Two questions asked most frequently by readers about age-related macular degeneration (AMD) involve (a) individual risk for the disorder and (b) the likelihood of eventual involvement of both eyes. In response, several recent studies have attempted to address these critically important questions:
- Data from the ongoing Blue Mountains Eye Study (BMES) and the Age-Related Eye Disease Study (AREDS) identified a number of demographic and eye-related factors that were used to develop a “scoring system” to predict the risk of developing AMD up to 10 years in the future. You can read more about this research at Is It Possible to Predict Risk for Developing Macular Degeneration? on the VisionAware blog.
- Data from the ongoing Beaver Dam Eye Study investigated the pattern and progression of wet (also called neovascular) AMD and determined that having wet AMD in one eye was associated with an increased incidence and progression of AMD in the other eye. You can read more about this research at Macular Degeneration in One Eye Associated with Increased Incidence and Progression in the Other Eye on the VisionAware blog.
Now, an international group of researchers from the three-continent AMD Consortium have combined data from the Blue Mountains Eye Study, the Beaver Dam Eye Study, and the Rotterdam Study (all explained below) and concluded that “one in four to one in five unilateral [i.e., occurring in one eye] any stage [i.e., early through late] of AMD cases, and up to one in two unilateral late AMD cases, progressed to bilateral [i.e., both eyes] in 5 years. Known AMD risk factors, including smoking, are significantly associated with the progression to bilateral involvement.”
From the British Journal of Ophthalmology
This new macular degeneration research, titled Five-year progression of unilateral age-related macular degeneration to bilateral involvement: the Three Continent AMD Consortium report, has been published “online first” in the January 2017 edition of the British Journal of Ophthalmology (BJO). BJO is an international peer-reviewed journal for ophthalmologists and visual science specialists that publishes clinical investigations, clinical observations, and clinically relevant laboratory investigations related to ophthalmology.
The authors are members of the AMD Consortium (with all authors listed online) and represent the following countries and institutions: University of Sydney; University of Newcastle; John Hunter Hospital and Hunter Medical Research Institute, Australia; Erasmus Medical Center, Rotterdam; Royal Netherlands Academy of Arts and Sciences, Leiden; Netherlands Genomics Initiative, The Hague; Radboud University Nijmegen Medical Center, The Netherlands; Case Western Reserve University, Cleveland, Ohio; University of Wisconsin School of Medicine and Public Health, United States.
More about Age-Related Macular Degeneration
Age-related macular degeneration (AMD) is a gradual, progressive, painless deterioration of the macula, the small sensitive area in the center of the retina that provides clear central vision. Damage to the macula impairs the central (or “detail”) vision that helps with essential everyday activities, such as reading and writing, preparing meals, watching television, and personal self-care.
AMD is the leading cause of vision loss for people aged 60 and older in the United States. According to the American Academy of Ophthalmology, 10-15 million individuals have AMD and about 10% of people who are affected have the “wet” type of AMD.
Wet (Neovascular) Macular Degeneration
In wet, or exudative, macular degeneration (AMD), the choroid (a part of the eye containing blood vessels that nourish the retina) begins to sprout abnormal new blood vessels that develop into a cluster under the macula, called choroidal neovascularization (neo = new; vascular = blood vessels).
Because these new blood vessels are abnormal, they tend to break, bleed, and leak fluid under the macula, causing it to lift up and pull away from its base. This damages the fragile photoreceptor cells, which sense and receive light, resulting in a rapid and severe loss of central vision.
Dry Macular Degeneration
The dry (also called atrophic) type of AMD affects approximately 80-90% of individuals with AMD. Its cause is unknown, it tends to progress more slowly than the wet type, and there is not – as of yet – an approved treatment or cure.
“Atrophy” refers to the degeneration of cells in a portion of the body; in this case, the cell degeneration occurs in the retina.
In dry age-related macular degeneration, small white or yellowish deposits, called drusen, form on the retina, in the macula, causing it to deteriorate or degenerate over time.
Drusen are the hallmark of dry AMD. These small yellow deposits beneath the retina are a buildup of waste materials, composed of cholesterol, protein, and fats. Typically, when drusen first form, they do not cause vision loss. However, they are a risk factor for progressing to vision loss.
Risk Factors for Macular Degeneration
The primary risk factors for AMD include the following:
- Smoking: Current smokers have a 2-3 times higher risk for developing AMD than do people who never smoked. It’s best to avoid second-hand smoke as well.
- Sunlight: Ultraviolet (UV) light is not visible to the human eye, but can damage the lens and retina. Blue light waves that make the sky, or any object, appear blue, are visible to the human eye and can also damage the lens and retina. Avoid UV light and blue/violet light as much as possible by wearing sunglasses with an amber, brown, or orange tint that blocks both blue and UV light.
- Uncontrolled hypertension: The National Eye Institute (NEI) reports that persons with hypertension were 1.5 times more likely to develop wet macular degeneration than persons without hypertension. It’s important to keep your blood pressure controlled within normal limits.
