Syphilis is a systemic infection caused by the bacterium Treponema pallidum. While widely recognized as a sexually transmitted infection, the bacteria can travel through the bloodstream and affect nearly any organ in the body. When the infection involves the eye, it is termed ocular syphilis, a condition that poses a significant risk to vision. This eye involvement can occur at any stage of the infection, and without prompt and effective treatment, it can lead to irreversible vision loss.
How Syphilis Reaches and Damages Eye Structures
The bacteria Treponema pallidum gains access to the eye through the circulatory system following the initial infection, a process known as hematogenous spread. Once the spirochetes disseminate throughout the body, they directly invade ocular tissues, triggering an inflammatory response that causes damage. Ocular syphilis can manifest during any of the infection’s stages—primary, secondary, latent, or tertiary—and is frequently seen in the secondary stage when the bacteria is actively spreading.
The most susceptible structures within the eye include the uveal tract, the retina, and the optic nerve. The inflammation caused by the bacteria and the body’s immune reaction leads to tissue destruction in these areas. Because the eye is considered an extension of the central nervous system, ocular syphilis is treated with the same urgency as neurosyphilis, a classification that dictates the choice of antibiotic therapy.
Specific Eye Manifestations of Ocular Syphilis
Ocular syphilis symptoms can resemble those of many other eye diseases, making diagnosis challenging. The most common manifestation is uveitis, which is inflammation of the uvea (the middle layer of the eye comprising the iris, ciliary body, and choroid). Uveitis can present as anterior, intermediate, or posterior uveitis.
Posterior uveitis and panuveitis (involving all parts of the uveal tract) are the most frequent presentations in immunocompetent adults. Symptoms of uveitis include eye pain, redness, sensitivity to light, and blurred vision. When the infection reaches the back of the eye, it causes retinitis, which is inflammation of the retina.
Retinitis often presents as chorioretinitis, affecting both the retina and the underlying choroid, resulting in vision loss, floaters, and sometimes retinal detachment. Damage to the optic nerve (optic neuropathy or optic neuritis) is a serious manifestation that can cause rapid vision loss. Less common manifestations include interstitial keratitis (corneal inflammation), retinal vasculitis (inflamed blood vessels), and acute syphilitic posterior placoid chorioretinopathy, which involves plaques of inflammation at the back of the eye.
Identifying Ocular Syphilis and the Need for Immediate Action
Diagnosis begins with a comprehensive eye examination to identify specific signs of inflammation, such as uveitis, retinitis, or optic nerve swelling. Since the presentation can mimic many other conditions, a high degree of clinical suspicion is necessary in any unexplained case of ocular inflammation.
Laboratory testing follows the eye exam using blood tests to detect syphilis antibodies. These serologic tests include non-treponemal tests (such as the Rapid Plasma Reagin or VDRL tests) and treponemal-specific tests. A reactive result confirms the presence of systemic syphilis infection.
Because ocular syphilis is treated as a form of neurosyphilis, a cerebrospinal fluid (CSF) analysis may be indicated to check for central nervous system involvement. This analysis is obtained via a lumbar puncture (spinal tap) and involves testing the CSF for syphilis antibodies and signs of inflammation. Current guidelines may waive this requirement if the patient has no neurological symptoms and is not co-infected with HIV. Rapid diagnosis is paramount because any delay in treatment increases the risk of permanent vision loss due to irreversible damage to the retina and optic nerve.
Treatment Protocols and Post-Therapy Monitoring
The standard treatment for ocular syphilis is high-dose antibiotic therapy using aqueous crystalline penicillin G. Penicillin remains the drug of choice because it is highly effective against Treponema pallidum and penetrates the central nervous system and eye tissues.
The medication is administered intravenously (IV) for 10 to 14 days. The IV route is favored over oral or intramuscular administration to ensure consistently high concentrations of the antibiotic reach the eye and central nervous system to eradicate the bacteria. Alternative regimens, such as intramuscular penicillin G combined with oral probenecid, or ceftriaxone, may be used if IV penicillin G is not feasible or in cases of penicillin allergy.
Post-therapy monitoring is required to confirm the infection has cleared. Follow-up involves repeat serologic blood tests, typically the RPR or VDRL, at regular intervals such as six and twelve months after treatment. The goal is a fourfold decrease in the antibody titer, which indicates a successful response. Ongoing eye examinations are also essential to monitor vision improvement and detect any relapse.