Macular Degeneration - Retinal Disorders

MACULAR DEGENERATION

Macular degeneration is the most common cause of visual loss in people older than age 60 (Margolis et al., 2002). Commonly called age-related macular degeneration (AMD), it is character-ized by tiny, yellowish spots called drusen (Fig. 58-13) beneath the retina. Most people older than 60 years of age have at least a few small drusen. There is a wide range of visual loss in patients with macular degeneration, but most patients do not experience total blindness. Central vision is generally the most affected, with most patients retaining peripheral vision (Fig. 58-14). There are two types of AMD, commonly known as the dry type and wet type.

Between 85% and 90% of people with AMD have the dry or nonexudative type in which the outer layers of the retina slowly break down (Fig. 58-15). With this breakdown comes the ap-pearance of drusen. When the drusen occur outside of the mac-ular area, patients generally have no symptoms. When the drusen occur within the macula, there is a gradual blurring of vision that patients may notice when they try to read. There is no known treatment that can slow or cure this type of AMD.

The second type of AMD, the wet or exudative type, may have an abrupt onset. Patients complain that straight lines appear crooked and distorted or that letters in words appear broken up. This effect results from proliferation of abnormal blood vessels growing under the retina, within the choroid layer of the eye, a condition known as choroidal neovascularization (CNV). The affected vessels can leak fluid and blood, elevating the retina. Some patients can be treated with the laser to stop the leakage from these vessels. This treatment is not ideal because vision may be affected by the laser treatment and abnormal vessels often grow back after treatment.

Medical Management

PHOTODYNAMIC THERAPY

Visual loss from CNV lesions in AMD is a growing problem. With the growth of these new vessels from the choriocapillar layer, fibrous tissue develops that can, over months, destroy cen-tral vision. Laser treatment has been used to close these abnor-mal vessels, but the very process of photocoagulation carries with it some level of retinal destruction, albeit less than the natural scarring that would occur in the untreated eye. Photodynamic therapy (PDT) has been developed in an attempt to ameliorate the CNV while causing minimal damage to the retina. The Treatment of Age-Related Macular Degeneration With Photo-dynamic Therapy (TAP) study group (1999) has shown that PDT can reduce the risk of visual loss for certain groups of pa-tients who have classic subfoveal choroidal neovascularization due to macular degeneration.

PDT is a two-step process (Fig. 58-16). Verteporfin, a photo-sensitive dye, is infused intravenously over 10 minutes. Fifteen minutes after the start of the infusion, a diode laser is used to treat the abnormal network of vessels. The dye within the vessels takes up the energy of the diode laser, but the surrounding retina does not, avoiding damage to adjacent areas. Retreatment may be nec-essary over time.

Nursing Management

Nursing management is primarily educational. Verteporfin is a light-activated dye, and patient education is important preoperatively. The patient should be instructed to bring dark sunglasses, gloves, a wide-brimmed hat, long-sleeved shirt, and slacks to the PDT setting. The patient must be cautioned to avoid exposure to direct sunlight or bright light for 5 days after treatment. The dye within the blood vessels near the surface of the skin could become activated with exposure to strong light. This would include bright sunlight, tanning booths, halogen lights, and the bright lights used in dental offices and operating rooms. Ordinary indoor light is not a problem. If a patient must go outdoors within the first 5 days after treatment, he or she should be counseled to wear long-sleeved shirts and slacks made of tightly woven fabrics. 

Gloves, shoes, socks, sunglasses, and a wide-brimmed hat should also be worn if the patient has to go outdoors during daylight hours during this period. Inadvertent sunlight exposure can lead to severe blistering of the skin and sunburn that may require plas-tic surgery.

Macular Translocation

Wet macular degeneration is characterized by the development of an abnormal CNV membrane to the detriment of central vi-sion. One approach to this problem is the surgical procedure known as macular translocation, in which a 360-degree retinal detachment is surgically created and the retina is gently lifted and resettled, placing the macular area a slight distance away from thearea of CNV. Laser treatment can then be applied to the abnor-mal neovascular network with minimal damage occurring to the macula. Pilot studies are evaluating whether this surgical ap-proach is an effective alternative to laser treatments of CNV due to AMD.

Angiogenesis

An important component of the effort against neovascular AMD is the investigation into the causes of the development and pro-gression of angiogenesis (ie, abnormal blood vessel formation). Investigations continue in the laboratory to search for agents that can inhibit angiogenesis. This has implications for ocular neovascularization and treatment of other disorders such as solid tumors.

Management

Most patients benefit from the use of bright lighting and magni-fication devices and from referral to a low-vision center. Some low-vision centers send representatives into the patient’s home or place of employment to evaluate the living and working condi-tions and make recommendations to improve lighting, thereby improving vision and promoting safety. The home care nurse can make the same assessment and recommendations.

Amsler grids are given to patients to use in their home to mon-itor for a sudden onset or distortion of vision. These may provide the earliest sign that macular degeneration is getting worse. Patients should be encouraged to use these grids and to look at them, one eye at a time, several times each week with glasses on. If there is a change in the grid (eg, if the lines or squares ap-pear distorted or faded), the patient should be instructed to no-tify the ophthalmologist immediately and to arrange to be seen promptly.

The Age-Related Eye Disease Study Group (2001), a multi-center clinical trial, has provided promising information about the prevention and treatment of AMD. The study was designed to determine whether large doses of macronutrients are effective in preventing or slowing the course of AMD. The study revealedthat use of antioxidants (ie, vitamin C, vitamin E, and beta-carotene) and minerals (ie, zinc oxide) can slow the progression of AMD and vision loss for people at high risk for developing advanced AMD.