What Causes Red Blood Vessels in the Eyes?

Red blood vessels visible in the eyes—commonly referred to as “bloodshot eyes”—refer to the dilation of capillaries in the bulbar conjunctiva and superficial sclera, or subconjunctival hemorrhage, observable under natural light or focused lighting. Based on the location of capillary congestion, bulbar conjunctival hyperemia can be classified into conjunctival hyperemia, ciliary hyperemia, mixed hyperemia, and localized hyperemia. So, what causes red blood vessels in the eyes? The following explains this issue.

Causes of Red Blood Vessels in the Eyes

1. Inflammation

Ocular hyperemia with visible red blood vessels may indicate conjunctivitis. In addition to redness, conjunctivitis commonly presents with photophobia and dry eyes. It is typically caused by poor ocular hygiene—for example, rubbing the eyes with unwashed hands or wiping them with contaminated towels, tissues, or wet wipes. If red blood vessels result from conjunctivitis, patients should avoid rubbing their eyes and may be treated with topical antibiotic eye drops.

2. Elevated Intraocular Pressure

Increased intraocular or orbital pressure can impair local circulation, leading to venous stasis and congestion. This is frequently observed in acute angle-closure glaucoma and orbital space-occupying lesions. Additionally, systemic “heatiness” (a traditional Chinese medicine concept associated with inflammation and excess internal heat) may also cause ocular hyperemia and subsequent red blood vessels. Treatment with heat-clearing and fire-draining medications may help resolve the redness.

3. Sleep Deprivation

Red blood vessels upon waking are common and, if not accompanied by pain, foreign-body sensation, or excessive tearing, generally do not warrant concern. Ensuring adequate sleep—ideally 8–10 hours per night—and avoiding late-night activities usually restores normal appearance. For more severe cases, patients should consult a physician for appropriate topical ophthalmic therapy.

The above outlines common causes of red blood vessels in the eyes. Additionally, abnormal venous return may also contribute to this condition. If prominent, tortuous blood vessels are observed, impaired venous drainage from the eye may be present—potentially indicating serious conditions such as cavernous sinus thrombosis or cavernous sinus arteriovenous fistula. In such cases, prompt medical evaluation and treatment are essential. We hope this information is helpful to you.