Macular Degeneration: Types, Causes, and Possible Interventions

Macular Degeneration: Types, Causes, and Possible Interventions Alice Feret, EdD, Sue Steinweg, PhD, Harold C. Griffin, PhD, and Sherrill Glover, OD, PA Macular degeneration is the most common cause of blindness in individuals over 50 years of age. The condition is frequently classified into the categories of early, intermediate, and advanced stages. Current interventions concerning macular degeneration include a healthy lifestyle, diet, medical intervention, surgery, and environmental assistance. Future strategies for individuals with macular degeneration will possibly stress gene therapy, retinal transplantation, artificial vision, retinal prosthesis, and neuroprotection. (Geriatr Nurs 2007;28:387-392) acular degeneration is a disorder of the central retina, frequently related to the aging process. The macula is the part of the retina where the images are very clear. When the cells in the macula degenerate, only peripheral vision remains. The condition can be bilateral, but the onset is usually asymmetric. A person with macular can no longer see the details of an image. Macular degeneration appears to increase with advancing age.1 Schutt and Holz2 reported that age-related macular degeneration is the most common cause of blindness in individuals aged over 50 years and is the second most common cause of visual loss in adults following diabetes. Women seem to suffer from macular degeneration more than men; Caucasians and Asian Americans seem to be more vulnerable than African or Mexican Americans.3 Macular degeneration affects central vision and distance visual acuity, near visual acuity, color discrimination, contrast sensitivity, and other sense functions. It affects the ability to read, to recognize people’s faces, to choose clothes, to view pictures, and to play or view sports.1 The editors of The Harvard Health Letter4 examined some early warning signs of this condition. These warning signs included difficulty reading, difficulty driving, increased reliance on bright light, and an awareness of a blurry spot in the middle of vision.

M

Types and Characteristics Early Age-Related Macular Degeneration A possible classification of age-related macular degeneration are the categories of early, intermediate, and advanced stages of the condition. Murray3 stated that 70%-90% of the cases of age-related macular degeneration are caused by the early form of the condition. Seddon5 and Murray3 reported that the early stage of agerelated macular degeneration is characterized by several small or a few medium-sized drusen in 1 or both eyes, macular thinning, and pigment changes in the macula. Although the early form of age-related macular degeneration is frequently self-limiting and often stabilizes, vision loss with the early form is not significant but permanent. Some of the visual characteristics of the early form of age-related macular degeneration include words appearing in a blurry form and colors that are dim or gray. Fraser6 reported that individuals with early age-related macular degeneration may have increasing difficulties with small print and problems recognizing faces. Intermediate Age-Related Macular Degeneration The intermediate form of age-related macular degeneration is characterized by larger drusen development and at times more pigment changes in the macular. Also, the intermediate form of the condition is often accompanied by noncentral atrophic retinal changes in 1 or both eyes.5 The vision of an individual is mildly affected and therapy is available. Advanced Age-Related Macular Degeneration A third form of age-related macular degeneration is the advanced form of age-related macular degeneration. In this form of macular degeneration, the development of central geographic atrophy or neovasularization of the choroid occurs. The scar tissue that forms beneath

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Table 1. Foods Used in the Possible Prevention and Modification of the Developmental Speed of Age-Related Macular Degeneration Factor

Food

Beta-carotene Palm oil, oral supplements Leutin Green plants, carrots, spinach, fruits, oral supplements, kale, spinach, broccoli, peas, brussels sprouts Zeaxanthin Spinach, corn, fruits, oral supplements, kale, spinach, broccoli, peas, brussels sprouts Lycopene Tomatoes, carrots, apricots, and oral supplements Vitamin C Citrus fruits, sweet peppers Vitamin E Vegetable oils, nuts, green leafy vegetables, fortified cereals Zinc Red meat, poultry, beans, nuts, seafood, whole grains, fortified cereals, and dairy products

the retina causes permanent damage to the macula. In the exudative form of advanced macular degeneration, neovascularization occurs, and hemorrhages result in scar tissue and tissue degeneration. The visual loss in the advanced form is more rapid and severe than visual loss associated with the dry form.1 One in 10 patients with early, age-related macular degeneration will develop the advanced form.4

Interventions A number of initiatives may help slow the progression of macular degeneration. These include maintaining a healthy blood pressure, promoting healthy cholesterol levels, eliminating smoking, and wearing sunglasses that include ultraviolet ray reduction. Early Age-Related Macular Degeneration A key intervention in the early form of agerelated macular degeneration is observation. Regular checkups by an ophthalmologist or an optometrist are needed. Fraser6 suggests that individuals over forty years of age should have their sight tested every 2 years. Intermediate Age-Related Macular Degeneration In the intermediate form of age-related macular degeneration, dietary interventions are considered for individuals with the condition. Dietary interventions that stress the use of antioxidants and include the use of zinc, vitamin

