Macular Degeneration
by Ashley Dockx
Stephen F. Austin State University, Spring 2000
Return to Perception: Spring 2000 frontpage.
Robert, a 65 year-old male, has trouble reading fine detail, especially out of his central vision. He complains that his vision is blurred and that it is harder to see while operating a motor vehicle. In addition, sometimes objects appear wavy or crooked, which impairs his vision. His worst symptoms were that he occasionally lost the ability to distinguish between the features of familiar faces and he had a localized blind spot. Robert is not alone; many people suffer from symptoms related to loss and distortion of the visual field. He suffers from macular degeneration, the leading cause of decreased vision loss in the United States, especially for people over the age of 50 (Philippi, 2000).
Macular degeneration also known as late, aged-related maculopathy is an eye disorder which causes a decrease in the visual field known as the retinal macula (Medical Encyclopedia, 2000). The majority of people who are affected are people over the age of 65, but occasionally it develops earlier in people 40-50 years old (Philippi, 2000). The majority of the visual loss is located in the central part of the visual field, while the peripheral vision is unharmed. There are also two types of macular degeneration, the "wet" and "dry" forms. The "dry" form of this disease is the most popular, affecting 90% of the cases (American Academy of Ophthalmology, 1997).
Macular degeneration in general can affect many people in minor or drastic ways. People who experience this form often complain of vision loss when they are in dim light, especially when they are reading. The "dry" type is often characterized by a more gradual loss of vision compared to the "wet" type. Signs of this disease include an increase in drusen, which is an accumulation of a yellow-white substance, in the underside of the macular retina. A loss of cells can be seen in the macula. The macula is our sensitive sight region, where intricate detail can be seen. Thus, vision in this area is helpful and necessary to drive, read, focus on small details, and recognize familiar faces. The macula is located in the back of the eye known as the retina. The macula is only about 5 mm in diameter, and includes the fovea, which gives us our detailed central vision. If a person suffers from the "dry" form in one eye they will be more likely to develop it in the other eye as well.
In addition to, the "dry" form of macular degeneration, we must consider the "wet" form. Affecting 10% of the persons with macular degeneration this form can be very detrimental and severe (American Academy of Ophthalmology, 1997). The wet form is also referred to as the neovascular or exudative type (Cincinnati Eye Institute, 2000). This particular form takes a more progressive path and can affect the person more rapidly than the "dry" form. Also in a layer behind the retina, new blood vessels form in the choroids. The new blood vessels that develope tend to be on the outer side of the macula extending to the fovea. This process is known as choroidal neovascularization or a chorodial neovascular membrane (Cincinnati Eye Institute, 2000). Once the new vessels have developed they then begin to leak, which causes the separation of the layers, which then causes a retinal detachment. The gentleman mentioned at the beginning of this report, Robert, most likely experienced this form of macular degeneration, especially since he suffered from blurred vision and a localized blind spot in this visual field.
Both forms of macular degeneration have been linked to other family members, which makes this disease familial. Since scientists still today do not know the extent of this, we need to keep researching so perhaps we can stop this cycle before it affects more and more people.
Treatments are being developed everyday in this field of visual loss. The dry type of macular degeneration can be treated by the use of laser treatments (Medical Encyclopedia, 2000). Currently there is no known treatment to completely stop the formation or intensity of the dry form of macular degeneration. There is, however, research being done to see if vitamins and minerals will benefit the person affected with this disease. Also, researchers have begun to investigate if consuming dietary spinach or other green leafy vegetables can slow down the dry form of AMD (Cincinnati Eye Institute, 2000). On the other hand, new treatments of the wet form of macular degeneration are available and give people who suffer with this disease a sense of hope. According to the National Eye Institute, the treatment most commonly used to correct to reduce wet AMD is called laser photocoagulation (Philippi, 2000). In this laser procedure a small, vigorous light ray is directed into the eye, focusing on a tiny location on the macula. This focusing of light preserves the vision by destroying any unwanted blood vessels that have formed (Philippi, 2000). In this particular study vision loss was prevented and in some cases diminished extensively in over 50% of the cases. It is not the best solution for everyone who has this problem but has been known to help some. Using laser surgery is best if the problem is detected early on, so that the fovea is not damaged severely. This form of laser surgery is not used and will not help to diminish or extinguish the "dry" type of macular degeneration. Society will have to wait for later developments and research This laser surgery can not restore any previously lost vision, so if it was damaged badly there is no chance of visual recovery (Philippi, 2000). Also if a person with this disease goes through with the laser surgery, then continued treatments will be necessary so that additional growths on the retina can be detected (Cincinnati Eye Institute, 2000). The best way to decrease a person's chance of having progressed macular degeneration is to see an eye specialist if any symptoms occur or persist.
