“Why do I have blurry vision?” Understanding what causes blurred vision

Medically reviewed by Rosanna Sutherby, PharmD on March 31, 2021. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

There is a wide range of reasons why your vision can change. Vision issues can be a natural part of aging for many people, but they can sometimes point to more serious health issues, including diabetes. Read on to learn more about blurry eyesight and its relationship with diabetes.

If you have diabetes or prediabetes, it’s important to monitor your HbA1c levels (HbA1c is an indicator of the average sugar level in your blood over the past 3 months). To check your HbA1c from the convenience of home, try the Everlywell HbA1c Test kit—which comes with everything you need to easily collect a small blood sample at home and send it to a lab for testing.

Why is my vision blurry?

Blurry vision simply refers to a loss of sharpness in your eyesight. Blurred vision can cause things to look hazy or out of focus, which can get worse in dim lighting. It can also make it difficult to read or make out the details of people or objects.

So what causes blurry vision? Refractive errors are the main cause of blurriness and primarily include myopia (nearsightedness), hyperopia (farsightedness), and astigmatism (due to a misshapen cornea or lens). Structures in the eyes have refractive properties that essentially bend and focus light into a specific point to create a sharp image. That focus point should ideally be the retina; however, light can be deflected, reflected, and bent by all sorts of materials and surfaces in the environment that focus the light elsewhere.

Refraction starts in the cornea, which is the curved, clear structure at the front of the eye. Light rays also get bent in the lens of the eye. Even the fluids in the eyes and the tear film on the eye’s surface contribute to refraction.

Refractive errors that cause blurriness mainly come from three factors:

• Eye length: If the eye is too long, light gets focused at a point before it reaches the retina, causing nearsightedness. A shorter eye creates a focus point beyond the retina, creating farsightedness.
• Lens curvature: The eye lens is naturally curved, but that curve should be appropriate in relation to the other structures of the eye. A lens that is too sharply curved creates nearsightedness, while a flatter lens contributes to farsightedness.
• Corneal curvature: The corneas are designed to be nearly perfectly spherical, but a shift in that spherical curvature can cause refractive errors.

Refractive errors can come from a wide variety of factors, from hormonal changes during pregnancy to certain medications. Presbyopia is an age-related cause of blurry vision. Proteins in the eye lens may change and make the lens harder and less elastic as you age. Muscle fibers around the lens may also create problems with the elasticity of the lens. All of this can make it hard for the eye to focus clearly on objects.

Diabetes and blurry vision

Diabetes mellitus (simply referred to as diabetes) is a condition that is characterized by the body’s inability to properly use blood sugar, or glucose. Glucose is your body’s main source of energy, and while it is necessary to keep your cell’s functioning, diabetes contributes to excess levels of glucose in the blood. This can lead to some severe health issues, including blurry eyesight.

Related: How many people have diabetes?

At first glance, it may seem strange that diabetes might affect the eyes—but glucose fuels the cells in the body, including those in and around the eyes. High blood sugar levels can potentially cause blurry vision because higher amounts of glucose pull more water into your eyes’ lenses, causing them to swell. That swelling can cause a change in vision. This can be one of the initial signs of diabetes or a sign that your diabetes is advancing out of control.

Thankfully, this kind of blurry vision is often temporary and frequently goes away as you manage your glucose levels, but be sure to discuss this symptom with your diabetes care team to ensure you know what precautions to take.

However, diabetes can also cause blurry vision in other ways that may not be reversible. High blood sugar levels over an extended period of time can cause thinning and weakening within the blood vessels of the retina. Over time, these weak areas can bulge and form small pouches of blood called microaneurysms. Retinal microaneurysms can eventually leak proteins called exudate. If exudate reaches the center of the retina (called the macula), it can contribute to swelling and thereby lead to vision changes. Left untreated, these vision changes can potentially become permanent.

Easily check your HbA1c—an indicator of the average sugar level in your blood over the past 3 months that’s routinely used for diabetes management—with the Everlywell at-home HbA1c Test.

Diabetes and other eye issues

Due to the nature of diabetes and how sensitive eyes are, high blood sugar levels can have a whole host of other effects on the eyes. This category of eye problems is known as diabetic eye disease, and beyond blurry vision, they can contribute to vision loss and other serious issues.

Retinopathy

Diabetic retinopathy is a continuation of the damage to retinal blood vessels. Blood can eventually leak out of the blood vessels and create hemorrhages. These hemorrhages get worse as the blood vessels in your eye get blocked, which prevents blood flow to the retina. This prevents sufficient oxygen or nutrients from reaching the retina.

To adapt, the retina will attempt to grow new blood vessels, but these are weak and can’t support the retina’s blood needs. The weak blood vessels can potentially leak blood into the eye and may ultimately lead to blindness.

Glaucoma

The optic nerve refers to a bundle of nerves that connects the eye to the brain, allowing for communication between the two. Glaucoma refers to damage to the optic nerve, which can lead to vision loss if left untreated.

Cataracts

Your eye lenses can get cloudy with age, developing into cataracts. While cataracts can affect anyone, people with diabetes are more likely to develop this eye problem. Research suggests that the high blood sugar levels may make it easier for deposits to form on your lenses.

Diabetic macular edema

As mentioned, the macula is the center of your retina. It’s what you use when you read, drive, or look at anything with any amount of detail. Diabetic macular edema refers to a swelling in the macula. As this eye problem progresses, one loses the ability to see things sharply, which can lead to a vision change or even vision loss. This eye condition is more common among those who also show signs of diabetic retinopathy.

Maintaining eye health

Among the best ways to maintain good eyesight is to keep your blood sugar under control and maintain regular eye exams with your eye doctor. Controlling your blood sugar can prevent new eye problems while slowing (or even reversing) the progression of existing issues. If you’ve been diagnosed with diabetes, be sure to have a conversation with your diabetes care team about what steps you can take to maintain your eye health.

More on diabetes: Why am I so thirsty all of a sudden?

Regular HbA1c testing is a cornerstone of many diabetes treatment plans and can help you track your progress towards achieving glycemic control. To check your HbA1c from the convenience of home, take the Everlywell at-home HbA1c Test (which requires only a simple finger prick for sample collection).

References

1. The Vision Council. Organizational overview. URL. Accessed March 31, 2021.

2. Refractive errors and refraction: How the eye sees. All About Vision. URL. Accessed March 31, 2021.

3. Diabetes. Mayo Clinic. URL. Accessed March 31, 2021.

4. Eye damage with diabetes. Kaiser Permanente. URL. Accessed March 31, 2021.

5. Diabetic Eye Disease. National Institute of Diabetes and Digestive and Kidney Diseases. URL. Accessed March 31, 2021.