Diabetic Eye Disease: Diagnosis, Causes, and Symptoms

By Debra A. Sokol-McKay, MS, CDE, OTR/L, SCLV, Updated by Sefy Paulose, M.D., March 2022

Diagnosing Diabetic Eye Disease

Diabetic retinopathy usually has no early warning signs. It can be detected only through a comprehensive eye examination that looks for early signs of the disease, including:

Leaking blood vessels
Macular edema (swelling)
Pale, fatty deposits on the retina
Damaged nerve tissue
Any changes to the retinal blood vessels

To diagnose diabetic eye disease effectively, eye care specialists recommend a comprehensive diabetic eye examination that includes the following procedures:

Distance and near vision acuity tests
A dilated eye (or fundus) examination, which includes the use of an ophthalmoscope. In a dilated eye examination, it is the pupil that is dilated—not the entire eye. This allows the examiner to see through the pupil to the retina. Visual acuity tests alone are not sufficient to detect diabetic retinopathy in its early stages.
A tonometry test to measure fluid pressure inside the eye.
A fluorescein angiography test, if more serious retinal changes, such as macular edema, are suspected. Fluorescein angiography is an eye test that uses a special dye and camera to look at blood flow in the retina.
Optical coherence tomography (OCT) testing may be used to gain a clearer picture of the retina and its supporting layers. OCT is a type of medical imaging technology that produces high-resolution cross-sectional and three-dimensional images of the eye.
Also, an Amsler Grid test can detect early and sometimes subtle visual changes in a variety of macular diseases, including diabetic macular edema.

The first image below shows an Amsler Grid as seen with unimpaired vision. The next image gives an example of an abnormal Amsler Grid, as seen by a person with eye disease. These images of the grids are much smaller than normal size so that we can show them to you on this website. If you have been diagnosed with diabetic retinopathy or any eye disease, ask your eye care professional for a real Amsler Grid you can use at home.

Amsler Grid as seen with normal vision As seen with normal vision

Amsler grid as seen by person with eye disease An example of an abnormal Amsler Grid

What causes diabetic eye disease:

The leading cause of new cases of blindness and low vision in adults aged 20-65 is caused by diabetic retinopathy. “Retinopathy” is a general term that describes damage to the retina, which is the a structure in the back of the eye. The retina is a thin, light-sensitive tissue that lines the inside surface of the eye. Nerve cells in the retina convert incoming light into electrical impulses. These electrical impulses are carried by the optic nerve to the brain, which then interprets them as visual images. When diabetes becomes uncontrolled, the excess sugar causes damage to the small blood vessels. These blood vessels transport oxygen and other nutrients that nourish the tissue and nerve cells in the retina. Without proper blood flow, these areas of the retina become damaged or ischemic.

Symptoms of Diabetic Retinopathy Can Include

Blurry vision or double vision
Flashing lights, which can indicate a retinal detachment
A veil, cloud, or streaks of red in the field of vision, or dark or floating spots in one or both eyes, which can indicate bleeding
Blind or blank spots in the field of vision

Simulation of the effects of diabetic retinopathy

A simulation of the ocular and functional effects of diabetic retinopathy Henry Ford Center for Vision Rehabilitation and Research

Ocular and Functional Effects of Diabetic Retinopathy Can Include Any or All of the Following:

Fluctuating vision in response to changing blood glucose levels; vision can change from day to day, or from morning to evening.
Blurred central vision from macular edema can interfere with reading.
Decreased visual acuity can interfere with seeing the markings on an insulin syringe or the display on a standard blood glucose monitor.
Irregular patches of vision loss or “blind spots” can make it difficult to judge the size of food portions on a plate.
Decreased depth perception, in combination with decreased visual acuity, can make it difficult to see curbs and steps, or walk to the diabetes clinic.