- A diet high in packaged, processed food and low in fresh vegetables: NEI suggests that eating antioxidant-rich foods, such as fresh fruits and dark green leafy vegetables (kale, collard greens, and spinach) may delay the onset or reduce the severity of AMD. Eating at least one serving of fatty fish (salmon, tuna, or trout) per week may also delay the onset or reduce the severity of AMD.
- Race: According to NEI, Whites/Caucasians are more likely to have AMD than people of African descent.
- Family history: NEI reports that individuals with a parent or sibling with AMD have a 3-4 times higher risk of developing AMD.
You can read more about the full range of AMD risk factors at Risk Factors for Age-Related Macular Degeneration on the VisionAware website.
What is the Blue Mountains Eye Study?
The longitudinal Blue Mountains Eye Study (BMES), named after the Australian mountain range, is the first large population-based assessment of visual impairment and common eye diseases of a representative sample of older Australians. A longitudinal study follows, and gathers information about, the same individuals or group of people over an extended period of time – often many decades.
The ongoing BMES began in 1992-1993, with the recruitment of 3,654 people aged 50 and older. Follow-up exams were conducted in 1997-1999 (5-year), 2002 (10-year) and 2007-2009 (15-year). You can read more about the BMES at Research Data Australia.
What is the Beaver Dam Eye Study?
The longitudinal Beaver Dam Eye Study is funded by the National Eye Institute. The purpose of the Study is to collect information on the prevalence and incidence of age-related cataract, macular degeneration, and diabetic retinopathy. The study was designed to discover, or detect, causes of these conditions.
The study was funded initially in 1987. A private census conducted in the city and township of Beaver Dam, Wisconsin found that there were approximately 6,000 people aged 43 through 84 years. Approximately 5,000 of them participated in the baseline examination between 1988 and 1990.
Five-, 10-, 15-, and 20-year follow-up examinations have taken place and 3,700; 2,800; 2,100; 2,000; and 1,900 people participated in each of the respective examination phases. Thus far, there have been more than 300 publications describing the prevalence and incidence of visual loss, age-related macular degeneration, cataract, and associated risk factors as a result of this study. You can read more about the study at the Beaver Dam Eye Study website.
What is the Rotterdam Study?
The Rotterdam Elderly Study is a longitudinal study in the Ommoord district in Rotterdam, the Netherlands. Following the pilot study in 1989, recruitment began in January 1990. The main objectives of the Rotterdam Study are to investigate the risk factors of cardiovascular, neurological, ophthalmological, and endocrine diseases in older persons. The study has recruited approximately 15,000 subjects aged 45 years or older.
Participants were interviewed at home and received an extensive set of examinations, repeated every 3-4 years. They were followed for the most common diseases in older persons, including coronary heart disease, heart failure, and stroke; Parkinson’s disease; Alzheimer’s disease and other dementias; depression and anxiety disorders; macular degeneration; glaucoma; diabetes; and osteoporosis. You can read more about the study at the University Medical Center Rotterdam website.
What the Macular Degeneration Progression Study Found
Excerpted from the study abstract:
Purpose: To assess the 5-year progression from unilateral [i.e., in one eye] to bilateral [i.e., in both eyes] age-related macular degeneration (AMD) and associated risk factors.
Design: Pooled data analyses of three prospective population-based cohorts, the Blue Mountains Eye Study, Beaver Dam Eye Study and Rotterdam Study.
Methods: Retinal photography and interview with comprehensive questionnaires were conducted at each visit of three studies. AMD was assessed following the modified Wisconsin AMD grading protocol. Progression to bilateral any (early and late) or late AMD was assessed among participants with unilateral involvement only.
Results: In any 5-year duration, 19–28% of unilateral any [i.e., early through late] AMD cases became bilateral and 27–68% of unilateral late AMD became bilateral. Factors associated with the progression to bilateral involvement of any AMD were age, carrying risk forms of the complement factor H (CFH) and age-related maculopathy susceptibility 2 (ARMS2) genes, smoking, and the presence of large drusen area or retinal pigmentary abnormalities in the first eye.
[Editor’s note: The CFH gene makes a protein called complement factor H (CFH), which regulates a part of the body’s immune response known as the complement system. It destroys bacteria and viruses, triggers an inflammatory response, and removes debris from cells and tissues. CFH protects healthy cells by preventing the complement system from being activated when it is not needed. (Source: Genetics Home Reference.)]
[The ARMS2 gene provides instructions for making a protein whose function is unknown. Studies suggest that the ARMS2 protein is found primarily in the placenta and in the retina. However, it is unclear what role, if any, the protein plays in early development or normal vision. (Source: Genetics Home Reference.)]
Conclusion: One in four to one in five unilateral any [i.e., early through late] AMD cases, and up to one in two unilateral late AMD cases, progressed to bilateral in 5 years. Known AMD risk factors, including smoking, are significantly associated with the progression to bilateral involvement.