Syphilis, caused by the bacterium Treponema pallidum, can affect almost any organ system. When the infection spreads to the eye, it is known as ocular syphilis, a serious manifestation that can lead to permanent vision loss if not promptly treated. Ocular syphilis can occur at any stage of the disease, even the latent phase when other symptoms are absent. Because the organism invades the nervous system, ocular syphilis is classified as a form of neurosyphilis, requiring an aggressive treatment approach.
How Syphilis Affects Different Eye Structures
Ocular syphilis is often referred to as “the great imitator” because its symptoms can closely resemble those of many other inflammatory eye conditions. The infection can involve nearly every structure within the eye, but it most frequently targets the uvea, the middle layer of the eye. Inflammation of this layer is called uveitis, and it is the most common manifestation seen in ocular syphilis.
Uveitis can be further categorized based on the specific part of the uvea affected, such as the iris, ciliary body, or choroid. Inflammation in the posterior section, known as posterior uveitis or panuveitis, is particularly common and often presents with blurred vision and the appearance of floaters. These floaters are inflammatory cells and debris suspended in the vitreous gel.
Another severe complication is the inflammation of the retina (retinitis) or the retina and its underlying vascular layer (chorioretinitis). This deep-seated inflammation can cause sudden, significant vision loss and damage the light-sensitive tissues at the back of the eye. The organism can directly invade the retina, causing a characteristic appearance on examination that suggests the diagnosis.
The optic nerve, which transmits visual information from the eye to the brain, is also vulnerable to the infection, resulting in optic neuritis or optic neuropathy. Inflammation of this nerve can lead to a rapid reduction in visual acuity and, if left untreated, irreversible blindness. Damage to this nerve is a direct sign of central nervous system involvement.
Less common manifestations affect the anterior structures of the eye. These include interstitial keratitis, a non-ulcerative inflammation of the cornea (the clear front window of the eye). This corneal inflammation can cause light sensitivity, pain, and a cloudy appearance. Rarely, a painless sore (chancre) can appear on the eyelid or conjunctiva.
Confirming the Presence of Ocular Syphilis
The diagnosis of ocular syphilis relies on a combination of a thorough eye examination and specific laboratory testing. A specialist will perform a comprehensive ocular evaluation using instruments like a slit lamp and ophthalmoscope to visualize the inflammation and damage in the anterior and posterior segments of the eye. This examination helps to identify characteristic signs, such as inflammatory cells in the vitreous or specific retinal lesions.
Serological blood tests are essential for confirming the presence of a syphilis infection. These tests are divided into two main types: non-treponemal and treponemal assays. Non-treponemal tests, such as the Rapid Plasma Reagin (RPR) and Venereal Disease Research Laboratory (VDRL) tests, are used for screening and provide a quantitative titer that can be monitored to track the patient’s response to treatment.
Treponemal tests, including the Fluorescent Treponemal Antibody Absorption (FTA-ABS) and the Treponema pallidum Particle Agglutination (TP-PA) assays, are highly specific and confirm the infection. They detect antibodies specific to the Treponema pallidum bacterium, which usually remain positive for life, even after successful treatment. Both types of tests are typically used together to accurately diagnose the infection.
Because ocular syphilis is classified as neurosyphilis, cerebrospinal fluid (CSF) analysis, often called a lumbar puncture or spinal tap, is frequently required. This procedure involves collecting fluid surrounding the brain and spinal cord to check for evidence of infection. The analysis looks for an elevated white blood cell count, increased protein, or a reactive VDRL test directly in the CSF.
However, CSF analysis is not always necessary for every patient presenting with ocular symptoms. If a patient has isolated ocular symptoms with reactive syphilis serology but no evidence of cranial nerve dysfunction or other neurologic signs, treatment can often be started without a lumbar puncture. A full neurologic examination is always performed to rule out broader central nervous system involvement.
The Urgent Nature of Treatment
Treating ocular syphilis requires immediate and aggressive intervention to prevent permanent vision loss. The treatment protocol is the same as that for neurosyphilis, demanding high-dose antibiotics to ensure the medication crosses the blood-brain and blood-retinal barriers effectively. Penicillin remains the only drug with proven efficacy against Treponema pallidum for neurosyphilis.
The standard regimen involves administering aqueous crystalline penicillin G intravenously for a duration of 10 to 14 days. The typical dosing is 18 to 24 million units per day, often given as a continuous infusion or divided into doses every three to four hours. This intensive regimen usually requires the patient to be admitted to a hospital for the entire course of treatment.
For patients who have a documented, non-life-threatening allergy to penicillin, alternatives such as ceftriaxone are sometimes considered. However, medical guidelines strongly recommend that patients undergo desensitization, as penicillin is the only treatment with sufficient evidence to cure neurosyphilis.
Following the completion of the intravenous course, regular follow-up is necessary to monitor the patient’s response to the antibiotic. This monitoring typically involves repeating the non-treponemal blood test (RPR or VDRL) to ensure the titer has decreased significantly, which indicates a successful therapeutic response. A fourfold drop in the titer is generally expected within six to twelve months after treatment.