A bloodshot eye is redness on the white part of the eye, known as the sclera. This redness, medically termed conjunctival injection, occurs when the tiny blood vessels on the eye’s surface swell or rupture. While the sudden appearance of a red eye can be alarming, it is often a minor, temporary condition that resolves without intervention. Understanding the cause and the mechanics behind the redness helps determine when to seek professional care.
How the Eye Becomes Red
The eye’s redness is caused by changes in the conjunctiva, the thin membrane covering the sclera. One common way the eye turns red is through generalized redness, which involves vascular dilation. In response to irritation or inflammation, the numerous small blood vessels within the conjunctiva swell and widen, allowing more blood flow, which makes the eye appear diffusely pink or red. This pattern of redness is often associated with conditions that cause widespread surface irritation.
A second, more localized mechanism is a subconjunctival hemorrhage. This occurs when a fragile, small blood vessel beneath the conjunctiva breaks. Since the blood is trapped between the conjunctiva and the sclera, it cannot disperse, creating a sharply demarcated red patch. This type of redness, while visually striking, is usually painless and does not affect vision because the bleeding is superficial.
Common Causes of Eye Redness
Redness from generalized vascular dilation is frequently triggered by environmental and lifestyle factors. Eye strain from prolonged screen use, lack of adequate sleep, and exposure to airborne irritants like smoke or dry air can cause irritation. Seasonal allergies, where the eyes react to pollen or pet dander, also lead to redness accompanied by itching and tearing. The overuse or improper cleaning of contact lenses can also deprive the cornea of oxygen, irritating the eye and causing vessel dilation.
The localized redness of a subconjunctival hemorrhage is typically caused by physical actions that temporarily spike venous pressure. This can include violent coughing, forceful sneezing, vomiting, or straining during heavy lifting. Certain systemic factors can also increase the susceptibility of these vessels to rupture, notably the use of anticoagulant medications or aspirin. Underlying chronic conditions such as high blood pressure or diabetes can also contribute to vessel fragility.
Infections and inflammation are also frequent causes of diffuse redness. Conjunctivitis, commonly called pink eye, is an inflammation of the conjunctiva that can be caused by viruses or bacteria, leading to widespread redness often with discharge. Other inflammatory conditions like blepharitis, which involves the edges of the eyelids, can also cause persistent irritation. More serious internal inflammations, such as iritis or uveitis, affect deeper structures and present with a more intense pattern of redness.
When to Consult a Healthcare Professional
While many cases of eye redness are minor, the presence of certain accompanying symptoms warrants prompt professional evaluation. Seek immediate assessment if you experience:
- Any sudden change in vision, such as blurriness or double vision.
- Severe, deep eye pain or an extreme sensitivity to light (photophobia).
- Thick, colored discharge, particularly yellow or green pus, suggesting an active infection that may require prescription treatment.
A medical consultation is also necessary if the redness is the result of direct trauma or a chemical exposure. Redness that persists for longer than 7 to 10 days without showing any improvement should be evaluated. Furthermore, if eye redness is accompanied by systemic symptoms like a severe headache, nausea, or fever, it may indicate a serious condition requiring urgent care.
Self-Care and Recovery Timeline
For minor redness due to simple irritation, self-care measures can provide symptomatic relief. Applying a cool compress over closed eyelids can help reduce surface inflammation and provide comfort. The use of over-the-counter lubricating eye drops, also known as artificial tears, can soothe the irritated surface and help flush out minor irritants. It is advisable to avoid rubbing the eyes and to temporarily switch from contact lenses to glasses to allow the eye to rest and recover.
The recovery timeline depends on the cause of the redness. Simple irritation or eye strain may resolve within a few hours or a day after the irritant is removed. A subconjunctival hemorrhage, however, takes longer to clear because the trapped blood must be reabsorbed by the body. This process typically takes between 7 and 14 days, though larger hemorrhages may persist for up to three weeks. As the hemorrhage resolves, the bright red spot may change color, fading to yellow or orange, which is a sign of healing.