Ocular syphilis is a complication of the sexually transmitted infection (STI) syphilis, which is caused by the bacterium Treponema pallidum. This condition occurs when the infection spreads through the bloodstream to the eyes, causing inflammation and damage to sensitive ocular structures. Untreated ocular syphilis can quickly lead to severe vision loss and even permanent blindness, demanding immediate medical attention. Understanding how the initial syphilis infection is acquired helps recognize the risk of this serious eye complication.
How the Syphilis Infection is Acquired
The bacterium Treponema pallidum cannot survive long outside a host, meaning its transmission requires close physical contact. Syphilis is primarily acquired through direct contact with an infectious sore, known as a chancre, during sexual activity. This includes vaginal, anal, and oral sex, where the bacteria penetrate the skin or mucous membranes at the site of contact.
The chancre typically appears during the primary stage of syphilis and is often painless, allowing the infection to be spread unknowingly. The infection is highly contagious during the primary and secondary stages when these sores or a widespread rash are present. Transmission can also occur from a pregnant person to their fetus during gestation, resulting in congenital syphilis.
When Syphilis Spreads to the Eyes
Ocular syphilis represents the internal migration of the Treponema pallidum pathogen through the bloodstream. After entering the body, the spirochete can disseminate to virtually any organ system, including the central nervous system (CNS). Ocular syphilis is often considered a form of neurosyphilis because the optic nerve is an extension of the CNS.
The spread to the eye can happen at any stage of the syphilis infection—primary, secondary, latent, or tertiary—but is most frequently observed during the secondary stage. During this phase, the widespread bacteria can inflame ocular tissues and cause conditions like uveitis, retinitis, and optic neuropathy. Uveitis, inflammation of the eye’s middle layer, is the most common manifestation and can severely impair vision. Ocular symptoms can sometimes appear even after generalized systemic symptoms have resolved, making diagnosis challenging.
Who is Most at Risk
The risk of developing ocular syphilis is directly linked to behaviors that increase the risk of acquiring syphilis, such as having multiple sexual partners or engaging in unprotected sex. A significant factor that elevates the risk is co-infection with the Human Immunodeficiency Virus (HIV), and increasing incidence has been noted in specific demographic groups, including men who have sex with men (MSM).
Individuals living with HIV are almost twice as likely to develop ocular syphilis compared to those who are HIV-negative. This increased vulnerability is pronounced in HIV-positive patients who have an unsuppressed viral load or a low CD4 cell count, indicating a weakened immune system. Therefore, any patient presenting with eye inflammation should be tested for both syphilis and HIV to account for this heightened risk.
Treatment and Prevention
Diagnosis involves a comprehensive eye examination and specific serological blood tests to confirm the presence of Treponema pallidum antibodies. Because the infection has spread to the eye, it is treated aggressively like neurosyphilis, requiring a more intense regimen than standard syphilis. The treatment of choice is high-dose aqueous crystalline penicillin G administered intravenously, typically for 10 to 14 days, often necessitating hospitalization.
This intravenous treatment ensures adequate concentrations of the antibiotic reach the central nervous system and the eye. For those with severe eye inflammation, topical or oral steroids may be used alongside antibiotics to control swelling. Preventing ocular syphilis relies on preventing the initial infection through safe sex practices, including consistent condom use, and regular screening for high-risk individuals to stop systemic spread.