Diabetic Retinopathy: Causes and Diagnosis

Diabetic retinopathy is an eye condition that is a complication of diabetes. It is strongly associated with the duration of diabetes, status of retinopathy at diagnosis, and level of glycemic control. Other factors associated with the disease include hypertension (high blood pressure), nephropathy (kidney disease), and dyslipidemia.

Diabetic retinopathy is diagnosed using a comprehensive dilated eye exam by an ophthalmologist or optometrist who has experience with diabetic eye disease. Early detection and treatment can reduce complications and reduce the progression of the disease.

Causes of Diabetic Retinopathy

The most common causes of diabetic retinopathy include chronically elevated blood sugar (hyperglycemia), duration of diabetes, and blood pressure levels.

Hyperglycemia

Elevated blood sugars occur in people with diabetes for a variety of reasons, including inadequate medication (timing, dosing, expense), difficulty in self-management, poor diet, or excessive carbohydrate consumption, to name a few.

When sugar (glucose) cannot be taken into the cells to use for energy, the excess remains in the blood and can cause damage to the body.

Diabetic retinopathy occurs when the tiny vessels in the retina become damaged from excess sugar. An accumulation of sugar causes a disruption in the vessels' ability to transport blood and nutrients to the optic nerve.

This vessel blockage can result in balloon-like pockets that leak fluid and blood into the retina, which can result in macular edema. The macula is the part of the eye that helps with focusing. When it becomes filled with fluid, vision can become blurry.

If too many vessels are affected and become closed off, the body will compensate by growing new, weaker blood vessels. When this happens, diabetic retinopathy is referred to as proliferative retinopathy, a more advanced stage of the disease.

The new blood vessels continue to leak fluid and blood, and can also cause scar tissue to develop. A buildup of scar tissue may cause retinal detachment.

Duration of Diabetes

Retinopathy can occur even before a diabetes diagnosis. And the longer you have diabetes, the more likely you are to develop retinopathy.

But there is good news. Many people will not have symptoms of diabetic retinopathy and the more severe form, which can cause vision loss, is very rare. This is especially true today due to early detection and better treatment options.

The American Diabetes Association recommends that all people with diabetes get a dilated eye exam. Adults with type 1 diabetes should have an initial dilated eye exam within five years after onset of diabetes and people with type 2 diabetes at the time of diagnosis.

Elevated Blood Pressure

There is an association between blood pressure control and diabetic retinopathy. Some studies suggest that elevated blood pressure can increase the risk of diabetic retinopathy as well as disease progression. It is hypothesized that elevated blood pressure can damage the retinal capillary endothelial cells.

Nephropathy

People with diabetes who also have nephropathy (kidney disease) are more likely to develop diabetic retinopathy. In patients with type 1 diabetes, it is well established that retinopathy precedes nephropathy. However, this relationship is less well known in type 2 diabetes. Some studies have shown that nephropathy precedes retinopathy.

Pregnancy and Puberty

Pregnancy and puberty may accelerate diabetic retinopathy. With pre-existing type 1 or type 2 diabetes, this can occur when the pregnant person's blood sugars are not in good control at the time of conception.

Genetics

Some people with diabetes may have a genetic predisposition to developing diabetic retinopathy. Researchers have identified about 65 genes that are associated with the disease. These genes play roles in insulin signaling, angiogenesis (the process through which new blood vessels form), inflammation, neurogenesis, and regulation of endothelial cells.

Cardiovascular Risk Factors

Certain cardiovascular risk factors are associated with retinopathy and can contribute to the cause.

Abnormal Lipids

Elevated lipids, also referred to as dyslipidemia, have been associated with diabetic retinopathy. Specifically, dyslipidemia is known to cause hard exudates, which occurs when the vessels in the eyes leak lipids into the retina. People with type 2 diabetes and hyperlipidemia seem to have an increased risk of developing diabetic macular edema.

Metabolic Syndrome

Researchers have discovered a correlation between the development of diabetic retinopathy and metabolic syndrome. Metabolic syndrome is characterized by central obesity, hyperlipidemia, insulin resistance, and hypertension. The mechanism by which this occurs is thought to be partly due to the body's state of chronic inflammation.

Lifestyle Risk Factors

Smoking exacerbates vascular damage in people with diabetes. A meta-analysis of the literature suggests that the risk of diabetic retinopathy is significantly increased in smokers with type 1 diabetes while significantly decreased in smokers with type 2 diabetes.

Despite the decrease in retinopathy in smokers with type 2 diabetes, smoking can contribute to the development of many other complications of diabetes and is not advised.

