High blood sugar can cause blurred vision.

Prolonged high blood sugar levels in people with diabetes can easily lead to damage to nerves and blood vessels in the eyes, causing reduced vision and potentially blindness.

According to Dr. Pham Huy Vu Tung, a specialist in Ophthalmology at Tam Anh General Hospital in Ho Chi Minh City, people with poorly controlled blood sugar levels are prone to eye complications. This can occur in both pre-diabetic and pre-diabetic patients. Some common eye complications include diabetic retinopathy, diabetic macular edema, cataracts, and glaucoma.

High blood sugar alters fluid levels, causing swelling of the tissues in the eye. These conditions are only temporary and resolve on their own when blood sugar levels return to normal.

If blood sugar is high for a long period, the small blood vessels at the back of the eye are prone to damage. New blood vessels develop, but they are weaker and tend to drain into the center of the eye, leading to scarring or dangerously high pressure. Most diabetic eye diseases originate from these blood vessels.

According to Dr. Tung, damage can begin during the pre-diabetic period (a condition where blood sugar is higher than normal but not high enough for a doctor to diagnose type 2 diabetes). People with diabetes who also have risk factors such as high cholesterol, smoking, and high blood pressure are more prone to eye diseases.

Doctor Tung examines a patient's eyes. Photo: Dinh Tien — Doctor Tung examines a patient's eyes. Photo: *Dinh Tien*

Here are four common eye diseases caused by diabetes.

Diabetic retinopathy : The retina is the innermost layer of the eyeball. It senses light and sends signals to the brain for decoding, allowing us to see. Damaged blood vessels affecting the retina cause diabetic retinopathy. Diabetic retinopathy is a common cause of vision loss.

Macular edema : The macula is a part of the retina located at the back of the eye, responsible for color perception and image detail. Diabetes can cause swelling of the macula (macular edema). Over time, macular edema can lead to partial vision loss or blindness.

Glaucoma : This occurs when the intraocular pressure in the eye increases, damaging the optic nerve, the nerve that connects the eye to the brain. Diabetes doubles the risk of developing glaucoma, leading to vision loss or blindness.

Cataracts: The lens is a transparent structure that helps the eye see objects more clearly. The lens tends to become cloudy with age. High blood sugar causes deposits to build up in the lens, increasing the risk of developing cataracts.

When experiencing vision problems due to high blood sugar, patients may have symptoms including blurred vision, wavy vision, darkened vision, poor color perception, hazy vision, flashing lights, and vision loss.

Dr. Tung added that good blood sugar control is the best way to prevent diabetic eye disease. Target blood sugar levels vary from person to person, but generally, the HbA1c (average blood sugar over three months) should be below 7%.

Dr. Tung advises patients to adhere to the treatment prescribed by their endocrinologist/diabetologist, monitor blood sugar levels, and have regular check-ups. Annual eye exams are recommended for five years after diagnosis of type 1 diabetes. Type 2 diabetes patients should have an eye exam immediately after diagnosis and at least once a year. Women with diabetes should have an eye exam before pregnancy or during the first trimester, and continue regular check-ups until one year after childbirth.

Dinh Tien

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