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C, vitamin E, copper, and beta-carotene7 seem to be of help to individuals with age-related macular degeneration. The dietary interventions seem to be more beneficial for individuals with moderate age-related macular degeneration. The dietary interventions seem to slow the progression to the severe stages of the condition. Leutin and zeaxanthin are carotenoid plant pigments naturally found in the macula, which help to protect the retina and retinal pigment epithelium (RPE) from light initiated damage. Johnson8 reported the leutin and zeaxanthin function as antioxidants and provide blue light filters. Foods known to have the highest amount of lutein and zeaxanthin are kale, spinach, broccoli, peas, and brussels sprouts (Tables 1 and 2). Advanced Age-Related Macular Degeneration A number of interventions are being utilized for advanced age-related (wet) macular degeneration. These interventions are anti–vascular endothelial growth factor (VEGF) therapy, photodynamic therapy (PDT; with or without intraocular steroids), thermal laser, and submacular and translocation surgery. Also the geographic atrophy form of advanced age-related macular degeneration uses low vision aids and observation as part of possible therapeutic intervention approaches.

Medical Interventions Several new treatments are in use while others are undergoing testing. These interventions

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Table 2. Nutritional Elements That May Reduce the Occurrence and Severity of Macular Degeneration Element

Possible Daily Amount

Foods

Beta-carotene Leutin

15 mg 10 mg

Palm oil, oral supplements Green plants, carrots, spinach, fruits, oral supplements, kale, spinach, broccoli, peas, brussels sprouts Spinach, corn, fruits, oral supplements, kale, spinach, broccoli, peas, brussels sprouts Fish (salmon, tuna, mackerel, herring), soybean, canola, flaxseed oils, walnuts, and leafy greens Tomatoes, carrots, apricots, and oral supplements Citrus fruits, sweet peppers Vegetable oils, nuts, green leafy vegetables, fortified cereals Red meat, poultry, beans, nuts, seafood, whole grains, fortified cereals, dairy products Shellfish and nuts

Zeaxanthin

2 mg

Omega-3 fatty acids Lycopene Vitamin C Vitamin E

3 g (2 g of the 3 g may be from supplements) 23 mg 500 mg 400 IU

Zinc

80 mg (zinc oxide)

Copper

2 mg 20

Data from Yeung

and Stokkermans.21

can help in the treatment of age-related macular degeneration. Therapies Used Anti-VEGF Therapy. VEGF has become a major target in the treatment of macular degeneration. Anti-VEGF therapy is the most common form of treatment of the advanced form of macular degeneration. At times VEGF is inflammatory, causes abnormal or pathologic angiogenesis, and increases vascular permeability.9 Gerson9 pointed out that VEGF is needed for normal angiogenesis. Normal angiogenesis helps to promote normal cell development and healing. Anti-VEGF therapies must eliminate pathologic vessels and spare normal vessels. Several anti-VEGF drugs have been approved. These include Macugen and Lucentis. Avastin is not approved but is widely used. Other anti-VEGF drugs currently are being evaluated in clinical trials.9 Photodynamic Therapy. Combining the use of low-energy light and a photosensitizing agent to cause vascular occlusion has reduced the risk of moderate visual loss for some patients at 12 and 24 months after treatment. This therapy assists in the stabilization of vision and the prevention of further visual loss. Negative factors are the high cost of drugs, the need for more treatments, and possible continuing visual decline

even with treatment.10 Gerson9 reported that photodynamic therapy can cause severe visual loss, inflammation, and greater release of the VEGF protein, causing choroidal neovascularization (CNV). Thermal Laser Treatment. Ablation of CNV with laser is another treatment. The advanced form of age-related macular degeneration can be helped by a laser surgery called thermal laser photocoagulation. Sealing the leaking blood vessels in the advanced type of macular degeneration can slow down the damage to the eye.11 The disadvantages of thermal laser treatment may include permanent and immediate loss of vision. Macular Translocation. In this therapy, the retina is detached and shifted from the neovascular complex to normal retinal pigment epithelial cells. This approach permits the CNV to be treated with various therapies. Results of macular translocation are good in selected cases, but the risks include retinal detachment, macular pucker, increased lens opacity, and tilted image.10 Therapies in Clinical Trial Feeder-Vessel Laser. This therapy is characterized by laser-induced occlusion of the feeder arteries to the retina to prevent growth of capillaries and prevent leakage in the macula area.

