An STI affecting the eye usually shows up as intense redness, swelling of the eyelids, and discharge that can range from watery to thick yellow-green, depending on which infection is involved. Several sexually transmitted infections can reach the eyes, either through direct contact with infected fluids or, in the case of syphilis, through the bloodstream. Each one looks and feels somewhat different, and some are far more urgent than others.
Gonorrhea: The Most Visually Dramatic
Gonococcal conjunctivitis is hard to miss. It produces heavy, thick yellow-green discharge that can accumulate rapidly, sometimes causing the eyelids to swell so much they resemble a severe allergic reaction or even a skin infection around the eye. The eyelids may become puffy and difficult to open, and the white of the eye turns deeply red. Lymph nodes in front of the ear on the affected side often swell as well.
Symptoms typically appear 3 to 19 days after the bacteria reach the eye, with an average incubation of about 6 days. What makes gonorrhea in the eye particularly dangerous is how quickly it can damage the cornea, the clear front surface of the eye. Without treatment, the cornea can thin, develop holes, or even perforate, potentially leading to permanent blindness. This is one of the few eye infections that qualifies as a true emergency.
Chlamydia: Subtler but Persistent
Chlamydial conjunctivitis looks less alarming than gonorrhea but tends to linger for weeks. The hallmark sign is small, raised bumps called follicles on the inner surface of the eyelids and on the white of the eye near the inner corner. These follicles give the tissue a bumpy, cobblestone-like texture that a doctor can see by pulling the lower lid down.
Discharge is typically milder, ranging from a thin mucus to a slightly cloudy, sticky fluid. You might notice your lashes crusting together in the morning or your lids feeling “glued shut” after sleep. The eye looks pink or red, but the swelling is usually less severe than with gonorrhea. Because the symptoms are relatively mild, people often mistake chlamydial eye infections for a stubborn case of pink eye and delay getting tested, which allows the infection to persist and potentially scar the inner eyelid over time.
Herpes (HSV): Corneal Ulcers and Blisters
Herpes simplex virus affects the eye differently from the bacterial STIs. The first episode may look like a mild case of conjunctivitis with watery discharge and redness, sometimes accompanied by small blisters or ulcers on the eyelid skin. What sets herpes apart is what happens on the cornea.
The virus creates a distinctive branching ulcer on the corneal surface called a dendritic ulcer. It starts as tiny scattered dots on the cornea that merge into a tree-branch pattern. These ulcers are often centrally located and have characteristic bulb-shaped endings at each branch tip. You can’t see them with the naked eye, but you’ll feel them: herpes keratitis typically causes sharp pain in one eye, sensitivity to light, blurred vision, and tearing. It almost always affects just one eye, which helps distinguish it from allergic or viral pink eye that tends to hit both.
If the infection recurs or goes untreated, the ulcers can expand into larger, irregular “map-shaped” patches on the cornea, eventually causing scarring that permanently clouds vision.
Syphilis: Deeper Inside the Eye
Ocular syphilis is the outlier in this group because it often doesn’t look like a surface eye infection at all. Instead of causing obvious redness and discharge, syphilis tends to attack structures deeper inside the eye. The most common presentation is inflammation of the middle and back layers of the eye (uveitis), which you’d experience as blurred vision, floaters, and sensitivity to light rather than the crusty, discharge-heavy appearance of gonorrhea or chlamydia.
The CDC notes that ocular syphilis can involve almost any eye structure, including the optic nerve and retinal blood vessels. It can occur during any stage of syphilis infection, meaning it may show up years after the original infection. The outer appearance of the eye might look only mildly red or even normal, while significant damage is happening internally. This makes it easy to overlook, and delayed treatment can result in permanent vision loss.
How These Infections Reach the Eye
The most common route is touching the eye after contact with infected genital or oral fluids. This can happen during sex, especially oral-to-eye or genital-to-eye contact, or simply by touching your face with contaminated hands. Gonorrhea and chlamydia both spread this way. Newborns can also pick up these infections during delivery if the mother has an active genital infection, which is why hospitals apply antibiotic ointment to newborns’ eyes at birth.
Syphilis works differently. The bacteria travel through the bloodstream and can settle in the eye without any direct contact between infected fluids and the eye itself. Herpes can reach the eye through direct contact or by reactivating from a dormant infection in nearby nerve tissue, which is why herpes keratitis often recurs in the same eye.
How Eye STIs Are Diagnosed
A standard eye exam can raise suspicion based on the pattern of redness, discharge, and tissue changes, but confirming which STI is responsible requires laboratory testing. The doctor will typically swab the inside of the lower eyelid and send the sample for a DNA-based test (PCR) that can detect even tiny amounts of chlamydia or gonorrhea bacteria. PCR testing is highly sensitive and can identify as few as 10 bacterial particles in a sample, making it far more reliable than older methods that required a technician to visually hunt for bacteria under a microscope.
For syphilis, diagnosis usually involves a blood test rather than an eye swab, since the infection reaches the eye through the bloodstream. Herpes keratitis is often diagnosed based on its distinctive branching ulcer pattern, which becomes visible when the doctor applies a fluorescent dye to the cornea and examines it under blue light.
What Treatment Looks Like
Bacterial eye STIs (gonorrhea and chlamydia) are treated with antibiotics. Gonorrhea in the eye is treated aggressively because of how quickly it can damage the cornea. Chlamydial eye infections require oral antibiotics taken over a course of days rather than just eye drops, since the bacteria live inside cells where topical treatments can’t easily reach. Sexual partners need treatment at the same time to prevent reinfection.
Herpes keratitis is managed with antiviral medication, and because the virus remains dormant in nerve tissue, some people need long-term preventive antiviral therapy to reduce the frequency of flare-ups. Ocular syphilis requires the same intensive antibiotic treatment used for syphilis that has reached the nervous system.
The most important factor across all of these infections is speed. Gonorrhea can threaten the cornea within days. Chlamydia can scar the eyelid lining over weeks. Syphilis can silently erode vision over months. Herpes can leave permanent corneal haze after repeated episodes. Any persistent red eye with unusual discharge, vision changes, or light sensitivity, particularly if you have a known STI or recent sexual exposure, warrants prompt evaluation rather than a wait-and-see approach.