To report a case of acute interstitial keratitis as the first clinical sign in a patient with latent syphilis.

A 23-year-old female presented with visual impairment and discomfort in her right eye that developed 3 days earlier. The visual acuity in the right eye was 20/200 and corrected to 20/100, and slit lamp examination showed round sub-epithelial opacification in the central cornea with stromal edema and neovascularization on the cornea of the right eye. Whole body tests including serological tests were performed. Under the suspicion of acute interstitial keratitis, topical antibiotics and steroids were applied 4 times a day initially. Serological tests were reactive for venereal disease research laboratory test (VDRL). Under the suspicion of acute interstitial keratitis due to syphilis, fluorescent treponemal antibody absorption test IgM/IgG (FTA-ABS IgM/IgG) was performed; a positive result for FTA-ABS IgG led to diagnosis of acute interstitial keratitis with latent syphilis. During treatment, systemic doxycycline 200 mg for 4 weeks with topical antibiotics and steroids were administered, the opacity and edema of the cornea regressed after 2 weeks of treatment, and visual acuity in the patient's right eye improved to 20/20.

We report an unusual case of acute interstitial keratitis as the first clinical manifestation of latent syphilis in an immunocompetent patient.