Evidence has also been found to link retinopathy to vascular disorders and type 2 diabetes, a disease often triggered by obesity.

In a study in Diabetes Care in 2002, Hendrik A. van Leiden, MD, and researchers at the University Medical Center in Amsterdam, Netherlands, found the incidence of retinopathy to be positively associated with increased BMI, among other factors.

“Retinopathy is a multi-factorial microvascular complication, which, apart from hyperglycemia, is associated with blood pressure, lipid concentrations and BMI,” the authors said in the study abstract.

As part of the Hoorn Study, a population-based study of more than 2,484 50- to 70-year-old white subjects, a subset of 626 diabetic and non-diabetic patients was selected for investigation.

Patients underwent ophthalmic and fundus examinations to assess the incidence of retinopathy.

Retinopathy was positively associated with elevated blood pressure, BMI, cholesterol and triglyceride serum levels. Researchers noted that elevated blood pressure, plasma totals and high cholesterol levels were associated with the presence of retinal hard exudates.

The risk of retinopathy was also linked to an increased waist-hip ratio in another part of the Hoorn Study carried out by Dr. van Leiden. The study, published in Archives of Ophthalmology in February 2003, followed 233 patients for 9.5 years to investigate the effect of sex, age, glycosylated hemoglobin, hypertension, BMI, waist-hip ratio, serum lipid levels and smoking on the incidence of retinopathy in persons with normal and abnormal glucose metabolism.

Abdominal obesity (waist-hip ratio), glycemia and hypertension were strong determinants for retinopathy development. No significant associations between retinopathy and the remaining risk factors were found in this study.

Elevated IOP, glaucoma

Elevated IOP and glaucoma are also associated with obesity and vascular disease. Two studies from Asia have established a correlation between increased BMI and elevated IOP.

In a study led by Keiko Mori, PhD, at the University of Nagoya, Japan, researchers conducted a cross-sectional analysis on 25,296 Japanese men and women. The study appeared in the International Journal of Epidemiology in 2000.

Patients were measured multiple times during a 10-year period for IOP, blood pressure and weight. Mean IOP measurements at baseline were 11.6 mm Hg. After controlling for age, sex and blood pressure, researchers found a significant association between longitudinal change in IOP and change in weight.

“These findings suggest that obesity is an independent risk factor for increase in IOP,” the study authors concluded.

An article in the Korean Journal of Ophthalmology found a similar link between obesity and elevated IOP in a large Asian population.

Jong-Soo Lee, MD, PhD, and researchers at the College of Medicine at Pusan National University in Korea, compared the incidence of elevated IOP in patients who were systolic or diastolic hypertensive and obese (group 1) and patients who were systolic or diastolic hypotensive and lean (group 2).

“IOP increased significantly with increasing systolic blood pressure, diastolic blood pressure and obesity index (P < .05),” the study authors said.

The mean IOP of group 1 was higher than that of group 2. The difference in IOP was statistically significant (P < .05).

Researchers said that this data could aid investigations on the epidemological and etiological influences related to risk factors of glaucoma, specifically in Asian populations.

For Your Information:

• Johanna M. Seddon, MD, ScM, a surgeon in ophthalmology and director of the Epidemiology Unit, Massachusetts Eye and Ear Infirmary, Harvard Medical School, can be reached at Massachusetts Eye and Ear Infirmary, 243 Charles St., Boston, MA 02114; 617-573-4010; fax: 617-573-3570; e-mail: johanna_seddon@meei.harvard.edu.

References:

• Seddon JM, Cote, J, Davis N, et al. Progression of age-related macular degeneration: association with body mass index, waist circumference, and waist-hip ratio, Arch Ophthal. 2003;121(6):785-792.
• Younan C, Mitchell P, Cumming R, et al. Cardiovascular disease, vascular risk factors and the incidence of cataract and cataract surgery: the Blue Mountains Eye Study. Ophthalmic Epidemiol. 2003;10(4):227-240.
• Van Leiden HA, Dekker JM, Moll AC, et al. Blood pressure, lipids, and obesity are associated with retinopathy: the Hoorn Study. Diabetes Care. 2002;25(8):1320-1325.
• Van Leiden HA, Dekker JM, Moll AC, et al. Risk factors for incident retinopathy in a diabetic and nondiabetic population: the Hoorn Study. Arch Ophthal. 2003;121(2):245-251.
• Mori K, Ando F, Nomura H, et al. Relationship between intraocular pressure and obesity in Japan. Int J Epidemiol. 2000;29:661-666.
• Lee JS, Choi YR, Lee JE, et al. Relationship between intraocular pressure and systemic health parameters in the Korean population. Korean J Ophthalmol. 2002;16(1):13-19.