In the case of having the dry form of macular degeneration the person can not see with the naked eye the build up of drusen, so they should have a visual specialist examine their eye. Drugs can even be given to perhaps reduce this disease, for example thalidomide and antioxidant vitamins (Dr. Koop, 1999). If these techniques do not work perhaps radiation therapy or blood filtration procedures would be beneficial. Radiotherapy has also been influential in treating patients with choroidal neovascularization also known as CVN (Mauget-Faysse, et. al., 1999). Individuals also can check out their own eyes by using the Amsler Grid. This grid will give people a patterned grid, which a normal person can distinguish between but someone with AMD will see distortions. The person should use this technique on a daily basis so that they can realize changes sooner.
Current research supports the idea that macular degeneration may be a result of "overeager repair of mild injuries to retinal cells." An unhealthy, fatty diet may also increase the immune overreaction due to high concentrations of fat in the bloodstream.
On the other hand some research has been done to see if the result of the disease is influenced by "the gradual starving of retinal cells." (Seppa, 1999) Blood formation was a potential trigger for the formation of macular degeneration as well. At the University of Pennsylvania in Philadelphia researchers reported that patients with the "dry" form of AMD had a lower-than normal blood flow to the retina. This is perhaps due to the fact that poor circulation prevents nutrients from getting to the targeted area. This can also explain the idea that healthy people are less likely to develop the "wet" form of AMD if they already have experienced the "dry" form of this disease (Seppa, 1999). An additional study was done to test whether or not neovascular age-related macular degeneration is related to oxidative stress (Frank, Amin, & Puklin, 1999). They found that oxidative stress did in fact cause a pathologic upregulation of the enzymes heme oxygenase and lysosomal antigen. They also found diminishing catalase activity in both the macular and peripheral areas of the eye, especially with age (Frank, et al., 1999). Not only has research been done on macular degeneration in the United States but it has also been studied in European countries and even Japan (Kadonosono, Yazama, Itoh, Sawada, & Ohno, 1999). Their research provides us with the idea that choroidal neovascular membranes are responsible for the severe vision loss known as macular degeneration. This is becoming a growing problem with people who are becoming legally blind in areas like Japan (Kadonosono, et. al, 1999). Additional research also supports the finding that perhaps hypertension is a factor that impacts the outcome of poor vision (Owens, Guymer, Gross-Jendroska, & Bird, 1999). Perhaps if we knew more about what causes hypertension we could reduce our chances of getting a form of macular degeneration.
If someone suffers from macular degeneration they should be informed of the risks, prevention and devices used to adapt to a new lifestyle. There is really no known prevention, but if macular degeneration runs in a family consider a smoke-free lifestyle if you smoke currently (Yahoo Health, 2000). There are also many devices that help people with visual impairments manage everyday living more easily. People can use low-vision aids, which can enhance the images so that people can view slightly larger objects. Even though there is an extensive amount of information about macular degeneration, there is still more to be understood. Especially, because the magnitude of the problem is considerable.
References
Frank, R.N., Amin, R.H., & Punklin, J.E.(1999). Antioxident enzymes in the macular retinal pigment epithelium of eyes with neovascular age-realted macular degeneration. American Journal of Ophthalmology, 127 694-704.
Kadonosono, K., Yazama, F., Itoh N., Sawada, H., Ohno, S. (1999). Expression of Matrix Metalloproteinase-7 in Chroroidal Neovascular Membranes in Age-related Macular Degeneration. American Journal of Ophthalmology, 128,382-384.
Mauget-Faysse, M., Chiquet, C., Milea, D., Romestaing, P., Gerard, J.P., Martin, P., Koenig, F. (1999). Long term results of radiotherapy for subfoveal chorodial neovascularisation in age-related macular degeneration. American Journal of Ophthalmology, 128,781-782.
Owens, S.L, Guymer, R.H., Gross-Jendroska, M., & Bird A.C. (1999). Fluorescein Angiographic Abnormalities after Prophylactic Macular Photocoagulation for High-Risk Age-related Maculopathy. American Journal Of Ophthalmology, 127,681-687.
Philippi, K.,(2000). Macular Degeneration. The Health Connection.
Seppa, N. (1999). Physicians find clues to vision deterioration. Science News, 156, 215.
Websites:
Http://go.drkoop.com/conditions/macular_degeneration/page_49_238.asp
Http://www.cincinnatieye.com/laservisioncorection/eyedisordersand.htm
Http://209.64.11.10/Disease%20Cener/diseases/amd.asp