Bloodshot eyes, also known as conjunctival hyperemia, occur when the tiny blood vessels on the surface of the sclera (the white part of the eye) dilate. This causes one or both eyes to appear pink or red. The redness can develop gradually or appear suddenly.

Conjunctivitis, commonly known as pink eye, is a frequent cause of red eyes. This condition results from bacterial or viral infections, or allergies. It makes one or both eyes bloodshot, swollen, watery, and itchy. While rarely serious, pink eye is highly contagious and can lead to significant discharge, requiring individuals to take a few days off from school or work.

Blepharitis is an inflammation of the eyelid margins, often causing red eyes. Symptoms include a burning sensation, crusting, itching, and swelling. Common causes are bacterial overgrowth, Demodex mites (eyelash mites), and reduced oil secretion from the meibomian glands.

A subconjunctival hemorrhage occurs when a small blood vessel beneath the conjunctiva breaks. This causes blood to pool, forming a bright red patch on the white of the eye. This condition is typically painless and usually resolves on its own.

A stye is a small, red, swollen lump on the eyelid, caused by a bacterial infection in a blocked sebaceous gland. It often resembles a pimple. Early signs include localized redness, swelling, and pain. Most people experience a stye at least once in their lifetime.

Glaucoma refers to a group of diseases that damage the optic nerve due to elevated intraocular pressure. The optic nerve (cranial nerve II) is a bundle of nerve fibers connecting the retina to the brain, transmitting electrical signals from retinal ganglion cells to the occipital lobe for image processing.

Beyond red eyes, glaucoma symptoms can include blurred vision, deep eye pain, nausea, vomiting, seeing halos around lights, and eye swelling.

Corneal damage can also lead to red eyes. The cornea is the transparent layer at the front of the eyeball that helps focus light. Scratches on the cornea can result from aggressive eye rubbing, fingernails, foreign bodies, or dry eyes. Corneal tears, often caused by sharp objects, are an ophthalmologic emergency.

Improper use and cleaning of contact lenses can cause red eyes. Contact lenses can restrict oxygen flow to the cornea, leading to irritation and conjunctival hyperemia.

Alcohol consumption can also make your eyes red. After drinking, capillaries dilate, increasing blood flow to the conjunctiva. The more alcohol consumed, the more pronounced this dilation, leading to redder whites of the eyes.

Treatment for red eyes depends on the underlying cause. For mild cases, common measures include antihistamines (for allergies), cold compresses, over-the-counter eye drops, proper contact lens hygiene, and adequate rest. More severe conditions, such as infections, corneal damage, or glaucoma, may require prescription eye drops, oral medication, or surgical intervention as directed by an ophthalmologist.

Bao Bao (According to Health)