How Age-Related Macular Degeneration and CNVM Affect the Layers of the Retina
Retina Cell Structure
Age-related macular degeneration, sometimes called AMD or ARMD, is a disease that not only destroys vision, but lives as well. Many patients with this disease suffer from depression and disconnection from family because they can no longer see the faces of loved ones.
This disease affects the macula, which is the area of the retina that allows us to read, work on a computer, crochet or knit, and see facial features, among other activities that involve central vision.
Peripheral vision remains untouched, so the patient never goes completely blind. AMD is caused by the aging process. As we get older, hyaline deposits, known as drusen, form under the retinal pigment epithelium (RPE) layer (the layer that focuses images) in what’s called Bruch’s membrane. Bruch’s membrane separates the choroid layer, the layer that provides the blood vessels for the retina, from the RPE layer.
Some Quick Biochemistry
The RPE layer deserves a bit of explanation. It has many functions, but the one that pertains to AMD is phagocytosis. Phagocytosis is a type of endocytosis.
Endocytosis is, essentially, a process of taking out the cellular garbage. Specifically, in the macula, the RPE layer is in charge of “sanitation.” It removes free radicals, dead cells, and other foreign materials from the layer below it, known as the choroid. The immune cells, called leukocytes, are the “sanitation engineers” in our garbage analogy. They are white blood cells that perform the necessary functions of phagocytosis.
What AMD Does: The CNVM
In the dry form of AMD, one theory is the immune system mistakes retinal cells for foreign bodies, or dead cells, and attacks and destroys them, leaving the free radicals and dead cells to collect into solid deposits, or drusen.
All of us will have some drusen at some point in our future, and most of the time it won’t affect the vision. However, in AMD there are many drusen deposits, and it causes a separation between the RPE layer and the blood vessels in the choroid. This separation will force new blood vessels to grow, in order to accommodate the lack of blood flow caused by the separation. This is called a choroidal neovascular membrane, or CNVM.
Unfortunately, these blood vessels tend to be frail and they break down and start to leak blood into the space between the RPE and choroid layers. This is when dry AMD converts to wet AMD. Wet refers to the bleeds caused by the new vessels.
Drusen in Macular Degeneration
Testing and Detection
New technology has made it easier for ophthalmologists to detect AMD earlier. The advent of optical coherence tomography, or OCT, scanners was paramount in facilitating detection. These scanners show a cross section of the retinal layers making it easy to see any abnormalities before they cause significant damage (see photo).
Fluorescein angiograms are still the gold standard for detecting wet AMD. A yellow dye, fluorescein, is injected into the patients are and pictures are taken at specific intervals with a special filter on the camera. The images are in black and white and are used to see bleeding from frail vessels (see photo).
Wet AMD does have treatments. I was lucky enough to work for a retinal specialist for over a year, who really knew the research on why the drugs worked. He was a complete jerk, and had absolutely no integrity, but he knew the science.
The main drug therapies available are Avastin (Bevacizumab), Macugen (Pegaptanib Sodium), and Lucentis (Ranibizumab). Lucentis is the most expensive, and is fairly effective, as is Macugen. Avastin, however, shows the most promise and is the cheapest of the three.
Avastin was originally developed by Genentech as an anti-cancer drug. In cancerous tumors, a similar phenomenon occurs. In order for the tumor to keep growing, it needs a blood supply. So, the vascular endothelial growth factor, or VEGF, protein is activated and new blood vessels are formed to feed the tumor. Avastin, Lucentis, and Macugen all inhibit this response. In AMD, this usually halts further deterioration and in some cases reverses the damage already done.
How the Drugs Are Administered and Their Results
These drugs are administered by an ophthalmologist, usually a retinal specialist, in the office. Unfortunately, it’s done by an injection into the eyeball itself. The eye is properly anesthetized first, but there is usually some discomfort after the procedure which mainly comes from the anesthetic.
The numbing gel causes the eye to become quite dry and this can last for several days after the injection. The only real treatment is artificial tears. I told my patients to use tears every hour once they arrived home until they went to bed. This would help rinse the excess numbing medication out of the eye and alleviate discomfort.
The results of these drugs are amazing. I’ve seen patients go from 20/400 to 20/25 after one treatment. This kind of improvement is rare; most patients see improvement of about three or four lines on the vision chart, but for these people, any improvement is greatly appreciated.
The majority of these patients were avid readers, or did quite a bit of work up close and since their diagnosis, they’ve been unable to do things they used to enjoy. So many patients have told me that listening to an audiobook is just not the same, and they terribly miss being able to pick up a book and read for hours.
Vitamins have shown great promise in the protection against the development of the disease and are the only treatment available for dry AMD. Ocuvite and Preservision, both made by Bausch and Lomb, are the leading vitamins on the market for the disease. They are also the most widely recommended by ophthalmologists.
The vitamin formula is known as the Age-Related Eye Disease Study, or AREDS, and it contains vitamin A, vitamin C, lutein, vitamin E, zinc and copper.
There is a new version of the vitamins called the AREDS 2 formula, which is part of an ongoing study set to be finished in 2013. This formula is a bit different. It eliminates the vitamin A, and adds zeaxanthin (pronounced “z-a-zan-thin”), and the Omega-3 compounds DHA and EPA.
The study is attempting to determine if reducing the amount of zinc, and eliminating vitamin A, while adding the Omega-3’s and zeaxanthin will change the effects the vitamins have on the disease. Vitamin A was eliminated mainly because smokers can’t take the supplement due to the increased risk for lung cancer it may cause.
The earlier the vitamins are started, the better. Antioxidants are the primary compounds that prevent and halt AMD. Vitamins are a good source, but diet is better. A diet rich in leafy green vegetables, nuts, and fish will supply the same vitamins and minerals found in the AREDS vitamins and they will be all natural making them easier for the body to absorb.
The Amsler Grid
AMD needs to be caught in its earliest stages to prevent damage. It is recommended that patients who may be predisposed monitor their vision at home using an Amsler grid (see photo).
People who may have a predisposition include those who have been exposed to excessive sunlight without the protection of sunglasses, smokers, those with a family history, those with hypertension, diabetes or who have a high fat intake, and Caucasians.
The Amsler grid should be used by these individuals daily in order to catch any changes immediately. The grid is held at 14 inches with glasses. The patient looks through their bifocal (if they have bifocals) and covers one eye. While looking at the small black dot in the center of the grid, the patient needs to observe if the lines of the grid around the dot are missing, wavy, or distorted in any way.
It is important to look only at the central dot and to not move the eye as movement may cause a false distortion. The patient then tests the other eye the same way. If changes are noticed, you should call your ophthalmologist immediately.
AMD is a devastating disease, and it can easily ruin quality of life. There are treatments, but the key is prevention and to catch the disease in its earliest stage. Always wear sunglasses ANYTIME you go outdoors (even if it’s a cloudy day); eat a diet rich in leafy green vegetables, nuts, and fish, or take vitamins; don’t smoke; and after the age of 45, check your vision with an Amsler grid at least once a week. If you notice any changes in your vision, either with or without the Amsler grid, you should contact your ophthalmologist right away.
Questions & Answers
© 2012 Melissa Flagg COA OSC