Macular Degeneration types and risk factors

Age Related Macular degeneration (ARMD) is a disease that causes progressive damage to the macula. Macula

is the central part of the retina that allows us to see fine details. When the macula degenerates, people experience blurring or darkness in the center of their vision. Macular degeneration leads to loss of central vision needed for activities requiring fine vision such as reading, driving and recognising faces. The words on a page may look blurred, or straight lines may look distorted. Peripheral vision is usually retained in macular degeneration therefore blindness (inability to see all light) does not typically occur even in advanced/end-stage macular degeneration. However the central vision loss impairs proficiency in performing most activities of daily living and can make it more difficult for people to live independent lives.

There are two forms of macular degeneration

● Dry

(atrophic) macular degeneration

● Wet

(neovascular / exudative) macular degeneration

Dry macular degeneration is the more common form of the disease and accounts for 90% of all AMD. The classic lesion in dry macular degeneration is Geographic atrophy

. Geographic atrophy of the macula causes severe central visual loss. There is no treatment, laser or other, that can halt or reverse the relentless progression of dry macular degeneration related vision loss.

The precursor lesion that leads to the development of Geographic atrophy is a small yellowish macular lesion called 'drusen'. There are 2 types of drusen (soft and hard). Soft drusen

are pale yellow and large with ill defined margins. In persons over the age of 55 years, soft drusen, particularly those larger than 63 micrometer, are a sign of age-related maculopathy. (Sixty-three micrometers is approximately half the width of a major retinal vein at the optic nerve head). Hard drusen

(round, yellow with well-defined boundaries) are common in young people and are not considered to represent age-related maculopathy. It is the soft drusen, not the hard drusen, that evolves to macular degeneration.

Wet macular degeneration form is less common but more severe than the dry form. It accounts for approximately 10% of all AMD but 90% of all blindness from the disease. This form is characterized by choroidal neovasculariztion

(CNV), the development of abnormal blood vessels beneath the retinal pigment epithelium (RPE) layer of the retina. These vessels can bleed and eventually cause macular scarring which can result in profound loss of central vision (disciform scar

To summarize:

● Early age-related maculopathy lesion is a soft drusen.

● Late-stage macular degeneration lesion are 1). 'Geographic atrophy

' and 2). 'Neovascular

lesions' which include Choroidal neovascularization

and Disciform scar

Geographic atrophy represents 'dry' macular degeneration. Neovascular lesions represent 'wet'

macular degeneration.

Drusen evolve from hard to soft. They increase in number, size, and confluence to eventually evolve to dry or wet macular degeneration. If, in addition, pigment changes occur in the retina, the risk of developing dry or wet macular degeneration increases considerably.

In general, the risk of developing macular degeneration (dry or wet) is strongly dependent on the age and the stage of age-related maculopathy (i.e. whether you have soft drusen or pigment changes etc.). Therefore, a person who is 80 years or older and who has soft indistinct drusen and pigmentary changes has a very high risk of developing macular degeneration over the next 5 years. The 5-year risk of developing macular degeneration in such an individual is 42% (Arch Ophthalmol 2003;121:519-26).

As with macular degeneration, the risk of developing early maculopathy is also dependent on your age. If you have normal retina, then over the next 5 years the risk that you will develop retinal changes of early maculopathy is 0.7% if your age is less than 60 years, but the risk is 22.5% if you are more than 80 years of age.

If there is macular degeneration in one eye, then the fellow eye is at a high risk of developing macular degeneration as well. The risk of the fellow eye developing macular degeneration was reported to be 55% in the AREDS and 38.7% in the Rotterdam Study.

Comparing the data from different studies, it seems that the risk of developing macular degeneration is higher in the US as compared with the European population. There may be unknown genetic and environmental factors that play a role in producing this difference.

Strong Risk Factors

Possible Risk Factors

● Exposure to sunlight especially blue light

● Hypertension

● Cardiovascular Risk Factors - high cholesterol, obesity

● Female gender

● Non-hispanic Whites

● Hyperopia (far sightedness)

Human retina is protected from ultraviolet radiation by the cornea which absorbs below 295 nm and the lens which absorbs strongly below 400 nm. Therefore ultraviolet (UV) light exposure is not related with development of macular degeneration. Several studies have suggested that exposure to sunlight (i.e. "visible component" of light spectrum) may play a role in the development of macular degeneration, however the relationship between sunlight exposure and macular degeneration have also produced inconsistent results.