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Table 3. Visual Aid Resources for Individuals with Macular Degeneration Instrument

Web Site

Costs

Aladdin Companion (video magnifier) www.telesensory.com $1,595-$3,300 Telescopic devices www.designsforvision.com/LVhtml/LVtel.htm Varies (starting at $50) Hand magnifiers www.macula.org/low_vision/devices.html $20-$50 Fluorescent lamps www.forlights.com $120-$200 Merlin (auto-focus desktop magnifier) www.enhanced vision.com $2,000-$3,075 Glare-protective devices www.sightconnection.com/eyewear.html $2-$5 Jordy (head-held magnification) www.enhancedvision.com $2,700-$4,000 Primer Electronic Magnifying Reader www.independentliving.com $300

Antiinflammatory Therapy. This is treatment of CNV (neovascular complex) with PDT and antiinflammatory agents (triamcinolone acetone). The therapy seems to improve visual acuity and requires less frequent treatments. Broad-Acting Antiangiogenic Drugs. This therapy uses endothelial activation, invasion, proliferation, and differentiation. Targeted Molecular Therapy. Antiangiogenic therapy uses targeted molecular therapy, such as anti-vascular endothelial growth factor. Gene Therapy. This approach moves a gene into a target cell so that the cell can synthesize the protein of the gene. Surgical Trials. Surgical removal of CNV may not destroy all central macular photoreceptors. The initial trials indicate that surgical removal of the CNV does not seem to improve visual acuity of individuals aged over 50 years.

Environmental Interventions Many interventions exist to assist individuals who are visually impaired. Rohrschneider and Blankenagel12 described various methods of magnification. These include reducing the distance, enlargement of the text, and magnifying objects. Text print can be enlarged through copying machines or printed by publishers. Based on the ideas of design incorporated with the use of low vision aids, universal design focuses on the use of space and technology to create opportunities for all, including individuals with disabilities. Categories of low vision aids that magnify (Table 3) include handheld, stand, illuminated, video, and head-born magnifiers, as well as various types of telescopes for

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distance vision.13 Burggraaff and colleagues14 reported that the most frequently used lowvision aids include closed circuit television, telescopic devices, hand magnifiers with and without illumination, stand magnifiers with illumination, fluorescent lamps, and glare-protective devices. Some low-vision aids shift images to the periphery of the eye to produce clearer images. Aids to help individuals with reduced vision are constantly being created. The Merlin is a desktop video magnifier that uses color and black and white in the visual field with a voice activation feature. The Aladdin Companion is a closed-circuit television, providing magnification up to 17.5⫻. It can be used in reverse contrast with a white on black background to help people read. The Jordy is a head-held device that can be used in color or black and white; it helps people see at a distance or up close. The Primer is an electronic reader, primarily used for reading by people with retinal disease. It magnifies from 30-60 diopters without the complications of higher-power optical magnification.15

Future Trends Improved treatments of macular degeneration under study include gene therapy, human retinal transplantation, artificial vision, retinal prosthesis, and neuroprotection. The insertion of modified genes into a target organ to change the cell function is using vector encoding as an antiangiogenic factor. Lavaque and colleagues16 reported that clinical trials in gene therapy are currently being conducted.

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Human retinal transplantation includes the transplantation of retinal cells both to halt the disease process and to improve visual functioning. It can reverse damage to photoreceptors and choriocapillaries with early surgical intervention. Improved surgical techniques involving less inflammation and fewer problems with the blood-retinal barrier seem to offer a better chance of successful retinal transplantation than in the past, especially with the dry form of age-related macular degeneration.17 Artificial vision also has been tested with success at several intervention points: the retina, optic nerve, and occipital cortex. Awdeh and colleauges18 stated that visual stimulation of the fovea has resulted in individuals being able to read 36-point font size. Artificial vision uses either an internal or an external approach. The internal approach does not require external power or cameras18 but uses a subretinal microelectrode array between the bipolar cell layer and the retinal pigment epithelium. The external approach (epiretinal) uses a camera built into glasses and a small visual processing unit with a small microelectric chip, sending an image from the external camera to the implanted portion of the prosthesis. The neuroprotection approach attempts to maintain functioning of neurons as well as prevent neurons from dying. It blocks the development of elevated concentrations of glutamate and reduces the production of toxic nitric oxide. Tombran-Tink and Branstable19 noted that developing pigment epithelium– derived factor peptides will help diseases, such as macular degeneration, that are marked by neovascular conditions.

Summary Currently, prevention and intervention are associated with diet, surgery, and a healthy lifestyle. Because the medical community does not have a definitive treatment for macular degeneration, a better quality of life for individuals with macular degeneration is linked to the identification and use of individual specific low-vision aids, as well as the organization of technology and living spaces through the use of universal design. Macular degeneration continues to present a challenge to individuals who are striving for independence in functioning, as well as to professionals looking for intervention

strategies that might prevent or alter the nature of the condition.

