courtesy of Dr. T.Mark Johnson MD FRCSC
Retina Group of Washington
Age related macular degeneration (AMD) is one of the leading causes of visual disability in people over the age of 60 in the developed world. The frequency of the disease increases with age so with the changing demographics of the population, AMD is becoming increasingly prevalent. In 2010, it was estimated that two million people in the United States suffered from AMD. Projections suggest that number will rise above three million by 2030 and reach five million by 2050.
While the primary risk factor for AMD is age, there are other important risk factors. AMD has a strong genetic component; patients that carry certain genes are at much greater risk for late stage macular degeneration, although these genes can be identified with non-invasive in-office tests. The most important modifiable risk factor for AMD is smoking.
AMD presents in two primary forms: dry (non-exudative) and wet (exudative). Dry macular degeneration is the earliest form of the condition and is characterized by an accumulation of drusen under the retina. Drusen is essentially waste material from the retina that accumulates over time. Wet macular degeneration develops when blood vessels grow abnormally under the retina leading to hemorrhaging and swelling.
Patients with macular degeneration lose vision because of two processes. A small percentage of those with dry macular degeneration develop a progressive loss of pigmentation in the macula leading to a gradual decline in vision referred to as geographic atrophy. Approximately 20% of patients develop wet macular degeneration that results from abnormal blood vessel growth under the retina and typically leads to a more rapid decline in vision. Patients with wet AMD often notice distortion of their vision.
Treatment for macular degeneration has improved greatly in the last decade. The Age-Related Eye Disease Study (AREDS) showed that high dose anti-oxidant vitamin therapy reduced the chances of developing advanced AMD in patients presenting the early stages of the disease. Drugs that block the growth of abnormal blood vessels can preserve and sometimes improve the vision of patients with wet AMD–and are most effective when wet AMD is detected early in its development. New technologies for home monitoring may help with early detection in high-risk patients—and new trials for dry macular degeneration are ongoing and showing some encouraging results.
Despite advances in therapy, there are still many patients that suffer visual disability from AMD. Progressive macular degeneration may lead to loss of central vision affecting activities such as reading, face recognition and driving. Macular degeneration spares the peripheral retina so that peripheral vision remains normal and patients never become completely blind.
Loss of central vision creates a need for greater magnification for close-up tasks. Magnification can be achieved with a variety of methods, including spectacles, hand-held or stand mounted magnifiers or video-assisted devices such as CCTV. Newer technologies such as the implantable telescope are expanding the scope and success of enhancing magnification.
A decrease in contrast vision often produces great difficulty. As contrast acuity declines, the background and foreground blur together with the central vision gradually becoming hazier. Contrast symptoms can vary significantly depending on lighting and viewing circumstances. Good and directed lighting is essential for optimal use of magnification devices. Reduction of glare using filtered lenses can enhance contrast indoors and outdoors. Use of digital readers allows patients access to high contrast reading screens and variable magnification in a portable device.
The management of AMD is complex and often is best handled by a team approach including an ophthalmologist that specializes in diagnosing and treating retinal disorders along with low vision optometrists and low vision therapists. With coordinated efforts the care of AMD patients continues to improve.