A recent study has shown that people who stay outdoors in the summer sun for more than 5 hours a day in both their teens and 30s have a twofold greater likelihood of developing early macular degeneration changes (soft drusen or increased retinal pigment). In these individuals i.e. those who have high sun exposure, the likelihood of developing early macular degeneration is considerably reduced by wearing hats or sunglasses at least half of the time when outside in the summer sun (Arch Ophthalmol. 2004 May;122(5):750-7). An increased exposure to 'blue light' has been reported to increase macular degeneration development.

Recently published data shows that persons with previously controlled hypertension (blood pressure less than 160/95) were approximately twice as likely, and persons with uncontrolled hypertension (blood pressure more than 160/95) were approximately thrice as likely, to develop wet macular degeneration than persons with normal blood pressure (Ophthalmology 2003;110: 636-643). In the Age-Related Eye Disease Study persons with hypertension were 1.5 times as likely to have wet macular degeneration compared with persons without hypertension.

If your blood pressure is 140/80, that means your systolic blood pressure is = 140 and your diastolic pressure = 80. The pulse pressure is calculated as follows: systolic blood pressure minus diastolic blood pressure. Therefore in this example your pulse pressure would be 60 (140 minus 80). In general, higher systolic pressure and higher pulse pressure are associated with higher risk of wet macular degeneration. (The pulse pressure would be high if the systolic pressure is high and the diastolic pressure is low). Higher pulse pressure and lower diastolic blood pressure may therefore be markers for degenerative changes occurring in eyes that are at risk for wet macular degeneration development.

Physical activity like brisk walking, jogging, bicycling, etc., long enough to work up a sweat when performed regularly (more than 3 times a week) reduces the rate of progression to advanced macular degeneration by 25%. According to CDC recommendations, adults should strive to meet either of the following physical activity schedules of either moderate or vigorous physical activity

. Adults should either engage in moderate-intensity physical activities for at least 30 minutes on 5 or more days of the week or adults should engage in vigorous-intensity physical activity 3 or more days per week for 20 or more minutes per occasion. You can incorporate a combination of flexibility, cardiorespiratory, and strength physical activity components

into your routine. Doing activities in all three areas is important in creating a balanced physical activity plan. (Sample activity schedule

for older adults).

A sedentary lifestyle may result in obesity, which has been found to be associated with macular degeneration. Body Mass Index (BMI)

correlates with body fat

. If the BMI is 30 or more, the likelihood of developing advanced macular degeneration increases by about 2.5 times. (Find your BMI using web-calculator

or BMI chart

)

Is chronic inflammation the underlying common mechanism that links macular degeneration and cardiovascular disease?

The discovery of macular degeneration gene (CPH gene variant is involved in regulating the inflammatory pathways) lends support to this hypothesis. Recent research provides additional support. High blood levels of two biomarkers of inflammation - C-reactive protein (CRP) and interleukin 6 (IL-6) - are associated with a twofold increase in the risk of progression of macular degeneration from early and intermediate stage to advanced stage over a 5 year period. Reducing inflammation and the levels of CRP and IL-6 may retard the progression of macular degeneration. One possible treatment to reduce CRP and IL-6 levels would be statin medications like Lipitor, Zocor and Norvir. There have been a few conflicting reports regarding the potential beneficial effect of statin therapy in reducing the risk of AMD. The benefit of long-term anti-inflammatory treatment in macular degeneration remains to be established. (Arch Ophthalmol. 2005 Jun;123(6):774-82)

High fat intake is associated with an increased risk of macular degeneration in both women and men. Our diet contains two types of fat (saturated and unsaturated). is made when manufacturers add hydrogen to vegetable oil--a process called hydrogenation. Hydrogenation increases the shelf life and flavor stability of foods containing these fats. Both types (saturated & unsaturated) are associated with an increase in risk of macular degeneration. Surprisingly, even increased intake of polyunsaturated fats (the good fat), which have a protective effect against heart diseases, do not have a similar protective against macular degeneration. Recent research has shown that although increasing the intake of all types of polyunsaturated fats does not help in macular degeneration, preferentially increasing intake of one type of polyunsaturated fat and simultaneously reducing intake of another type of polyunsaturated fat does help. Linolenic acid (omega-3 fatty acid), which is a type of polyunsaturated fat found primarily in fish and flaxseed oil, is associated with lessening of macular degeneration risk, but only among individuals with lower intake of linoleic acid (omega-6 fatty acid). Therefore, intake of food sources with high linolenic acid (omega-3 fatty acid) and low linoleic acid (omega-6 fatty acid), as is found in Canola oil may help in macular degeneration. (View the 'Trans Fat' video 56K

