Monday, February 22, 2016

age-related macular degeneration

Fundus cupcake sprinkled with drusen
February is Age-related Macular Degeneration (AMD) Awareness Month. AMD is one of the leading causes of irreversible vision loss among Americans over 60 (1)

Let's preface our AMD discussion with a quick anatomy review. The tissue that lines the back of the eye is called the retina. The retina has millions of light-sensing cells called photoreceptors (rods and cones). These cells absorb light and convert it into signals that are sent to the brain via the optic nerve, allowing us to see the world around us. The macula is a small area near the center of the retina that is responsible for our central, sharpest vision. Within the macula is a high density of cones, the photoreceptors responsible for color vision. When you look at retinal photos (or the cupcake above), the macula is the dark red area. For reference, here is a labeled photo of a healthy retina.

What is age-related macular degeneration?
Age-related macular degeneration, commonly called AMD or ARMD, involves a breakdown of the tissue that makes up the macula. Waste products called drusen accumulate beneath the retina, in and around the macula. Drusen are the yellow-ish deposits you see in the photo below. This disruption causes the photoreceptor cells to die, which impairs vision. Over time, central vision becomes blurry and distorted. AMD can be classified as either dry or wet.  
  • Dry (non-exudative) AMD: This is the most common form of the disease. The early and intermediate stages of dry AMD involve drusen and/or pigmentary changes in the retinal pigment epithelium (RPE). The late stage involves the death of large areas of retinal tissue, called geographic atrophy, which affects central vision significantly.
Fundus photo of dry AMD
  • Wet (exudative) AMD: About 10% of dry AMD cases progress to the wet form, meaning that neovascularization has occurred. Neovascularization is the formation of new, abnormal blood vessels under and into the retina. These vessels are weak and can leak, causing vision loss. Neovascularization is bad news bears and warrants prompt treatment (discussed below). Wet AMD typically affects vision more rapidly and more significantly than dry AMD.

What are the risk factors?
AMD is a multifactorial disease. The exact cause is unknown, but research suggests some factors increase the risk of AMD:

  • Age. Age is a major risk factor, with most cases typically occurring after the age of 50. 
  • Smoking. Several studies have found a positive association between smoking and the development of AMD. The risk of developing the disease for current smokers is at least two to three times greater than the risk for non-smokers (2, 3). Smoking is the leading modifiable risk factor for AMD.
  • Family history/genetics. Having a close relative with AMD increases the risk of developing the disease (4). Researchers have identified variants of a few complement genes that are associated with an increased risk of developing AMD (5).
  • Diet. Those with diets low in omega-3 fatty acids and antioxidants may be at greater risk of progression to advanced disease (6).
  • Hypertension. Some studies have shown wet AMD to be associated with moderate to severe hypertension (78).
  • Obesity. Research has suggested an association between body mass index (BMI) outside the normal range and early AMD (9)  as well as progression to advanced AMD (10).
  • High cholesterol. Elevated high-density lipoprotein (HDL) levels may be associated with higher risk of AMD (11).
  • Sun exposure.  Exposure to large amounts of visible and blue light may play a factor in disease progression (121314)
  • Ethnicity. AMD is more prevalent in Caucasians. 
  • Gender. AMD is more prevalent in females.

How is AMD diagnosed?
AMD is diagnosed during a dilated eye exam. It may manifest itself in changes in central vision, but it most likely will not in the early stages. Upon dilation, pigmentary changes and/or drusen may be noted by your eye doctor in/around the macula. 

How it is monitored and treated?
  • Various tools exist to help monitor AMD and guide treatment: 
    • Retinal photo. Periodic photos allow for monitoring progression over time. 
    • Amsler grid. This is an easy way for patients to monitor for changes in their central vision. AMD can cause parts of the grid to appear distorted or missing. I suggest that my AMD patients leave it on their refrigerator and test each eye a few times a week, monitoring for any changes. 
      • The ForeseeHome monitoring device utilizes a similar concept. Patients are presented with a series of straight lines containing a wave/bump, and the patient must identify where the distortion is. The device collects the data and alerts the patient's eye doctor if there are abnormal results. 
    • Optical Coherence Tomography (OCT).  A scanning laser is used to image the tissue of the back of the eye. It can produce a cross section of the macula, showing retinal thinning or thickening.  
OCT showing drusen (red arrows) below the retina

    • Fluorescein angiography (FA). Fluorescein dye is injected into a vein in the arm and photos of the retina are taken as the dye reaches the retinal vessels. An FA may be ordered to identify neovascular membranes, evaluate leakage, and/or guide treatment. 
    • Coming down the pike: OCT Angiography. This technology just got FDA approval in the US. It will allow doctors to image the vessels of the retina and choroid without injecting a contrast dye (unlike an FA). 
  • Treatment: 
    • Dry- There is no FDA-approved treatment for dry AMD as of yet. Plenty of research is being done in this area. Studies have shown that antioxidant supplementation may help slow progression to advanced AMD (1516). For more information on ocular nutrition, check out this post.  
    • Wet- Most cases of wet AMD are treated with anti-vascular endothelial growth factor (VEGF) drugs. Anti-VEGF drugs are periodically injected into the eye to stop abnormal vessel growth. Photodynamic therapy (PDT) and laser photocoagulation are also treatment options, though less commonly used.
Vision loss is often life-altering and difficult to cope with. There are support groups and low-vision rehabilitation resources available to those dealing with AMD. Low vision aids include hand-held, stand, or spectacle magnifiers, video magnifiers (CCTVs), and even implantable telescopes! We'll do a separate post on low vision devices and rehab services later on, but here's a great place to begin: Living Well with Low Vision.

CliffsNotes: AMD is a multifactorial disease with several modifiable and non-modifiable risk factors. The best way to prevent vision loss from AMD is to have routine dilated eye exams, especially if you fall into a higher-risk category.   

Additional resources:

Sunday, February 14, 2016

Happy Valentine's Day!

Happy Valentine's Day!