Protecting Your Vision: Diabetes and Eye Health

According to research published in JAMA Ophthalmology in 2023, 26.43% of people with diabetes had diabetic retinopathy (a disorder that causes vision loss) and 5% were at risk of losing their sight because of it.

Evidence also suggests that vision loss and blindness are three times more likely in people with diabetes.

Learning how diabetes causes vision loss, the most vulnerable population to diabetic retinopathy, and ways to care for your eye health can prevent this complication from arising.

Consistently high levels of blood sugar can create blockages and damage the blood vessels in the light-sensitive layer of tissue in back of the eyes, which is called the retina. Over time, this can cause the following conditions:

• Macular Edema : Happens when leaky blood vessels cause the macula (the center of the retina) to swell, which leads to blurry vision.

• Vitreous Hemorrhage : Occurs when blood leaks through damaged vessels into the eye or when the retina tears away from its underlying layer.

• Neovascular Glaucoma : High eye pressure caused by abnormal blood vessels growing where they don’t belong, which causes blockage of the retinal vein. This can lead to blindness.

• Cataracts : Clouding on the lens of the eye, which leads to blurry vision. It occurs because glucose enters the lens and is converted into sorbitol (a sugary alcohol), which absorbs water and swells the lens up.

All of these conditions — except cataracts — occur as part of a condition we call diabetic retinopathy .

Diabetic retinopathy (DR) occurs when high levels of sugar damage or block the blood vessels in the retina . This causes the retina to develop new vessels quickly and inefficiently, which often leak or bleed, leading to the development of diabetic macular edema, hemorrhage, and neovascular glaucoma.

It has two types:

1. Non-Proliferative Diabetic Retinopathy (NPDR): This is an early stage of DR and is characterized by leaky vessels that cause retinal swelling and blood vessel blockage in the retina. This can stop blood from reaching the macula and lead to blurry vision.

2. Proliferative Diabetic Retinopathy (PDR): This happens when the retina begins to grow new but fragile blood vessels. These often bleed and can cause you to see floaters or block your vision entirely.
   
   PDR also causes the development of scar tissue that can lead to retinal detachment, where the retina detaches from its underlying later. Patients with retinal detachment experience a “curtain falling over their vision”.

If left untreated, NPDR and PDR can cause the death of the retina, which leads to complete vision loss that cannot be reversed.

Diabetic retinopathy often doesn’t have any symptoms at the NPDR stage. But as it advances, patients show the following signs:

• Large, uneven red blots in the eye (hemorrhages)

• Small, round dots in the white of the eye (microaneurysms)

• Thick and thin veins (venous beading)

• Blood vessels that go nowhere in the retina

PDR has signs similar to NPDR. However, it’s also characterized by:

• New vessel growth on the back of the eye

• Retinal and vitreous hemorrhages

• Scar tissue development

• Retinal detachment

This can lead to blurred vision, floaters, photopsia (sudden but brief light flashes), scotoma (a loss of part of the vision), and sudden, painless complete vision loss.

A visual acuity test measures how well you can see the letters on a standardized wall chart or card that’s typically 20 feet (6 meters) away. It helps with early testing and detection of DR-caused vision problems.

This test typically requires the following:

• Optotype chart (Snellen, Allen, LogMAR)

• Flashlight

• Occluder card

• Corrective lenses

If your doctor uses a Snellen chart, they may ask you to read from the chart, cover your “good” eye to test your vision, read the letters backward, or push the chart closer if you find it difficult to read.

An ophthalmoscopy is an eye test that helps your doctor look at the retina, blood vessels, and the optic disk at the back of your eye. It enables them to spot any DR signs and provide treatment before they worsen.

Your doctor will dilate your pupils using specialized eye drops. This will make them larger and more sensitive to light. It may also cause your vision to become blurry.

Once your pupils are dilated, they’ll examine the back of your eye through either a slit-lamp, indirect, or direct examination.

An optical coherence tomography (OCT) is an imaging test that uses reflected light to take pictures of your retina. It helps your eye doctor see every retinal layer and allows them to understand whether they’ve been affected by DR.

Before starting the test, your healthcare provider will use eye drops to dilate your pupils. After that, they’ll examine your eyes using an OCT machine, which takes about five to ten minutes. Your eyes may remain sensitive to light for a few hours after the procedure.

A slit lamp biomicroscopy is an eye exam that helps doctors look at all the structures within your eyes, such as your pupils and retina, and find abnormalities.

Your doctor will use eye drops to dilate your pupils. They may also administer fluorescein dye to your eyes during this test, which makes everything easier to see.

Once your pupils are dilated, they will use a slit lamp to shine a beam of light into your eyes. This will help them visualize the inner structures of your eyes and find any changes.

A fluorescein angiography is an imaging test that uses a fluorescent dye to visualize the blood vessels in the retina. It helps doctors locate DR-caused blood flow and vessel abnormalities in the retina.

