“Red eye” and “pink eye” are often used interchangeably, creating confusion about the seriousness of an eye condition. The distinction is straightforward: “red eye” is a general description of a symptom, while “pink eye” is the common name for the specific medical diagnosis, conjunctivitis. Redness indicates an underlying issue, but the cause can range from a minor irritant to a sight-threatening disease.
Red Eye as a General Symptom
The appearance of a red or bloodshot eye is a non-specific sign resulting from the dilation of blood vessels on the eye’s surface. This process, known as hyperemia, causes the small vessels in the conjunctiva and episclera to become engorged with blood and more visible. The conjunctiva is the thin, clear membrane covering the white part of the eye (sclera) and lining the inner surface of the eyelids.
Redness is the body’s reaction to inflammation, irritation, or infection. Inflammation triggers the release of substances like histamine, which cause blood vessel walls to widen. This widening increases blood flow, delivering immune cells and fluid that result in the characteristic red appearance. While the pattern of redness can offer clues, the symptom alone cannot provide a definitive diagnosis.
Pink Eye Specifics Conjunctivitis
Pink eye, or conjunctivitis, is an inflammation of the conjunctiva. This condition is the most common cause of eye redness and is categorized into three main types based on the underlying trigger. The infectious forms (viral and bacterial) are highly contagious and spread through contact with discharge or contaminated surfaces.
Viral conjunctivitis is the most frequent type, often accompanying a common cold or respiratory infection. It produces a clear, watery discharge and frequently begins in one eye before spreading to the other. Since it is caused by a virus, antibiotics are ineffective, and the condition typically clears up within one to two weeks.
Bacterial conjunctivitis is less common in adults and is identifiable by a thick, sticky discharge that is often yellow or green. This discharge can cause the eyelids to stick together, particularly upon waking. This form is generally treated with antibiotic eye drops or ointment to speed recovery.
Allergic conjunctivitis is not contagious and occurs when the eyes react to environmental triggers like pollen, dust, or pet dander. The defining symptom is intense itching in both eyes, often accompanied by tearing and other allergy symptoms. Treatment involves avoiding the allergen and using antihistamine eye drops or oral medications to manage the inflammatory response.
Other Serious Causes of Redness
Red eye can also signal conditions far more serious than conjunctivitis, requiring immediate medical attention to prevent vision loss. Acute angle-closure glaucoma is an emergency where fluid drainage is suddenly blocked, causing a rapid and painful spike in intraocular pressure. This condition often presents with severe, throbbing pain, sudden blurred vision, and the perception of colored halos around lights.
Uveitis involves inflammation of the uvea, the middle layer of the eye. Redness from uveitis is often concentrated in a ring around the iris, known as ciliary flush, and is accompanied by significant light sensitivity (photophobia) and blurred vision. Since the inflammation is deep within the eye, it causes a dull ache rather than the superficial irritation of conjunctivitis.
Corneal abrasions and ulcers are injuries or infections on the cornea, the clear dome covering the iris and pupil. An abrasion (scratch) causes a sharp, foreign-body sensation and severe pain that worsens with blinking. A corneal ulcer, often resulting from bacterial infection in contact lens wearers, appears as a whitish spot and can lead to rapid vision deterioration.
A subconjunctival hemorrhage is a benign yet dramatic cause of redness, appearing as a bright red, uniform patch on the white of the eye. This occurs when a small blood vessel breaks beneath the conjunctiva, often due to coughing, straining, or vomiting. Although alarming, this condition typically causes no pain or vision change and resolves spontaneously within one to two weeks as the blood is reabsorbed.
Recognizing Distinct Symptoms and Urgency
The associated symptoms are the most reliable way to distinguish a self-limiting red eye from an urgent medical situation. Conjunctivitis usually involves a gritty or itchy sensation, with pain being mild and localized to the surface. In contrast, deep, intense eye pain, especially if accompanied by a headache or nausea, indicates a serious condition like acute angle-closure glaucoma.
Vision changes are a powerful red flag, as uncomplicated pink eye rarely affects visual acuity. Any sudden blurring, haziness, or partial loss of vision suggests involvement of the cornea or deeper eye structures, such as with uveitis or corneal ulcers. While some light sensitivity can occur with severe pink eye, pronounced photophobia is a defining symptom of uveitis or a corneal injury.
Discharge characteristics also provide differentiation: thick, purulent discharge signals a bacterial infection, while watery discharge is typical of viral or allergic causes. The absence of discharge, coupled with severe pain, light sensitivity, and vision loss, requires immediate medical evaluation. Any red eye associated with severe pain, sudden vision decrease, or the perception of halos around lights requires urgent consultation.