Blurriness that affects only one eye, known as unilateral blurry vision, is a common symptom prompting people to seek an eye examination. This change indicates something is interfering with how light focuses on the retina or how the visual signal travels to the brain. Causes range from minor, easily correctable issues to serious, sight-threatening conditions. Understanding the potential problems within the eye’s structures is the first step in determining the urgency of the symptom.
Common Refractive and Surface Causes
The most frequent reasons for unilateral blurriness relate to the eye’s shape or the quality of its tear film. Refractive errors, such as nearsightedness (myopia), farsightedness (hyperopia), or astigmatism, can cause vision to gradually blur in one eye more than the other. This happens when the length of the eyeball or the curvature of the cornea or lens changes, preventing light from focusing precisely onto the retina.
Astigmatism involves an irregularly shaped cornea or lens that causes light to scatter unevenly, resulting in distorted vision. A shift in the degree of a refractive error in just one eye might make the blurriness noticeable. These conditions are managed with updated prescription glasses or contact lenses.
Another common cause is mild dry eye syndrome, especially when one eye is affected more severely. The tear film provides a smooth surface for light to pass through; when compromised, the surface becomes irregular, leading to temporary or fluctuating blurriness. Eye strain or fatigue from prolonged visual tasks, like staring at a computer screen, can also temporarily reduce visual acuity in one eye.
Acute Issues of the Eye’s Front Structures
A sudden onset of blurriness often points to an acute problem with the eye’s front structures, specifically the cornea or the lens. The cornea, the clear outer layer, is susceptible to physical damage, such as a corneal abrasion (a scratch). This injury, often caused by a foreign object, contact lens misuse, or trauma, can introduce significant pain and cloud the vision by disrupting the smooth corneal surface.
Infections of the cornea (keratitis) or severe bacterial or viral conjunctivitis can also cause rapid unilateral blurriness. These conditions involve inflammation and swelling that change the cornea’s transparency, hindering light transmission. If left untreated, severe infections can progress to a corneal ulcer, which poses a serious threat to vision.
The natural lens can also be a source of acute blurriness if a cataract develops more rapidly or prominently in one eye. A cataract involves the clouding and hardening of the lens, which blocks and scatters light before it reaches the retina. While usually age-related and slow to progress, the resulting blurriness, often accompanied by glare or halos around lights, may be first noticed in the eye where the clouding is most advanced.
Serious Conditions Affecting the Posterior Eye
Blurriness originating from the posterior section of the eye (the retina and optic nerve) is often associated with severe and time-sensitive conditions. One urgent cause is a retinal detachment, where the light-sensitive retina pulls away from its underlying supportive tissue. This separation deprives the retinal cells of oxygen and nutrients, leading to a loss of clear vision, which may be preceded by a sudden increase in floaters or flashes of light.
Vascular events, commonly referred to as an “eye stroke,” involve blockages in the blood vessels supplying the retina or optic nerve. A retinal artery occlusion occurs when the central retinal artery is blocked, causing sudden and often profound, painless vision loss in one eye. Similarly, the optic nerve, which transmits visual information to the brain, can become inflamed in a condition called optic neuritis.
Optic neuritis, often linked to autoimmune conditions like multiple sclerosis, causes blurriness or complete vision loss, sometimes accompanied by eye pain, due to the disruption of nerve signaling. Another serious condition is the “wet” form of age-related macular degeneration (AMD). This involves the rapid growth of abnormal, leaky blood vessels beneath the macula, causing leakage of fluid or blood that quickly distorts or blurs the central vision in one eye.
When Blurry Vision Requires Immediate Attention
A sudden change in visual clarity, especially in only one eye, warrants immediate medical assessment to rule out a sight-threatening emergency. Seek urgent care if the blurriness appears abruptly and significantly affects your vision, even if it resolves quickly. Any blurriness accompanied by flashes of light, a shower of new floaters, or the sensation of a curtain or shadow moving across the vision field should be treated as an immediate emergency, as these are signs of a potential retinal detachment.
Immediate attention is also necessary if the blurriness is paired with severe eye pain, intense headache, nausea, or vomiting, which can indicate acute angle-closure glaucoma. If the visual change occurs alongside neurological symptoms, such as sudden weakness or numbness on one side of the body, difficulty speaking, or a loss of balance, it could signal a stroke or transient ischemic attack (TIA). In such cases, contacting emergency services or going directly to the emergency room is appropriate.