This Is Your Brain on Wet AMD
Exactly what's going on with the wiring in your head when you have wet AMD? Get the details, here.
If you have wet age-related macular degeneration (AMD), or know someone that does, it can be a little confusing to understand what’s going on. The end result is obvious: You’re having trouble seeing. But what part of the body is responsible for vision loss from this progressive eye condition? Is it your eye? Your brain?
“In a way, your eye is a direct extension of your brain,” says Timothy G. Murray, M.D., past president of the American Society of Retina Specialists and a retina specialist in private practice in Miami, who explains that the eye is considered part of the central nervous system.
To understand, neurologically speaking, what happens when you have wet AMD, you need to understand the physiology of the disease and its progression—including how the eye communicates with the brain through the optic nerve and how your brain registers what you’re seeing (and what you no longer can). If this sounds a little daunting, stick with us. We asked our ophthalmology experts to break it down in an easy-to-understand way.
What Causes Wet AMD?
It all begins in the back of the eye, in the thin tissue layer called the retina. “Starting around the age of 60 or so, little deposits will build up underneath the retinal cells,” says Robert W. Wong, M.D., a retina specialist at Austin Retina Specialists and affiliate faculty, department of ophthalmology, at The University of Texas at Austin Dell Medical School in Austin, TX. “These retinal deposits are called drusen. These are basically the waste products of the retinal photoreceptor cells.”
Usually, your body naturally removes drusen twice a day—morning and night—from the retina. While they likely do not cause AMD, having large drusen increases your risk of AMD. And over time (as with so many things in our bodies), our metabolism slows down, Dr. Wong says. As it slows, drusen deposits aren’t regularly removed and accumulate. That accumulation typically happens in the very center of the retina called the macula and can cause mild distortion in vision—straight lines start to look a little wavy. Doctors refer to this condition as dry AMD, a precursor to what’s to come.
Dry AMD itself can progress over time, but that progression can take years. Wet AMD, in contrast, is a faster progressing but less common condition (only 10% to 15% of AMD cases are wet), potentially causing vision loss in a matter of months. With wet AMD, abnormal blood vessels grow where they shouldn’t, in the macula. They leak blood or fluid, causing scarring. They can impact area in the center of the macula called the fovea, which helps with the clearest, sharpest central vision.
Currently, there is no treatment for dry AMD (though a vitamin formulation called AREDS-II can help halt progression). But there is treatment for wet AMD, called anti-vascular endothelial growth factor (anti-VEGF) therapy, as well as a key monitoring tool known as optical coherence tomography (OCT), Dr. Murray says. “Anti-VEGF revolutionized care for these patients,” he says. At the same time, “imaging for early detection of conversion from dry to wet or documenting the status of wet neovascular AMD and response to treatment using OCT are two game changers for our patients.”
Wet AMD and Your Brain
So where does the brain fit into this picture? First, it’s important to know that it doesn’t appear that our brain causes wet AMD, says neuro-ophthalmologist Joshua Pasol, M.D., an associate professor of clinical ophthalmology at Bascom Palmer Eye Institute of the University of Miami Miller School of Medicine. Wet AMD appears to be only a retina-based condition.
Here’s what happens: Light goes through the front of your eye—the cornea, the pupil, and the lens—and when that light reaches the back of the eye—the retina—its photoreceptor cells turn it into electrical signals, which then travel through the eye’s optic nerve to the visual cortex in the brain. The visual cortex “scatters all that information to make sense of what the retina has brought to the brain,” Dr. Pasol explains. “That’s how we interpret vision—through our brain.” In fact, a whopping two-thirds of the brain is dedicated to the visual pathway.
Because wet AMD causes vision loss in the center of the eye, the brain compensates for this by telling you to tilt your head to see out the sides, or peripheral, parts of your eye. “Our occipital lobe in the brain that receives the visual information is aware that peripheral vision is working,” says Dr. Pasol. “So the frontal lobe, which controls your eye movement, takes over and says ‘OK, we have to get that peripheral vision into play.’”
Another way the brain can be involved is something called Charles Bonnet Syndrome)—visual hallucinations often experienced upon waking, says Dr. Wong. You can have this condition when you’ve lost significant vision from wet AMD (or any other eye condition with vision loss). The brain basically “fills in” the missing signals from the retina with images that it makes up. You might see people, scenes, animals, buildings, trees, or even dragons. The best way to know if you’re having visual hallucinations related to wet AMD is to talk with others, like family or your doctor.
Remember, although there’s no cure for wet AMD or issues related to it, with anti-VEGF treatment you can help stave off further visual loss from progression of the condition. Talk with your doctor or ophthalmologist if you are concerned about changes happening with your eyesight. The sooner you seek help, the quicker you can start treatment to preserve your vision.
All About Drusen: American Academy of Ophthalmology. (2021.) “What Are Drusen?” https://www.aao.org/eye-health/diseases/what-are-drusen
The Eye at Work: National Eye Institute. (2019.) “How the Eyes Work.” https://www.nei.nih.gov/learn-about-eye-health/healthy-vision/how-eyes-work
What You Might See with Charles Bonnet Syndrome: American Academy of Ophthalmology. (2020.) “What Is Charles Bonnet Syndrome?” https://www.aao.org/eye-health/diseases/what-is-charles-bonnet-syndrome
All About Charles Bonnet Syndrome: The Western Journal of Emergency Medicine. (2012.) “Visual Hallucinations: Charles Bonnet Syndrome.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3555593/
Anti-VEGF Therapy: The American Journal of Pathology. (2012.) “A Brief History of Anti-VEGF for the Treatment of Ocular Angiogenesis.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5691342/