Carotid cavernous fistula (CCF) is a pathological condition where an abnormal connection forms between the carotid artery and the cavernous sinus. This condition can lead to a variety of ocular and neurological symptoms, often making it difficult to diagnose, especially when patients present with common ocular complaints such as red eye, which is often misdiagnosed as conjunctivitis. The subtle and diverse symptoms of CCF can lead to misdiagnosis, delaying appropriate treatment. This article reports a case of CCF that initially presented with red eye and proptosis, leading to an ophthalmology referral. By comparing pre- and postoperative ocular photographs, the article provides a detailed review of the ophthalmic features, classification, diagnostic methods, and treatment options for CCF. The aim is to enhance clinicians’ understanding of this condition, improve diagnostic accuracy at initial presentation, and promote timely and effective treatment.

A 52-year-old man presented to the ophthalmology department with a 3-month history of left eye redness and proptosis (Figure 1A). The patient reported no history of trauma or systemic diseases. Ophthalmic examination revealed significant tortuosity and dilation of conjunctival veins, particularly prominent in the nasal area (Figures 1C,E). Mild left eye proptosis was noted, but visual acuity and ocular motility were relatively intact. Intraocular pressure was within normal limits. Given the clinical findings, a cranial computed tomography was performed, which suggested a suspected a left carotid cavernous sinus fistula (Figures 2A,B). The patient was subsequently referred to the neurosurgery department for further management.

The patient was diagnosed with carotid cavernous sinus fistula. Subsequently, the patient underwent endovascular embolization, during which a detachable balloon was used to occlude the fistula. Post-procedure, the patient’s left eye proptosis improved significantly, and the conjunctival dilation and edema were notably alleviated (Figures 1B,D,F). Follow-up examinations at 1 month and 3 months post-treatment showed no recurrence of symptoms, and the patient remained asymptomatic.

CCF presenting with red eye can be easily overlooked or misdiagnosed, leading to delayed treatment and potential complications. Clinicians should maintain a high index of suspicion when encountering patients with unexplained ocular symptoms, especially those with persistent red eye accompanied by other ocular abnormalities. Timely utilization of appropriate imaging modalities and referral for further evaluation can significantly enhance diagnostic accuracy and ensure prompt treatment, thereby preventing potential visual impairment and neurological complications. Through this case report and comprehensive review, we aim to raise clinicians’ awareness and understanding of CCF, facilitating early and accurate diagnosis in clinical practice.