The Unseen Link Between Diabetes and Retinal Diseases

Can you tell me what specific signs of diabetes are most commonly detected during an eye exam?
 

When an eye care provider is looking at the eye of someone with diabetes, they are looking at every single part of the eye to see if there's any changes that are perceptible. And lots of changes can happen.

The most common change occurs in the retina – the blood vessels in the retina start to develop microaneurysms and there is leakage of exudate, and we can even see cholesterol deposits in the eye. The reason that happens is because the blood vessels get damaged by high glucose and consequently become leaky. Secondly, because of this leakage, there can be hemorrhages.

These are all signs that the blood vessels are starting to become compromised. And once the blood vessels become compromised enough, that means oxygen and blood aren't getting to the end organs like they ought to, and the retina starts to become oxygen-deprived. The response of the retina to the deprivation of oxygen is to send a signal to the body to create new blood vessels, in areas of the retina where the native blood vessels have become completely compromised.

The other things that can happen anywhere in the body – but also in the eyes – is that diabetes can cause compromised healing. In diabetic patients, their cornea might become drier and lose sensation because the nerves have been damaged, resulting in neurotrophic keratitis. If patients have proliferative diabetic retinopathy, they can also develop blood vessels in the iris. They can also develop new blood vessels in the trabecular meshwork, which can cause glaucoma.

So, things will start off in an optometrist or comprehensive ophthalmologist’s chair, but they can quickly spiral and require a retina specialist, glaucoma specialist, or a cornea specialist.

What steps do you recommend a patient take if early signs of diabetic retinopathy are detected?
 

I think the great thing about being an ophthalmologist is, when someone has diabetes, often they may not be experiencing any other end-organ issues. But the visual sense is of course very important to people, and so if you tell them that they might lose their vision, it really gets them to act.

One of the first things I recommend to people to preserve their vision is to make sure they're actually in the healthcare system and have a primary care physician. I also like to make sure that the patients themselves are keeping track of their diabetes status. If you're not checking your blood sugar levels on a daily basis and if you don't know what your last A1C is, then you don't know how to adjust things appropriately.

What lifestyle changes might diabetic patients make to preserve their vision?
 

Patients need to be counselled about monitoring their diet, increasing exercise, etc. By improving exercise alone, some people with early-stage diabetes can dramatically improve their body's ability to handle glucose and decrease the insulin insensitivity that has developed.

However, this advice can be difficult to give to patients that don't necessarily have easy access to these things. For example, if they're working two jobs it's going to be hard to increase the amount of exercise they can fit into their daily routine. If they're living in a food desert, it's going to be very hard to counsel them about their diet.

In instances like these, I realize my limited role as an eye doctor. That’s why having a good primary care doctor who can help the patient to access resources is really important.

How do your recommendations differ for pediatric and adult patients?
 

This is going to change as rates of childhood obesity increase in our country, but for the most part, the pediatric patients I examine have type 1 diabetes; older patients tend to have type 2.

Type 1 diabetes is a little trickier to handle because the body is simply not going to produce any insulin; you're not going to be able to improve your body's ability to metabolize glucose because you are dependent on exogenous insulin for that.

With pediatric patients, initially their parents are responsible for making sure that they see their pediatrician, see their endocrinologist, and take their medication. But when these children become teenagers, they must go on their own journey and take ownership of managing their condition.

Call it teenage rebellion, but because of the emotional turbulence of puberty or because of the difficulties of adjusting to high school, college, etc., a number of young adults I see lose control of their type 1 diabetes and develop severe retinal damage that impacts them for the rest of their adult life. At a certain point, you can't get back what you've lost. It’s really important to develop a therapeutic alliance with these patients early on and get them to understand that taking ownership of this disease means taking responsibility for how they are going to function for the rest of their life.

How might the risk of glaucoma developing from diabetes be monitored?
 

The glaucoma/diabetes connection is quite complex. First there is neovascular glaucoma, which is a bit more straightforward. Essentially, the eyes become starved of oxygen, new blood vessels form, and these new blood vessels grow in areas that they're not supposed to, including the trabecular meshwork. Neovascular glaucoma must be managed procedurally – these patients will need injections to get rid of those blood vessels, and they'll need surgery.

A slightly more nuanced link is the underlying increase in risk for open-angle glaucoma in people who have diabetes. Large-scale studies show a possible link between higher pressure – which leads to glaucoma – and having diabetes. Other studies have shown that people with diabetes may be more likely to have glaucoma (1). We don't know the exact pathophysiology of this, but it's important for me, when I see someone with diabetes, to make sure that I'm looking for signs of glaucoma.

Are we any closer to understanding how diabetes might be linked to glaucoma?
 

We don't fully understand it, but I think it has to do with how overall health improves our ability to manage different diseases. We’re also realizing that diabetes is not just a sugar/blood vessel problem, it's a neurological disease. We are starting to appreciate how diabetes damages our neurons progressively, which is surprising as we don’t traditionally think of diabetes damaging the body like neurodegenerative diseases such as Alzheimer's disease. There are remarkable people – such as Elliott Sohn, Professor of Ophthalmology and Visual Sciences at the University of Iowa – who are currently investigating how diabetes may not be just a vascular disease, but a neurovascular disease. This type of research will be important for understanding diabetes as a whole.

Ophthalmologists can look directly in the eye, which helps us to visualize neurological damage from diabetes in a way that other specialists do not have easy access to. When I look at someone's retina and I see severe diabetic retinal damage, I know that's also what their brain looks like, what their liver may look like, what their nerves may look like.

One of the best things about being a retinal specialist is the variety of tools we have for managing conditions like diabetic retinopathy, which can really help to save people's vision. These tools also help us to understand diabetes at a level that can be beneficial for other practitioners as well.