What Causes Blurred Vision?

Blurring vision can be described as difficulty seeing objects around you clearly, struggling to read text, or feeling like there’s a faint film over your vision. This can sometimes arise from temporary causes such as prolonged screen viewing or eye fatigue. In other instances, it may be a sign of an underlying issue that requires evaluation related to the eyes or overall health.

There is not a single cause for blurred vision. Changes in spectacle prescription, dry eyes, fluctuations in blood sugar, and cataracts can all affect visual acuity. Therefore, it is important to determine when the blurred vision began, whether it is seen in one eye or both eyes, and whether any other symptoms are present.

This article explains possible causes of blurred vision, which symptoms matter and when to consult an eye doctor in straightforward language.

Blurred vision is difficulty distinguishing details and edges clearly. A person may struggle to read distant signs, see nearby writing or recognise faces clearly.

People may describe blurred vision in these ways:

• It feels as though I am looking through a foggy window.

• The edges of letters run together.

• The image will not come into focus.

• It improves briefly when I blink.

• I see light scattering around lights.

• The image sometimes shifts or shakes.

The blurriness can be constant, or it can appear at specific times of the day. Specifically, blurriness that develops after a prolonged period of using a phone, tablet, or computer can be related to eye fatigue or dry eyes.

However, the evaluation of recurrent, progressively increasing, or sudden onset blurred vision should be performed through eye examinations.

For a clear image, light must pass through the front of the eye and focus correctly on the retina. The cornea, natural lens, tear film, retina and optic nerve contribute at different stages of this process.

A change in any of these structures can reduce image clarity. For example, an irregular tear film may cause blurring related to dry eye. Loss of transparency in the natural lens can reduce visual quality through cataract.

Common causes of blurred vision include:

• Refractive errors such as myopia, hyperopia and astigmatism

• Changes in spectacle or contact lens prescription

• Dry eye

• Eye strain from prolonged screen use

• Cataract

• Changes in blood glucose

• Migraine

• Blood pressure fluctuations

• Eye injuries

• Problems involving the retina or eye blood vessels

Blurred vision is not, in itself, a disease. It can appear as a symptom of various underlying conditions.

Blurred vision does not always mean a permanent eye condition. In some people it is brief and improves when the cause is removed.

Situations that may cause temporary blurred vision include:

Blinking may become less frequent while using a computer, phone or tablet. This can dry the ocular surface and temporarily blur vision.

Insufficient sleep can affect the eyes’ focusing performance. This can lead to a feeling of decreased visual clarity, especially in the later hours of the day.

Wearing contact lenses for a longer period than recommended can lead to dryness, irritation, and blurred vision of the eye surface.

Insufficient fluid intake in the body can affect tear production and the balance of moisture on the eye surface. As a result, temporary fluctuations in vision may occur.

Rapid rises or falls in blood sugar can temporarily affect the structure of the lens. Vision may therefore become blurred for a time.

If the blurred vision, which is thought to be temporary, frequently recurs or begins to affect daily life, it is recommended to undergo an examination to determine the underlying cause.

Blurriness that suddenly begins in a few minutes or within a few hours should be evaluated differently from slow-progressing vision problems.

Sudden blurred vision can develop due to reasons such as migraine, changes in blood sugar, or eye fatigue. However, an increase in intraocular pressure, or problems related to the retina or eye blood vessels, can also produce a similar symptom.

Seek medical care without delay if any of the following occurs:

• Sudden onset of vision loss

• Blurring developing in only one eye

• Loss of part of the visual field

• Flashes of light or numerous floaters

• Severe eye pain and redness

• Accompanying nausea and vomiting

• Speech difficulty or weakness on one side of the body

• An impact to the eye

• A marked reduction in vision over a short time

Do not wait for sudden vision loss or a marked change in vision to improve on its own. If it occurs with speech difficulty or weakness on one side, call 112.

The appearance of blurriness only in one eye, is often associated with a condition affecting that particular eye.

Possible causes of blurred vision in one eye include:

• Different prescriptions in the two eyes

• More pronounced dry eye in one eye

• An incorrectly positioned contact lens

• A scratch or damage to the corneal surface

• More advanced cataract in one eye

• Changes involving the retina or eye blood vessels

• A foreign body in the eye

• Eye injury

Cataracts may develop in both eyes but do not necessarily progress at the same rate. One eye may therefore see more blurred than the other.

Sudden and persistent blur in one eye must be evaluated by an ophthalmologist.

Blurred vision in both eyes may result from changes in the glasses prescription, dry eye or fatigue associated with screen use.

Fluctuations in blood sugar and blood pressure, as well as other general health problems, can lead to sudden and temporary vision changes in both eyes. Before or during a migraine attack, shimmering, flashing, or blurred vision may be experienced in both eyes.

If there is blurring in both eyes that has been ongoing for a long time, it is necessary to check the spectacle prescription and to perform a detailed eye examination.

Tears not only moisten the eyes, but also create a smooth optical layer on the front surface of the eye, which helps with clear vision.

If the tear film is insufficient or evaporates quickly, the clarity of the vision may be impaired. Blurriness associated with dry eye is often temporarily resolved after blinking, and then may recur.

Blurred vision in dry eye may be accompanied by:

• Burning and stinging

• A gritty sensation

• Redness

• Light sensitivity

• A feeling of heaviness in the eyes

• Watering

• Increased discomfort during screen use

The treatment for dry eye is planned according to the reason and severity of the complaint. Using random eye drops without a doctor’s recommendation may not be appropriate.

Myopia, hyperopia, and astigmatism, among the most common causes of blurred vision, can occur when the prescription for eyeglasses or contact lenses is not suitable for an individual’s needs, resulting in an inability to see distant or near objects clearly.

Signs that may suggest a prescription change include:

• Difficulty reading distant text

• Eyes tiring quickly during near work

• Headache

• Needing to narrow the eyes to see

• Difficulty focusing during screen use

• Unclear vision with current glasses

An eye examination is needed to determine the correct prescription. Measuring glasses alone may be insufficient, particularly when uncontrolled blood sugar causes temporary prescription changes.