Conjunctivitis, commonly known as “pink eye,” is inflammation of the conjunctiva, the clear membrane covering the white part of the eye and the inner eyelid. This condition causes the small blood vessels in the conjunctiva to become visible and swollen, giving the eye its characteristic reddish or pink appearance. While many people associate pink eye with a highly contagious infection affecting both eyes, unilateral conjunctivitis—inflammation limited to only one eye—is a distinct diagnostic signal. The initial unilateral presentation suggests the cause is often localized, either due to an external agent or an infection that has not yet spread.
Defining Unilateral Conjunctivitis and Its Symptoms
Unilateral conjunctivitis involves inflammation where only one eye exhibits symptoms such as redness, tearing, or a feeling of grittiness. This sensation is frequently described as if a foreign body is lodged in the eye. The nature of the discharge can offer clues about the underlying cause.
Viral forms of unilateral conjunctivitis typically produce a clear, watery discharge and may involve swelling of the lymph nodes in front of the ear. In contrast, a thick, pus-like discharge—often yellow, white, or green—is more indicative of a bacterial infection, which can cause the eyelids to stick together upon waking. While allergic conjunctivitis most often affects both eyes, localized exposure to an irritant or a specific type of allergy can manifest unilaterally, usually accompanied by intense itching.
Specific Causes of Single-Eye Inflammation
The reason inflammation remains confined to one eye is that the cause is localized, stemming from direct contact with an irritant, a foreign body, or an infection that has not been transferred. Infectious causes can begin unilaterally, especially in the early stages of viral or bacterial pink eye, before a person inadvertently spreads the agent to the other eye via hand contact. More specific localized infections exist, such as Parinaud Oculoglandular Syndrome, a rare condition that presents as granulomatous conjunctivitis in one eye accompanied by noticeable swelling of the adjacent lymph nodes.
Mechanical or irritant factors are also major contributors to a single-eye presentation. A foreign body, such as dust, sand, or a loose eyelash, can become lodged under the eyelid, causing persistent redness and irritation until it is removed. Chemical exposure, ranging from a splash of household cleaner to heavy smoke or fumes, will often affect only the eye that received the direct contact. Contact lens wearers can develop giant papillary conjunctivitis, a localized allergic response to the lens material or deposits on the lens, or may be at risk for a localized corneal infection. An exposed suture from a prior eye surgery can also act as a chronic mechanical irritant, leading to persistent unilateral inflammation.
Treatment Approaches Based on Cause
Effective management of unilateral conjunctivitis is dependent on the accurate identification of the cause. For cases confirmed as bacterial, treatment typically involves topical antibiotic drops or ointments, such as fluoroquinolones, which help resolve the infection and may shorten the duration of symptoms. Contact lens wearers with suspected bacterial infection are often prescribed broad-spectrum antibiotics to cover for organisms like Pseudomonas, given their increased risk for serious corneal complications.
Viral conjunctivitis, which is the most common form, does not respond to antibiotics; instead, management focuses on supportive care. This includes the use of artificial tears to soothe the eye and the application of cold compresses to reduce inflammation and discomfort until the virus runs its course, which can take up to two or three weeks. If the cause is mechanical or irritant-based, the primary treatment is removing the offending agent, such as flushing the eye thoroughly with water after a chemical splash or physically removing a foreign body. Meticulous hygiene is paramount to prevent the spread to the second eye or to other people, requiring frequent handwashing and avoiding sharing towels or pillows.
Warning Signs Requiring Urgent Care
While most cases of pink eye are not serious, certain symptoms require immediate medical consultation to prevent potential vision-threatening complications.
- Severe or intense eye pain that goes beyond the typical gritty or scratchy feeling.
- Sudden changes in vision, such as blurriness or loss of visual acuity, should prompt evaluation, as conjunctivitis rarely affects vision alone.
- Extreme sensitivity to light (photophobia), especially when combined with pain, may indicate that the inflammation has spread to the cornea.
- If symptoms do not begin to improve within 24 to 48 hours, or if the inflammation or discharge rapidly worsens.
People who wear contact lenses and develop any symptoms must stop wearing their lenses immediately and seek prompt care, as they are at a higher risk for rapidly progressive corneal infections.