or cable/DSL

The Bad

Of the food sources, intake of beef, pork, or lamb as a main dish increases the risk of macular degeneration. More than 1 serving/week of beef, pork, or lamb as a main dish is associated with a 35% increased risk of macular degeneration as compared with less than 3 servings/month. A high intake of margarine is also significantly related to an increased risk of macular degeneration. 1 serving per day of high-fat dairy food (whole milk, ice cream, hard cheese, or butter) increases risk of macular degeneration progression by 1.91 times. 1 serving per day of meat food (hamburger, hot dogs, processed meat, bacon, beef as a sandwich, or beef as a main dish) increases risk of macular degeneration progression by 2.09 times. 1 serving per day of processed baked goods (commercial pie, cake, cookies, and potato chips) increases risk of macular degeneration progression by 2.42 times.

The Good

People who eat fish more than 4 times/week have a lower risk of macular degeneration than those who consume it less than 3 times/month. This is especially true for Tuna fish. People who eat canned tuna more than once per week are 40% less likely to develop macular degeneration as compared with those who consumed it less than once per month. Fish is a major source of DHA (an omega-3 fatty acid). Recently it has been reported that there is a potential beneficial effect of eating any type of nuts on risk of progression of macular degeneration. Eating 1 serving per day of any type of nut reduces the risk of progression of macular degeneration by 40%. This beneficial effect complements other literature reporting a protective role for nuts and cardiovascular disease and type 2 diabetes mellitus. One of the bioactive compounds in nuts, resveratrol, has antioxidant, antithrombotic, and anti-inflammatory properties.

AgingEye Times recommendation: Fat provides about 42 percent of the calories in the average American diet. A diet that derives closer to 20-25 percent of total calories from fat is probably healthier. Reducing fat intake to this level means cutting down greatly on consumption of red meats and dairy products such as milk, cheese, and butter. Eating more cold-water fish (at least twice weekly), rather than red meats and eating any type of nuts may help macular degeneration patients. Women must read the FDA advisory on the levels of mercury in fish

prior to increasing the consumption of fish.
(References: Arch Ophthalmol.2000;118:401-4, Arch Ophthalmol.2001;119:1191-9, Am J Clin Nutr 2001;73:209-18, Arch Ophthalmol 2003 Dec;121:1728-37)

Several large scale studies have assessed the association between cataract surgery and macular degeneration risk, but there seems to be no consensus on this issue. However, when data from the three major population based studies were pooled, the odds of having macular degeneration were found to be 1.7 times higher after cataract surgery than without cataract surgery (Am J Ophthalmol 2003;135:849-56).

There are several possible reasons for this increased risk of macular degeneration after cataract surgery. One possibility is that cataract and macular degeneration simply share one or more common risk factors or developmental pathways. With aging, a person develops both a dense cataract as well as macular degeneration, and therefore regardless of whether you have cataract surgery or not, the risk of having macular degeneration progressively increases. Another explanation is the 'blue-light hypothesis'. In this hypothesis, removal of the cataract newly exposes the retina to certain wavelengths of light (or at greater intensity), damaging the retina and increasing the risk of macular degeneration. As most of the intraocular lens implants currently in use have ultraviolet-B blockers, the critical wavelengths are likely to be in the blue light region. Further investigations of this hypothesis is needed.

AgingEye Times recommendation: Although there are several unanswered questions about 'blue light' damage to the macula, based on the growing body of evidence, we suggest using appropriate measures to limit blue light exposure to the macula. There are 2 strategies one can use. The first is to increase the intake of green leafy vegetables and/or lutein & zeaxanthin supplements. These macular pigments filter the blue light as it hit the retina and therefore help to prevent macular damage. The second strategy is to wear 'blue blocking' glasses. The color that blocks blue is yellow, so blue blockers must contain a yellow tint. There are ready-made "NOIR" sunglasses

that block blue and UV light with a variety of tints, including light yellow, dark yellow, amber, and plum. NOIR glasses are available as clip-ons, and as large plastic frames that fit over your regular glasses. You can also ask your local optical shop to make you a pair of UV and blue blocker glasses or add blue blockers to your existing glasses.

Recently FDA has approved an intraocular lens (IOL) that blocks blue-light (ACRYSOF Natural Lens

manufactured by Alcon, Inc). The hope is that after implantation of this IOL after cataract surgery, the effects of blue-light on the retina will be blocked. However, there are lingering concerns about vision under low lighting conditions and color vision quality despite evidence presented by the manufacturer to dispel such concerns.

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