How Diabetes Affects the Eyes and Vision: Diabetic Retinopathy

Although individuals with diabetes are more likely to develop cataracts at a younger age and are twice as likely to develop glaucoma as are non-diabetics, the primary vision problem caused by diabetes is diabetic retinopathy, the leading cause of new cases of blindness and low vision in adults aged 20-65:

“Retinopathy” is a general term that describes damage to the retina.
The retina is a thin, light-sensitive tissue that lines the inside surface of the eye. Nerve cells in the retina convert incoming light into electrical impulses. These electrical impulses are carried by the optic nerve to the brain, which interprets them as visual images.
Diabetic retinopathy occurs when there is damage to the small blood vessels that nourish tissue and nerve cells in the retina.
“Proliferative” is a general term that means to grow or increase at a rapid rate by producing new tissue or cells. When the term “proliferative” is used in relation to diabetic retinopathy, it describes the growth, or proliferation, of abnormal new blood vessels in the retina. “Non-proliferative” indicates that this process is not yet occurring.

Vivian: Living with Diabetes and Visual Impairment

Vivian is a quiet-spoken woman who has strong opinions and religious beliefs and a dignified determination. She describes herself as being extremely stubborn! Vivian was diagnosed with diabetes 20 years ago. Ten years later, she was diagnosed with diabetic retinopathy and spinal stenosis. Says Vivian, “Since I’ve had these problems, I’ve learned to appreciate what I have. I can wake up in the morning and still see the clouds, the sky, trees, flowers, and birds, even though they’re not clear. I realize I’m not blind and I’m very grateful for that. Also, I’ve discovered that people want to help. Since I’ve had problems with my sight, I find that so many people are very considerate. They open doors for me, and they help out if they see me struggling. I’ve realized that people really do have good hearts. In my own circle of friends, I don’t know anyone with vision loss, but they’ve totally accepted my situation. Learn more about the many ways you can self-manage your diabetes and lead an independent life:

Blood glucose monitoring
Insulin and insulin measurement
healthy eating and food preparation
Check out our Getting Started Kit for more ideas to help you live well with low vision.

What Are the Different Types of Diabetic Retinopathy?

There are two major types of diabetic retinopathy: non-proliferative diabetic retinopathy and proliferative diabetic retinopathy.

Non-proliferative diabetic retinopathy is the less severe form. In the mild non-proliferative retinopathy stage, small areas of balloon-like swelling occur in the retina’s small blood vessels. This is able to be seen by your doctor as small spots of blood. Moderate non-proliferative retinopathy causes more blood vessels to be damaged – causing worsening damage to the retina. Severe non-proliferative retinopathy is classified as many more blood vessel damage that disrupts the blood supply of the retina. This damaged retina causes a release of a signal to produce new blood vessels.
“Proliferative” is a general term that means to grow or increase at a rapid rate by producing new tissue or cells. When the term “proliferative” is used in relation to diabetic retinopathy, it describes the growth, or proliferation, of abnormal new blood vessels in the retina. This happens because the damaged retina attempts to protect itself by creating new blood vessels through a messenger protein called VEGF. However, this attempt is futile as those new blood vessels are abnormal being weak, rupture and bleed. Those new blood vessels grow throughout the retina as well as the vitreous, the transparent gel that fills the interior of the eye. These blood vessels then cause hemorrhages, scar tissues which can develop and tug on the retina causing further damage or even retinal detachment.

In addition, fluid can leak into the macula, the small sensitive area in the center of the retina that provides detailed vision. This fluid can cause macular edema (or swelling), which can occur at any stage of diabetic retinopathy, although it is more likely to occur as the disease progresses.

What will happen at my appointment?

As you may not notice any signs of diabetic retinopathy, the best way to protect your sign from diabetic retinopathy is to have regularly scheduled annual eye examinations. During this examination, an ophthalmologist or optometrist will be able to assess how healthy your retina is and if you have any signs of diabetic retinopathy by doing a comprehensive medical eye examination, which includes all of the following components:

A Health and Medication History

Your overall heath and how many years you have had diabetes
The medications you are taking for diabetes (insulin or oral medications)
Your most recent A1C
Questions about any other vascular diseases such as high blood pressure, history of stroke, coronary artery disease

Visual Acuity Testing

Distance and near vision acuity tests to determine the sharpness or clarity of your reading and distance vision
Testing your vision with different lenses (sometimes contained in a machine called a phoropter) to determine if your vision can be improved or corrected with regular glasses or contact lenses

