Diabetes affects the body’s ability to produce or use insulin effectively to control blood glucose (sugar) levels. Excessive glucose in the blood causes damage to the small blood vessels of the body, including circulation of the eye. Optometrists can detect indicators of diabetes before the disease is formally diagnosed.  As such, comprehensive eye exams can lead to early diagnosis of diabetes and minimize the risk of other life-threatening complications such as heart disease and stroke.

Effects of Diabetes on the Eye

Diabetes-related eye problems that can be detected by your optometrist include:


Diabetic retinopathy results from the damage diabetes causes to the small blood vessels located in the retina. NPDR is the earlier stage of the disease. The blood vessels of the retinal are weakened, causing them to leak and the retina to swell. Symptoms at this stage vary from nonexistent to moderate changes in vision.


PDR is the more advanced form of the disease. In an attempt to improve blood supply to the retina, new, fragile blood vessels can begin to grow in the retina and into the vitreous, the gel-like fluid that fills the back of the eye. The new blood vessels may leak blood into the vitreous, clouding vision. Complications of PDR include glaucoma and retinal detachment. PDR can cause severe vision loss and even blindness.


Cataracts are an opacification of the lens inside the eye, causing cloudy vision and glare. Individuals with diabetes develop cataracts earlier in life and their cataracts tend to progress at a faster rate. In the body, glucose is reduced to the sugar-alcohol sorbitol. The accumulation of sorbitol in the lens of the eye leads to cataract development. The production of sorbitol in diabetic patients (as compared to nondiabetic patients) takes place more quickly than it can be converted into useful by products.1


In patients with proliferative diabetic retinopathy, new blood vessels can progress forward from the retina to the iris and anterior chamber angle of the eye. Here, they can occlude the drainage structure of the eye (the trabecular meshwork), causing the pressure in the eye to increase rapidly, and neovascular glaucoma to develop. Glaucoma leads to irreversible vision loss if not detected and treated at an early stage. Moderate evidence also suggests that diabetes is a risk factor for developing open-angle glaucoma.2


Damage to blood vessels from diabetes can result in interruption of blood supply to nerves. When blood flow to certain nerves in the head (called cranial nerves) is blocked, it can cause full or partial paralysis of muscles that move the eye. This causes to eye misalignment and subsequent double vision.3


Diabetes can damage the nerve endings of the cornea (the clear dome-shaped covering the front of the eye).  This can prolong healing time following injury and lessen the cornea’s ability to respond to stimulation, such as a foreign body.4

Other ocular complications associated with diabetes include:

•   frequent & transient prescription changes
•   retinal vascular occlusions
•   ocular ischemic syndrome
•  ischemic optic neuropathy

The less controlled one’s blood sugar is and the longer one has had diabetes for, the more likely they are to develop diabetes-related eye conditions. If blood sugar is too high for too long, the small blood vessels that keep the retina healthy will become permanently damaged. Annual eye exams are critical for people living with diabetes, and are covered by OHIP regardless of age.

Can you prevent diabetic eye disease?

To prevent retinopathy or prevent it from getting worse, Diabetes Canada advises following the ABCDEs of staying healthy with diabetes:5

A – A1C

Most people should aim for an A1C* of 7%** or less by managing blood sugars well.

B – Blood Pressure

Control your blood pressure to less than 130/80** mmHg.

C – Cholesterol

The LDL (bad) cholesterol target is less than 2.0** mmol/L.

D – Drugs to Protect Your Heart

Speak with your health-care team about medications.

E – Exercise & Eating

Regular physical activity, healthy eating, and maintaining a healthy body weight.

S – Screening For Complications

Ask your health-care team about tests for your heart, feet, kidneys, and eyes.

S – Smoking Cessation

Stop smoking and seek support for help with quitting.

S – Self-Management, Stress & Other Barriers

Set goals for yourself to reach targets and live well with diabetes, such as managing stress effectively.


* A1C is a blood test that is a measure of your average blood sugar level over the past 120 days.

**Discuss your target values with your health-care team. Note that A1C targets for pregnant women, older adults and children 12 years of age and under are different