My father is making us tea in his 70’s styled kitchen when I show him an image on my phone.
“What’s that?” he asks.
“They’re macular drusen, Dad. They are a sign of macular degeneration. This image is from my new paper that just got published,” I say.
“Good job Miss!” he replies. “They actually look quite pretty. How do they cause macular degeneration?”
What my father doesn’t realize is that this is one of the biggest outstanding questions that puzzle researchers in field of macular degeneration. We know that drusen are small, fatty deposits that form underneath the retina, the thin tissue that lines the back of the eye and allows us to see. We know if we see drusen in someone’s retina, it’s a likely sign they have early macular degeneration. We can even measure drusen and use this measurement to predict the chance someone will progress to a later stage of macular degeneration that causes blindness. But we still don’t know exactly why or if drusen actually cause macular degeneration, or more importantly how we can use our limited understanding of drusen to stop or treat the disease.
Recently, my own research team embarked on a project to better understand what drusen do in the retina over time. If we can understand the typical “lifecycle” of a drusen, perhaps we can better understand their role in macular degeneration and, ultimately, how to manage the disease.
What do we already know about the Drusen lifecycle?
Research indicates that drusen are quite dynamic. They emerge underneath the retina and can grow in height and diameter over time. They can also merge or coalesce with other nearby drusen to form ‘confluent’ drusen.
Interestingly, drusen can also shrink in size and disappear completely. Some researchers have shown that this regression is actually an ominous sign, and individuals with regression actually are more likely to have the disease progress to a worse stage rather than improve.
Many questions about this process remain unanswered. Why do drusen form in one part of the retina and not another? What happens to the retina above the drusen as they grow and shrink?
What our study found
We asked individuals with macular degeneration who visited the Centre for Eye Health* in Sydney, Australia if they would like to be part of our study. For those who agreed, we took images of their retinas and randomly selected up to eight different drusen across each retina. We then had the patients come in again a year or two later to investigate how their drusen changed.
What did we find? For drusen that grew in size, we found that they compressed the retinal layers above them. Specifically, they compressed the outer retina where photoreceptors are found (the neurons in the eye that detect light). This compression was directly proportional to the height of the drusen. For drusen that had shrunk, we found the retinal layers returned to normal thickness.
We also looked to see if we could predict when drusen were going to appear. To do this, we found drusen that were in the second set of images for study participants but not in the first set. We measured the retina and found that before drusen emerged, the retinal pigment epithelium (a layer of cells that nourish the photoreceptors) was thicker at this location.
What do these findings mean?
Our study confirms that drusen don’t just elevate the retina as they form; they actually push their way through the retina, disrupting important retinal neurons like photoreceptors. We know that in late macular degeneration where blindness occurs, photoreceptors die. It could be that drusen contribute to this process by stressing photoreceptor cells as they grow through them.
When drusen regressed, we didn’t see any permanent effects on the retina. It might be that we simply couldn’t detect changes that did occur with the type of images we took.
We have also possibly found a way to predict where a drusen is going to emerge. This is very exciting, because if we can study areas of the eye where drusen usually appear, we can figure out why some areas of the retina are more susceptible to damage than others. And maybe by doing this, the next time my dad asks how drusen cause macular degeneration, science will have an answer.
Editor’s Note: Age-related macular degeneration is the “leading cause of irreversible vision loss in people aged 50 and older in the developed world” (Retina, 2014). Risk factors including smoking, family history, increased BMI, hypertension, oxidative damage (like light exposure and reactive oxygen species generation) and aging. Worried about developing macular degeneration? There is some evidence that at-risk individuals may benefit from consuming foods rich in antioxidants or supplementing their diet with antioxidant vitamins. Inflammation, autophagy and mitochondrial dysfunction are also implicated in macular degeneration, pointing to metabolic interventions (balanced diets, plant-based diet, and potentially even intermittent fasting) being potentially beneficial for macular degeneration.
*The Centre for Eye Health is a joint initiative by the University of New South Wales and Guide Dogs NSW/ACT and provides advance eye imaging and diagnostic testing to individuals referred with low to moderate eye disease or are suspected of having eye disease free of charge.
