In this particular episode of Ask an Eye Doc, you will learn:
- Four important layers of the eye
- The importance of photoreceptors
- How the photoreceptors are maintained
- Where drusen occur and how they can damage the retina
This episode will make more sense if you have already listened to the following episodes:
- episode 7 – what is the retina
For you readers out there, here’s the answer in written form:
Marci asks, “I have been recently diagnosed with retinal drusen. What are drusen?”
First of all, good grammar! Drusen is a plural word, just like oxen. If you only had one of them, it would be called a druse. Most people don’t have only one, so drusen is usually the word you hear.
Second of all, you’re going to hate me… this is a big question. If you really want to understand what drusen are, you’ll need a little course on the retina. Be sure to listen to episode 7 if you don’t already know what the retina is.
First, let’s discuss four different layers. The first two are the deepest layers of the retina, and the next two are layers behind the retina. They are (in order):
- Photoreceptors (deep in the retina)
- Retinal pigmented epithelium (the last layer of the retina)
- Bruch’s membrane (just behind the retina)
- The choroid (just behind Bruch’s membrane)
Rods & cones
Let’s start by reviewing photoreceptors. Remember from episode 7 that photoreceptors (rods & cones) are the microscopic nerve cells that detect light. When it comes to the retina, it’s all about saving your photoreceptors. If the photoreceptors die, you don’t see.
The next layer past the photoreceptors is a specialized layer of cells called the retinal pigmented epithelium (RPE). Think of the RPE as mothers to the photoreceptors. They feed them and change their diapers. Okay, so photoreceptors don’t have diapers, but they do have waste products that need to be removed in order for them to stay healthy & happy, and it’s the RPE’s job to take care of that.
Bruch’s membrane and the wild, wild choroid
The next layer past the RPE is Bruch’s membrane and then… the choroid! (I’ll talk about Bruch’s membrane in just a minute). But first, think of the choroid as a marketplace where food and waste are exchanged. The choroid is where the RPE goes “shopping” to get fresh nutrients and to get rid of waste products. The choroid is a dangerous place for photoreceptors, since it is not very highly regulated. There are a lot of loosely organized blood vessels and excess fluid.
The barrier: Bruch’s membrane
There is a tight barrier between the RPE and the choroid that prevents the disorder of the choroid from spilling over into the RPE and the photoreceptors. It’s called Bruch’s membrane.
Bruch’s membrane is a very tight, thin layer (only about 2-4 microns thick… that’s 2-4/1000ths of a millimeter!) Only the RPE has the ability to transport nutrients and waste products across Bruch’s membrane to and from the choroid.
Now that you’ve survived my mini-anatomy lesson, with cheesy analogies and all, let’s tackle your question about drusen!
Drusen are areas of damage to Bruch’s membrane and the RPE. If you have drusen, your optometrist can see them by looking into your eye with a microscope. They show up as little yellow dots.
If Bruch’s membrane breaks down, the RPE is no longer able to control what comes in from the choroid and what gets out. As a result, waste products accumulate and fluid leaks into the retina from the choroid. This leads to damaged photoreceptors. And remember, damaged photoreceptors means you don’t see!
What does this mean for Marci?
Obviously, Marci, you can still see. But not in those microscopic areas where your drusen have begun to accumulate. Depending on the size and location of the drusen in your eye, you may have an increased risk of developing macular degeneration. To learn more about macular degeneration, be sure to listen to episode 11.
If you have drusen in both eyes, for example, you have a 3-4% risk per year of developing choroidal neovascularization. “Neo-” means “new” and “vascularization” means blood vessel growth. So, “choroidal neovascularization” means new blood vessels growing in the choroid, which leads to macular degeneration.
Anywhere in the retina where the drusen get too big, they create a small area where the retina does not receive as many nutrients, including oxygen. At these larger areas of drusen, a small detachment of the retina can occur, leading to more retinal degeneration.
Hard drusen vs soft drusen
Drusen are classified as hard or soft. Your eye doctor can tell you what type you have based on their appearance. Hard drusen in the macula can coalesce, or clump together, into large patches and lead to atrophic macular degeneration, also known as “dry” macular degeneration.
Soft drusen look larger and fluffier. If you have five or more soft drusen in the macula, or if they are larger than 63 microns, you are more likely to develop exudative macular degeneration, also known as “wet” macular degeneration.
Now you know!
Hopefully, Marci, this gives you a better understanding of what drusen are. Make sure you follow up with your optometrist as he or she has recommended. It’s likely that only a yearly eye exam is necessary to monitor your retinal drusen, but it may warrant more frequent visits, depending on the level of drusen you have.
I know we talked about a lot today. If you have an additional question, go to askaneyedoc.com/question and feel free to leave me a voice message. I’ll be happy to do a follow-up episode.
Thanks for submitting your question!