How Diabetes Affects Your Vision: What You Need to Know  

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Diabetes mellitus (usually referred to as diabetes) is a chronic carbohydrate metabolism disorder resulting from inadequate production or utilization of the hormone insulin. When a person has diabetes, their pancreas either doesn’t make enough insulin or their body cannot use it effectively. Diabetes is an illness that makes it hard for your body to use the food you eat the right way.  

It is characterized by a high glucose level in the bloodstream, known as hyperglycemia. Glucose is the principal circulating sugar in the blood and is the first energy source for all cells in the body. Glucose is also called “sugar.”    

However, cells cannot use glucose without the help of insulin, a hormone produced by the pancreas that helps move glucose out of the bloodstream into cells, used for energy to fuel everyday activities.  

Types of Diabetes  

• Type 1 diabetes (formerly called juvenile-onset, Type I, or insulin-dependent).  

• Type 2 diabetes (formerly called adult-onset, Type II, or non-insulin dependent)  

• Gestational diabetes  (develops in the 24th- 26th week of pregnancy) and a few less common types  

You can find out more about diabetes through the American Diabetes Association. They offer an “Ask Dr. Bob Feature” with several videos on many aspects of diabetes.  

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 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. The optic nerve carries these electrical impulses to the brain, which 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.  

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. Your doctor can see this 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 retina’s blood supply. This damaged retina causes the release of a signal that produces new blood vessels.  

• “Proliferative” is a general term that means rapidly growing or increasing 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 VEGF messenger protein. However, this attempt is futile as those new blood vessels are abnormally weak, rupturing, and bleeding. Those new blood vessels grow throughout the retina and the vitreous, transparent gel that fills the eye’s interior. These blood vessels then cause hemorrhages and 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 retina’s center 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.  

Diabetic Retinopathy Symptoms 

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, can indicate bleeding  

• Blind or blank spots in the field of vision  

Functional Effects of Diabetic Retinopathy 

• 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 judging the size of food portions on a plate difficult.  

• Decreased depth perception and decreased visual acuity can make it difficult to see curbs and steps or walk to the diabetes clinic.  

Diagnosing Diabetic Eye Disease: Comprehensive Eye Examination Procedures 

You may not notice any signs of diabetic retinopathy. It is important to have regularly scheduled annual eye examinations when you have diabetes. 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:  

• Your overall health 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 

An ophthalmologist or optometrist will assess your visual acuity. Testing will include: 

• 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 penlight is used to assess for a 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, a machine used to check pressure, assesses 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 slit-lamp 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 use eye drops to see the retina and optic nerve more clearly. During this exam, the doctor will examine your macula, or the center of your vision, to see 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 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 eye’s drainage system 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 eye’s interior) 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 could 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 caused by the drainage system’s blockage 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. 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.  

• An ophthalmologist can use a machine that measures the swelling of the macula. The test is non-invasive imaging 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 to measure the thickness of each direction. Your doctor will be able to view these results and assess the progression of macular edema by comparing these results with any past or future test results.  

Fluorescein Angiography  

• To assess the degree of diabetic retinopathy better, a special kind of picture called “Fluorescein Angiography” can be done in the office. It takes less than 30 minutes. 

• Your eyes will be dilated. 

• 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 injected into your arm’s vein. 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 your retina. At this time, the special camera will take photos of your retina. Your doctor can then assess the level of leakage, swelling, blood, and new abnormal blood vessels in the back of your eye.  

By Debra A. Sokol-McKay,  
MS, CDE, OTR/L, SCLV,  

Updated by Sefy Paulose, M.D., March 2022