Blurry vision is a common symptom when the body is fighting an infection or acute illness. The answer to whether being sick can cause this temporary visual disturbance is yes, as systemic illness disrupts the body’s internal balance. This temporary blurriness is often a secondary effect of the body’s response to infection, rather than a direct problem with the eye itself. Understanding these physiological changes helps distinguish between a temporary symptom and a warning sign of a more serious issue.
Common Temporary Causes Linked to Systemic Illness
One of the most frequent systemic causes of temporary vision changes during illness is dehydration. When the body loses fluid due to fever, vomiting, or diarrhea, tear production decreases, leading to dry eyes. Tears are responsible for maintaining a smooth, clear surface on the cornea, and a compromised tear film results in fluctuating or blurry vision.
Severe fatigue and high fever also play a role in visual blurriness. Illness-related fatigue can affect the tiny muscles responsible for focusing the eye, making it difficult to maintain clear vision for tasks like reading or looking at a screen. High body temperature from a fever contributes to this general fatigue and places additional strain on the visual system.
Specific Physiological Disruptions Affecting Vision
Acute respiratory infections often involve significant swelling in the sinuses. When sinuses become inflamed and congested, the resulting pressure can push against the eye socket’s structures. This localized pressure can temporarily affect the nerves and muscles that control eye movement and focusing, leading to blurred vision or difficulty keeping images clear.
Temporary fluctuations in blood glucose levels are another specific disruption that can cause visual blurring, even in individuals who are not diabetic. During an acute infection, the body releases stress hormones that can cause blood sugar to rise, a condition known as hyperglycemia. High blood sugar causes fluid to shift into the lens of the eye, which makes the lens swell and temporarily alters its shape, resulting in blurry vision until glucose levels stabilize.
Direct inflammation of the eye’s surface can occur during a viral illness. Viral infections like the common cold or flu can sometimes spread to the eye, causing conditions such as keratitis (inflammation of the cornea) or conjunctivitis. Inflammation or swelling on the cornea interferes with light refraction and leads to blurred vision, pain, and redness.
How Medication Side Effects Contribute
In some cases, the medication taken to treat the illness is the actual source of the visual disturbance. Over-the-counter decongestants, which often contain ingredients like pseudoephedrine or phenylephrine, are known to stimulate the nervous system. This stimulation can sometimes cause the pupil to dilate, which can induce temporary blurriness and light sensitivity.
Antihistamines, commonly used for allergy or cold symptoms, can contribute to dryness throughout the body, including the eyes. By reducing tear production, these medications can exacerbate dry eye symptoms, leading to fluctuating or blurred vision. Additionally, both decongestants and antihistamines carry a small risk of precipitating an acute angle-closure glaucoma attack, which is a painful eye emergency accompanied by sudden, severe blurriness.
Urgent Symptoms Requiring Medical Attention
While mild, temporary blurriness during illness is common, certain accompanying symptoms signal a medical emergency requiring immediate attention. Sudden, severe, or complete loss of vision in one or both eyes warrants urgent care. Blurriness accompanied by intense eye pain, significant redness, or sensitivity to light (photophobia) may indicate serious internal inflammation, such as uveitis, or a sudden rise in eye pressure like acute angle-closure glaucoma.
The presence of double vision, new flashes of light, or a sudden increase in floating spots or a “curtain” blocking part of the visual field suggests a potential retinal issue, such as a detachment. Visual changes paired with neurological symptoms are especially concerning and warrant urgent evaluation. These symptoms include severe headache, difficulty speaking, facial weakness, confusion, or numbness on one side of the body, as they could indicate a stroke or a severe systemic infection affecting the central nervous system.