References 1. Lovie-Kitchen J, Bowan K. Senile macular degeneration. Boston, MA: Butterworth; 1985. p. 130-5. 2. Schutt F, Holz F. Age-related macular degeneration: current concepts of pathogenesis and risk factors. In: Alberti W, Richard G, Sagerman R, editors. Age-related macular degeneration. Current treatment and concepts. New York: Springer Publishing Company; 2001. p. 1-3. 3. Murray L. Macular degeneration. In: Long J, editor. Gale encyclopedia of medicine. 2nd ed. Farmington Hill, MI: Gale Group; 2001. p. 592-7. 4. Lee T. The latest on macular degeneration. Harvard Health Letter 2003;28:7-12. 5. Seddon J. Macular degeneration. Rev Optometry 2006; 77:62-6. 6. Fraser S. Ageing of the eye: practical tips. Clin Pulse 2004;64:50-1. 7. Gordon J, Schooff M. Can high-dose supplementation with vitamins C and E, beta carotene, and zinc slow the progression of macular degeneration? J Fam Pract 2002;51:105-7. 8. Johnson E. Obesity, lutein metabolism, and age-related macular degeneration: a web of connections. Nutr Rev 2005;65:9-15. 9. Gerson J. Vascular endothelial growth factor: a new frontier in macular degeneration. Rev Optometry 2006; 113:4-5, 14. 10. Cousins S, Csaky, K, Espinosa-Heidmann, G. Clinical strategies for diagnosis and treatment of AMD: implications from research. In: Penfold P, Provis J, editors. Macular degeneration. Heidelberg, Germany: Springer Publishing Company; 2005. p. 167-89. 11. What is laser surgery for age-related macular degeneration? Clin Ref Syst 2002;8:1922. 12. Rohrschneider K, Blankenagel A. Magnifying reading aids in AMD. In: Holz F, Pualeikhoff D, Spaide R, et al., editors. Age-related macular degeneration. New York: Springer Publishing Company; 2004. p. 213-30. 13. Meszaros, L. The lowdown on low vision aids. Ophthalmol Times 2004;29:35-7. 14. Burggraaff M, van Nispen R, de Boer M, et al. Optometric and multidisciplinary approaches in prescribing low vision aids. Vis Impairment Res 2005; 7:71-8. 15. All eyes on low vision products: From magnifiers to lighting solutions. Ophthalmol Times 2004;29:35-7. 16. Lavaque A, Liggett P, Brucker A, et al. Introduction to gene therapy and related techniques for retinal disorders and age-related macular degeneration. In: Alfaro D, Liggett P, Mieler W, et al., editors. Age-related macular degeneration: a comprehensive textbook. Philadelphia: Lippincott, Williams, and Wilkins; 2006. p. 300-13. 17. Binder S. Human retinal transplantation. In: Alfaro D, Liggett P, Mieler H, et al., editors. Age-related macular degeneration: a comprehensive textbook. Philadelphia: Lippincott, Williams, and Wilkins; 2006. p. 314-27. 18. Awdeh R, Lakhanpal R, Weiland J, et al. Artificial vision, visual prosthesis, and retinal implants. In:

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Alfaro D, Liggett P, Mieler H, et al., editors. Age-related macular degeneration: a comprehensive textbook. Philadelphia: Lippincott, Williams, and Wilkins Publishers; 2006. p. 328-34. 19. Tombran-Tink J, Barnstable C. Neuroprotection in macular degeneration. In: Alfaro D, Liggett P, Mieler H, et al., editors. Age-related macular degeneration: a comprehensive textbook. Philadelphia: Lippincott, Williams, and Wilkins Publishers; 2006. p. 335-47. 20. Yeung D. Dietary lycopene and its possible association with reduced levels of oxidative damage and chronic diseases. Available at: www.lycopene.org/documents/ html. Cited January 30, 2007. 21. Stokkermans T. Can patients eat their way to improved vision? Rev Optometry 2005;112:9-10.

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ALICE FERET, PhD, is an assistant professor in the Department of Curriculum and Instruction, East Carolina University, Greenville, North Carolina. SUE STEINWEG, PhD, is an assistant professor in the Department of Curriculum and Instruction, East Carolina University, Greenville, North Carolina. HAROLD C. GRIFFIN, PhD, is an associate professor in the Department of Curriculum and Instruction, East Carolina University, Greenville, North Carolina. SHERRILL GLOVER, OD, PA, is an optometrist in private practice at Princeton Family Eye Care, Princeton, North Carolina. 0197-4572/07/$ - see front matter © 2007 Mosby, Inc. All rights reserved. doi:10.1016/j.gerinurse.2007.03.003

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