Diagnosis

All people with diabetes should receive a comprehensive dilated eye exam by an ophthalmologist or optometrist who knows how to treat eye disease in diabetes. For those with type 1 diabetes, this should happen within five years after the onset of diabetes. And for those with type 2 diabetes, this should occur shortly after diagnosis.

Further testing and follow-up will depend on whether or not retinopathy is present, if you have any symptoms, and your blood sugar control.

Self-Checks and At-Home Assessment

There is no way to self-check for diabetic retinopathy. And because most people do not even know they have it, they are less likely to be screened. It is especially important for all people with diabetes to have a dilated eye exam. Adequate and timely screening can prevent or delay disease development and progression.

Comprehensive Dilated Eye Exam

The American Diabetes Association reports that up to one-fifth of patients with type 2 diabetes have some sort of retinopathy at the time of diabetes diagnosis, especially if people newly diagnosed have had undiagnosed diabetes for many years.

Additionally, many people with retinopathy may not have symptoms and therefore adequate screening is essential to determine and treat retinopathy before it progresses.

A comprehensive dilated eye exam dilates the eyes using drops so that the retina can be seen. The drops make the pupil (black part of the eye) bigger to expand the view of the retina. Next, the healthcare provider will shine a bright light (slit lamp) into the pupil to see into the retina.

If retinopathy is found, you may need to go for more testing. This test can also be used to diagnose diabetic macular edema, glaucoma, and cataracts—common eye diseases associated with diabetes.

Indirect Ophthalmoscopy

In this exam, the examiner wears an optical instrument on the top of their head that contains special lenses that magnify the eye. The lenses and lights allow the examiner to see more retinal detail.

Optical Coherence Tomography

Optical coherence tomography (OCT) is often used to examine disorders of the optic nerve such as diabetic macular edema (DME) and glaucoma. It is thought to be one of the best tests for diagnosing and evaluating DME and can also be used to monitor responses to treatment associated with DME such as anti-VEGF injections.

It is a non-invasive test that uses light waves to assess a cross-section of your retina and measures its thickness. The OCT machine scans your eyes without touching them. The exam usually takes five to 10 minutes.

Fluorescein Angiography

This test is used to see if there are any leaks or microaneurysms in the vessels of the retina. It is also used to track changes in the eye and target treatment areas. This test is done by dilating the eye and then infusing a dye into your vein. The dye lights up the small vessels in the eye. When the dye is active, your healthcare provider will take pictures of your eye.

Your eyes may be sensitive to light after the test, and your skin could be tinted yellow. In rare instances, you could have an allergic reaction to the dye. If you have any signs of an allergic reaction, such as itchiness, hives, or trouble breathing, you should let your healthcare provider know right away.

Digital Retinal Imaging

The American Diabetes Association says that retinal photographs have high potential as a resource for screening when high quality eye professionals are not readily available. These digital photos can take a picture of the retina, blood vessels, and optic nerve, and help to evaluate diabetic eye disease.

It should be noted that they do not substitute for a comprehensive eye exam but can be useful as an additional diagnostic tool, detecting most clinically significant diabetic retinopathy.

Labs

Assessing glycemic control can help professionals assess the risk of diabetic retinopathy and prevent progression of the disease.

The Diabetes Control and Complications Trial (DCCT) determined that intensive glycemic control in people with diabetes reduced the development or progression of diabetic retinopathy by 35% to 76%. Early treatment of elevated blood sugar and reductions in hemoglobin A1C have also been shown to reduce progression of retinopathy.

Therefore, your healthcare provider may want to evaluate your hemoglobin A1C (three-month average of blood sugar). Most people with diabetes should aim for a hemoglobin A1C of 7% or less, but targets should be individualized. If your A1C is above goal, a 10% reduction may help to reduce retinopathy progression.

Your healthcare provider can evaluate your hemoglobin A1C using a venous blood draw or finger stick (if they have a point-of-care A1C machine on-site).

Other laboratory markers may include a blood and urine collection to assess your kidney function, cholesterol, and triglyceride levels. Results that are abnormal will not be enough to diagnose retinopathy, but they could be an indication of an increased risk of disease.

A Word From Verywell

There are many causes that can attribute to diabetic retinopathy, some of which can be controlled. Optimization of blood glucose, blood pressure, and lipids; smoking cessation; and early detection and screening can prevent or delay the development and progression of diabetic retinopathy.

Improvements in diagnostic assessment tools can help to reveal asymptomatic disease and provide accurate assessment for treatment and prevention of serious complications.

If you have diabetes, the most important thing you can do to protect your eyes is strive for good blood sugar control and make sure you receive a comprehensive dilated eye exam. If you do not have a reputable eye doctor, ask your primary healthcare provider, endocrinologist, or certified diabetes care and education specialist for a recommendation.