Syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum. The infection can spread throughout the body, and when it affects the eyes, the resulting condition is known as ocular syphilis. This serious complication can emerge at any stage of the disease, even without other systemic symptoms. Because ocular syphilis can cause rapid, permanent vision loss, it is considered a medical emergency requiring immediate diagnosis and high-dose antibiotic treatment.
How Syphilis Infiltrates Eye Tissues
The bacterium Treponema pallidum enters the eye through hematogenous spread, traveling from the initial infection site via the bloodstream to reach the eye’s vascularized structures. Once in the ocular environment, the bacteria must breach the blood-retinal barrier, a specialized layer of cells that protects sensitive tissues from circulating pathogens.
The primary target is often the uveal tract, the middle layer containing the iris, ciliary body, and choroid; inflammation here is called uveitis. The infection can also attack the retina, the light-sensitive tissue at the back of the eye, causing retinitis or chorioretinitis. Additionally, the spirochete can infect the vitreous humor, the gel-like substance filling the eyeball, resulting in clouding known as vitritis.
Infection may also involve the optic nerve, which transmits visual information to the brain, leading to optic neuritis. The bacteria and the resulting inflammatory response damage these delicate tissues, interfering with the normal transmission of visual signals.
Recognizing the Specific Symptoms
Ocular syphilis is often called “the great masquerader” because its symptoms mimic numerous other inflammatory and infectious eye diseases. The presentation is highly variable, depending on which part of the eye is affected. Patients typically experience sudden changes in sight, which may be unilateral or affect both eyes.
Visual disturbances are common, frequently presenting as new floaters due to inflammation in the vitreous humor. Blurred central vision may occur if the infection impacts the macula, the part of the retina responsible for sharp sight. Light sensitivity (photophobia), redness, or pain in the eye are frequent complaints signaling an active inflammatory process, such as uveitis.
When the optic nerve is involved, patients may experience a rapid reduction in visual acuity that can quickly progress to blindness without intervention. Physical signs can include inflammation or a rash on the eyelids. A specific finding in late-stage syphilis affecting the nervous system is the Argyll Robertson pupil, where the pupil constricts when focusing on a near object but does not react to light.
Prompt Detection and Diagnostic Procedures
Rapid diagnosis is imperative to prevent permanent vision loss, beginning with a comprehensive eye examination by an ophthalmologist. The specialist looks for characteristic signs of intraocular inflammation or damage to the retina and optic nerve. However, clinical findings alone are insufficient, and laboratory tests are necessary to confirm the diagnosis.
Confirmation relies on serologic testing, typically involving a two-step approach using non-treponemal and treponemal tests. Non-treponemal tests, such as the Rapid Plasma Reagin (RPR) or Venereal Disease Research Laboratory (VDRL) tests, are used for initial screening and to track treatment response, as antibody levels decrease after successful therapy. These are followed by treponemal tests, like the Fluorescent Treponemal Antibody Absorption (FTA-ABS) or Treponema pallidum Particle Agglutination (TPPA) tests, which confirm the presence of antibodies specific to the bacterium.
Since ocular involvement is often classified as a form of neurosyphilis, Cerebrospinal Fluid (CSF) analysis via a lumbar puncture may be performed. Recent guidelines suggest this is not always necessary for isolated ocular symptoms without other neurological signs. This procedure checks for the presence of the bacteria or inflammatory markers in the fluid surrounding the brain and spinal cord. The decision to perform a lumbar puncture is guided by the extent of the patient’s symptoms and the treating physician’s judgment.
Standard Medical Intervention
Once ocular syphilis is diagnosed, treatment must commence immediately, administered according to the Centers for Disease Control and Prevention guidelines for neurosyphilis. The standard regimen is high-dose intravenous (IV) aqueous crystalline penicillin G. This is the only antibiotic proven to consistently achieve adequate levels in the central nervous system and the eye. This medication is administered every four hours or as a continuous infusion for 10 to 14 days.
This intensive protocol is necessary because the eye is an immune-privileged site, making it difficult for standard antibiotic doses to penetrate and eliminate the bacteria. For individuals with a documented penicillin allergy, an alternative is a 10 to 14-day course of intravenous ceftriaxone, though penicillin desensitization is preferred, especially for pregnant patients. Topical corticosteroid drops may also be prescribed to help control the severe inflammation associated with uveitis or retinitis.
Following the antibiotic course, patients require close monitoring, including repeated eye exams and follow-up serologic testing. Non-treponemal test titers are re-checked at regular intervals, typically every three to six months, to confirm a four-fold or greater decrease in the antibody level, indicating a successful therapeutic response. Ongoing monitoring is essential to ensure the infection is completely cleared and to assess the extent of visual recovery.