If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:13:21

Video transcript

- Did you know that diabetes is the most common cause of blindness in individuals from the ages of 25 to 65? And blindness can be caused by multiple different complications associated with diabetes including glaucoma and cataracts, however in this tutorial, let's discuss the most common cause of blindness due to diabetes which is a condition known as diabetic retinopathy. And if we break down the term, we can receive generally, an understanding of what this disease is, so you have retino here meaning the retina, and pathy meaning disease. So, diabetic retinopathy is a disease of the retina that's caused by diabetes. And to describe what the retina is, let's bring in a diagram of the eye and go through some of the structures as it will help us as we learn more about this condition. Over here on the left, we have a cross-section of the eye and there's a few important structures to note. So this is the front of the eye here, and this is the back of the eye, and this part right here is known as the cornea. And it is where light initially passes through as it goes through the eye, and then it hits this structure right here, which is known as the lens. And the lens focuses the light on this structure in the back of the eye, this kind of brownish structure, and this is the retina. And then exiting the back of the eye here, this is the optic nerve. Then, you can also see all of these blood vessels that are traveling through the retina and then exit the back of the eye in the middle of the optic nerve. So if you look over here on the right, this is a front view of the eye. So this is kind of what it looks like when a doctor looks in to your eye. So here, right here we have what's called the optic disc, and the optic disc is really just the convergence of the retina and where it exits the eye, so this is really actually the optic nerve exiting the back of the eye. And then over here, you have a structure called the fovea. And the fovea is the portion of the retina with the highest density of cones which are the nervous receptors that correspond with color and more high resolution. So this is the portion of the retina that produces the highest resolution image. So, in a sense, you can kind of think of the fovea as producing an HD or a high definition quality image whereas kind of the more periphery of the retina on the outside will produce a much lower quality image. Now that we have a very basic general orientation to the eye and the retina, let's use this drawing to discuss the three stages of diabetic retinopathy. And they are, diabetes without retinopathy, non or pre-proliferative diabetic retinopathy, and proliferative diabetic retinopathy. And one thing that's important to note is that these stages of diabetic retinopathy are defined by their pathology. Not by the clinical presentation or their symptoms. But before we dive in to the pathology here, what are some of the common symptoms of diabetic retinopathy? Well, since it's a disease of the retina caused by diabetes, it makes sense that the symptoms are typically visual. And most of the symptoms tend to be fairly mild initially. They are things like blurry vision, or seeing dark spots or floaters. However, sometimes the symptoms can be very serious. Such as sudden onset of blindness. All right, so now let's get back to these stages of diabetic retinopathy. So the first stage I'm mentioned is diabetes without retinopathy. So why do we consider diabetes without retinopathy a stage of diabetic retinopathy? It doesn't quite make sense. And this is because the stages are dictated by the underlying pathology. And so, long before someone with diabetes develops vision changes, the underlying hyperglycemia or high blood sugar levels in their blood causes damage to cells known as pericytes within the retina. So these retinal pericytes are specialized contractile cells that surround the retinal vasculature here. And they're very important for helping regulate blood flow throughout the retina. And the damage to these pericytes is believed to be caused by an inability to properly metabolize the glucose within these cells. And then this results in osmotic damage. Now this damage to the retinal pericytes is the earliest stage of diabetic retinopathy and it's likely present in many, if not most individuals who have had diabetes for at least a few years, however, unfortunately this damage is only detectable under a microscope and therefore the retina on opthamologic or on an eye exam looks normal. It looks something like this. So therefore, early in the course of diabetes individuals will not necessarily have visual disturbances or signs of disease on exam, however this does not necessarily mean that the damage is not occurring, it's just not detectable. And the next stage of diabetic retinopathy is that of the non or pre-proliferative diabetic retinopathy. So recall that I just mentioned that these retinal pericytes help regulate blood flow through the vessels throughout the retina, and when they're damaged this results in the weakening of the capillary walls, as well as increased blood flow. What happens when these capillaries are damaged, it allows for the formation of microaneurysms which are focal dilations of weakened vessel walls and since these aneurysms occur in the microvasculature of the retina the vessels themselves are very small and not visible on opthamologic exam however, the microaneurysms are. And so they kind of look like these red dots that just appear kind of randomly throughout the retina. And if we bring in an actual picture here of the retina you can see that this is actually what they look like under examination. So they're a little bit harder to see, but they're these dots right here, right here, and here, which are typically the first clinical sign of diabetic retinopathy. However, this isn't the only clinical finding for this non or pre-proliferative diabetic retinopathy stage. In addition to damaging the retinal capillaries this loss or damage to the retinal pericytes also results in increased vascular permeability. and basically what this means is that the capillaries become leaky. Now this leakiness allows for large molecules such as proteins and lipids that are normally retained within the vessels to leak out in to this retinal tissue, and unfortunately, there