An Eye Health Evaluation

A pen light is used to assess for an relative afferent pupillary defect, which can indirectly help your doctor determine if there is a nerve dysfunction in one eye as compared to the other eye
A tonometer, machine used to check pressure, is used to assess the amount of aqueous humor or pressure within your eyes. There are various ways and instruments to measure the pressure inside your eyes including a machine that ejects a puff of air, a pen-like probe that taps the surface of your eye, or a tool on the slitlamp itself that taps the surface of your eye. Your doctor might also refer to this pressure as intraocular (“within the eye”) pressure, or IOP.
A special microscope, called a slit lamp, is used to examine the anterior segment of the eye (front third of the eyeball), including the cornea, pupil, iris, lens, and aqueous drainage structures. Specifically, your doctor will look to see if there are any signs of blood vessels growing on your iris which is a sign of proliferative diabetic retinopathy due to the abnormal blood vessel growth
A dilated eye (or fundus) examination that can be achieved with the use of special lenses will allow your doctor to see inside your eye and examine the retina. Your doctor might choose to use eye drops to see the retina and optic nerve more clearly. During this exam, the doctor will examine your macula, or the center part of your vision, to see if there are any signs of fluid or swelling. You will then be asked to look in different directions so that your doctor can examine every section of your retina to assess for signs of bleeding, swelling, abnormal blood vessels and more.

Additional Tests for Diabetic Retinopathy

If your eye doctor suspects that your diabetic retinopathy is progressing, you will need to undergo additional testing that can help your doctor make a more definitive diagnosis of the stage of retinopathy

Gonioscopy

Examining the drainage system of the eye is an important aspect of the assessment for Proliferative Diabetic Retinopathy. The abnormal blood vessels can grow from the retina, through the vitreous (the transparent gel that fills the interior of the eye), and reach the front part of your eye by invading the iris and the drainage system of the eye. If this were to occur, the diagnosis can then shift from “Proliferative Diabetic Retinopathy” to “Neovascular Glaucoma” a severe complication of proliferative diabetic retinopathy. Neovascular Glaucoma is a secondary form of Open Angle Glaucoma (link to open angle glaucoma) that is caused by the blocked of the drainage system by abnormal blood vessels created by a damaged retina. In these cases, the eye’s ability to drain fluid, or aqueous humor, is blocked by these abnormal blood vessels causing an increased eye pressure which then can cause damage to the optic nerve.
In order to view the drainage system of the eye, a mirrored contact lens test called a gonioscopy must be done. To do this exam, the doctor will numb the surface of your eye with an anesthetic drop. Then a lens, called a gonioscope, is placed on the surface of your eye like a large contact lens. The doctor will have you look straight ahead, then use the slit lamp to look through the lens and see if there are any blood vessels in the drainage system

OCT

As diabetic retinopathy progresses, fluid can leak into the macula, the small sensitive area in the center of the retina that provides detailed vision.
This is able to be assessed by your doctor subjectively by looking at macula. However, your doctor may want to assess this objectively with a machine that measures the swelling of the macula. This test is done through a non-invasive imaging test called an Optical Coherence Tomography, or OCT.
The technician or ocular photographer will have you rest your head on a chinrest and look straight at a target. The machine will then focus on your macula and scan the area in order to measure the thickness of each direction. Your doctor will be able to view these results and assess progression of macular edema by comparing this results with any past or future test results.

Fluorescein Angiography

In order to assess the degree of diabetic retinopathy better, a special kind of picture called “Fluorescein Angiography” can be done in office. It takes less than 30 minutes
Your eyes will be dilated pr
The technician or ocular photographer will have you rest your head on a chinrest and look straight at a target. The machine will then focus on your retina in preparation to take photos.
A yellow colored dye, called fluorescein, is then injected into a vein in your arm. This dye allows blood vessels to shine brightly. It takes about 15 seconds for this dye to travel throughout your body. Eventually the fluorescein will reach the blood vessels in the back of your eye, or your retina. At this time, the special camera will takes photos of your retina. Your doctor will then be able to view these results and assess the level of leakage, swelling, blood, new abnormal blood vessels and more are in the back of your eye.