Macular Degeneration: Explained

What is macular degeneration?

Age-related macular degeneration (AMD) is the leading cause of blindness in the developed world for patients 60 years of age or older. It is projected to affect 196 million people worldwide by 2020. The macula is the central portion of the retina in the back of the eye. The photoreceptors in the macula are responsible tasks that require our central vision, such as reading and driving.

In patients with a genetic predisposition, changes in the macula develop over time that result in structural damage and visual changes. Some of these changes are reversible while other features lack any approved treatment, although researchers are working diligently on a multitude of approaches to treat the variety of structural changes that cause vision loss.

Which type of macular degeneration is "the good kind"?

There are two main categories of macular degeneration: dry and wet. Approximately 90% of patients with AMD have the dry form, which is traditionally considered to be the good kind of AMD because it confers less vision loss than the wet form in most cases. In the early and intermediate stages of dry macular degeneration, yellow subretinal deposits (drusen) are seen as in the photos above. These deposits cause no meaningful loss of vision until after many years they can coalesce and enlarge, resulting small blind spots and missing portions of central vision.

The much more serious form of macular degeneration is the wet form, where abnormal blood vessels grow beneath the retina. When these vessels bleed or leak other fluids into and underneath the retina, it causes sudden onset of vision loss and distortion. In patients with intermediate or advanced dry AMD, home monitoring with an amsler grid as in the images below is recommended. A new distortion of lines on the grid can indicate a conversion from dry to wet, as bleeding and leakage from new blood vessels underneath the retina can distort the tissues in the eye that receive and process light.

Why is my vision so poor even though I have dry macular degeneration?

Not all cases of dry macular degeneration are benign. After years to decades of progression, the advanced stages of dry macular degeneration result in damaged areas are so large that they cause loss of the entirety of a patient's central vision. The area in this case is referred to as "geographic atrophy" which is essentially scar tissue underneath the retina that causes loss of the photoreceptors above it.