isn't a normal mechanism to allow these to be reabsorbed. So as you can imagine, if proteins and lipids were to leak out, they get trapped. And this also can be seen under a dilated eye exam and it kind of appears as these yellow-white flecks on the retina, as you can see here. And this finding is known as a hard exudate. And, once again, even though this is just a drawing of the retina, it's actually fairly representative of what actual hard exudates look like. So you can see once again all of these microhemorrhages or microaneurysms in the retina, and then these white-yellow flecks all over and that's the proteins and lipids that have leaked out to form these hard exudates in the retina. So these two clinical findings are very characteristic of this second stage or the non or pre-proliferative stage of diabetic retinopathy. And because diabetic retinopathy is categorized by the pathologic findings and not necessarily the clinical presentation, this stage of diabetic retinopathy may or may not be symptomatic, so it usually begins about 15 to 25 years after someone's initially diagnosed with diabetes and it can last for many years before it progresses to the next stage which is proliferative diabetic retinopathy. Now, proliferative diabetic retinopathy can be asymptomatic, however, it's pretty uncommon so most individuals that reach this stage of diabetic retinopathy usually will have at least blurry vision or the presence of floaters. And as its name suggests, proliferative diabetic retinopathy is characterized by vascular proliferation within the retina. And the reason for this is that all of the microvascular damage that occurs in these first two stages of diabetic retinopathy results in something called ischemia. And what ischemia is, is a lack of oxygen supply to the cells of the retina. So, what the retina will do is it tries to compensate for this ischemia by producing a growth factor known as VEGF which stands for vascular endothelial growth factor. And VEGF does exactly what its name suggests. It produces new blood vessels. However, these blood vessels in diabetic retinopathy are abnormal, and the retina is not able to compensate for the ischemia. So it looks something like this over time. So you can see there's all of these new blood vessels that have formed within the retina and similar to the microaneurysms and the hard exudites, this vascular proliferation can also be identified on a dilated eye exam. And it looks something like this. So you can see some maybe a little bit more normal, larger vessels in the retina, but then throughout here, are these little bit lighter kind of squiggly looking newer vessels. So this is that vascular proliferation that is indicative of the proliferative diabetic retinopathy. And unfortunately, once diabetic retinopathy hits this third stage and becomes proliferative the clinical course is pretty unpredictable and it can actually be fairly severe, resulting in potentially vision threatening complications such as vitreous hemorrhage or retinal detachment. So now that we have a better understanding of the pathological mechanisms of diabetic retinopathy, how can we use this information to learn how the condition is treated? Well, first off the treatments are aimed at halting the underlying pathologic mechanisms of diabetic retinopathy, however their use is more commonly dictated by the severity of symptoms. So we'll start with the first stage the diabetes without retinopathy, and since the pathologic mechanism of diabetic retinopathy is directly related to the underlying hyperglycemia associated with diabetes, the best way to prevent or delay the progression of diabetic retinopathy is early and aggressive control of one's blood sugar with lifestyle modifications and anti-diabetic medications. However, oftentimes this is not enough, and over time even individuals with very well controlled diabetes may develop diabetic retinopathy. So because these early stages are often asymptomatic, it's also important for all individuals with diabetes to have a yearly dilated eye exam performed by an ophthalmologist to look for the signs of diabetic retinopathy. Now once an individual has signs of diabetic retinopathy such as the microhemorrhages or the microaneurysms and these hard exudites, and they move in to that second stage of diabetic retinopathy and now the treatment is dependent on symptoms. So if that individual is, say, asymptomatic their only treatment is still to just maintain proper blood glucose regulation and the yearly eye exam. However, as soon as symptoms such as blurry vision or floaters develop, then an individual with diabetic retinopathy should be placed on anti-VEGF medications. And these medications will prevent the proliferation of new blood vessels in the retina and therefore help prevent the progression to proliferative diabetic retinopathy. Now, unfortunately once someone has evidence of proliferative diabetic retinopathy with this vascular proliferation of the retina, the clinical course is actually pretty difficult to predict. So for this reason, anyone in this stage of diabetic retinopathy is recommended to undergo a procedure known as laser photocoagulation. And this is a process by which very precisely focused lasers are used to stop the growth of these vessels on the retina, and unfortunately this treatment is not necessarily curative it's more aimed at preventing serious complications of diabetic retinopathy such as retinal detachment where, as its name suggests, the retina can become detached from the posterior wall of the eye, or vitreous hemorrhage where these new blood vessels actually burst and bleed in to the inside of the eye. And both of these conditions, may potentially result in permanent blindness, therefore anyone with diabetes who develops sudden onset vision loss should be evaluated emergently to rule out these complications. So diabetic retinopathy is a disease of the retina that's caused by diabetes and it tends to be a slow progressive complication of diabetes that eventually affects nearly all individuals with diabetes maladies. However, the underlying mechanism of diabetic retinopathy is directly associated with glycemic control or blood glucose regulation. Therefore, like many of the complications of diabetes, proper treatment of the underlying condition can prevent or at least slow the progression of diabetic retinopathy.