The test starts with your doctor administering eye drops to your eyes. After that, they’ll use an angiography machine to take pictures of your inner eye.

Once that’s done, they’ll inject a fluorescent dye into your arm and continue taking more pictures. This dye will help them notice changes like blockages or leads they may have skipped over.

Tonometry is a test that measures the pressure inside your eye to determine if you have glaucoma (increased eye pressure).

Before beginning the test, your healthcare provider will administer numbing eye drops to your eye. These will make sure you don’t feel pain during the test.

Once your eyes are numb, your doctor will introduce orange dye to the surface of your eyes and then examine them using a tonometer probe that flattens your cornea to test the pressure.

An optical coherence tomography angiography (OCT-A) is an imaging test that uses light to take 2D images of the retina. It helps to visualize the blood flow and structures of the vitreous, retina, and choroid sections of the eye.

OCT-A can also help doctors examine capillaries as small as 8 μm, helping them better locate any abnormalities present. It doesn’t require dye injection, making it more attractive for some patients than other eye tests.

If your DR hasn’t progressed far or at all, your doctor might recommend diabetes, blood pressure, and cholesterol medications to reduce your risk of eye complications.

They may also ask you to follow a specific diet to keep the blood vessels in your eyes healthy, such as a low-carb or keto diet.

Anti-VEGF drugs slow abnormal growth of new blood vessels, reduce the swelling of the macula (caused by leaky capillaries), and slow down vision loss. They’re usually given to patients with early-stage non-proliferative diabetic retinopathy (NPDR).

Some anti-VEGFs include:

• Lucentis

• Avastin

• Eylea

All of these have to be injected into the eye.

Steroids reduce inflammation , improve visual sharpness in patients with macular swelling, and synergize with the effects of anti-VEGFs .

Three steroids are currently used to treat DR. They include:

• Dexamethasone

• Fluocinolone

• Triamcinolone

However, steroids may not be as effective as laser treatment and may also increase eye pressure, making them unsuitable for patients with glaucoma.

Pan-retinal photocoagulation (PRP), or scatter laser, is the first-line treatment for early-stage proliferative diabetic retinopathy (PDR). It stops the abnormal growth of blood vessels via laser beams.

Scatter lasers have been shown to reduce severe vision loss by 50% in patients with abnormal vessel growth.

An eye surgery, or vitrectomy, is an invasive surgical procedure in which your doctor removes any structure causing visual impairment. 

This includes:

• Scar tissue that’s pulling the retina

• Blood and other fluids obscuring your vision

• Parts of or all of the cloudy vitreous

• Foreign objects present in the eye

Your surgeon may also use a laser to repair your retina during the surgery if it has pulled away from the eye wall. A vitrectomy is typically recommended for people with severe PDR and causes vision improvement in 90% of the patients who undergo it.

Your glycated hemoglobin (HbA1c) shows the amount of glucose in your blood over the past three months. If it’s more than or equal to 6.8% (51 mmol/mol), it can increase your risk of having diabetic retinopathy.

In fact, people with an HbA1C of 6.6% (49 mmol/mol) are highly likely to have DR, which increases their risk of vision loss.

This means it’s essential to regularly monitor your blood sugar levels to ensure they are under control. You can use non-invasive glucose monitoring if the traditional method is too uncomfortable.

Having blood pressure higher than 120/80 mmHg can increase your risk of DR by 10% to 20% , even if you don’t have hypertension. This is because high blood pressure can weaken the already fragile capillaries in your eyes, increasing your risk of vision loss.

Diabetes patients often have high levels of low-density lipoproteins (LDL), also known as “bad” cholesterol.

LDL particles build up in the blood vessels, harden over time into plaque, and hamper blood flow into the eyes, stopping them from getting the nutrients they need, increasing the risk of DR.

This is why it’s a good idea to keep your total cholesterol levels as low as possible (at least below 230) through treatment. Your LDL levels should also be lower than 100 mg/dL, ideally lower than 60 mg/dL.

If you have been diagnosed with diabetes and are at risk of developing diabetic retinopathy, it’s crucial to regularly take your medicines to lower blood pressure, blood sugar, and cholesterol — all of which contribute to an increased risk of DR.

Some medicines your doctor might recommend if you’re at risk include:

• Statins and fibrates (cholesterol)

• Beta-blockers and blood thinners (blood pressure)

• Insulin and glucose-controlling drugs (blood sugar)

Chronic stress can lead to a higher risk of high blood pressure . It may also lead to an elevation in your cortisol (stress hormone) level, which can increase your chances of having diabetes and high cholesterol — both of which contribute to DR.

Reducing stressors may include sleeping at least seven hours at night, moving around more, eating healthy food, and limiting social media usage. It’s also important to educate yourself on the kind of lifestyle that leads to diabetes , so you can avoid it.

To protect your vision from the effects of diabetic retinopathy, it’s important to get regular eye appointments as well as control your blood sugar.

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