The corneal lesion in our patient resulted from an iron foreign body injury, appearing brownish in color, which differed from the typical presentation of fungal keratitis, making it susceptible to misdiagnosis as rust residue. Post-traumatic keratitis has been reported in 55–65% of keratomycosis cases according to previous research [1]. Therefore, it is crucial to acknowledge the potential for fungal infection and remain vigilant.

Phaeoisaria sp. primarily causes plant infections, wheras human infections caused by this fungus are uncommon. Phaeoisaria clematidis mainly infects plants such as Clematis, and only one previous research has reported it as a cause of human keratitis. However, its clinical characteristics and the corneal ulcers have not been fully described [4]. Phaeoisaria sp. is a dark, filamentous fungus with low invasive potential and a high likelihood of lateral growth on the cornea [4]. While previous studies have focused on the etiology, this study pays more attention to the unusual appearance of corneal ulcers and their imaging features.

According to previous studies [3], this species of fungus is known for its high level of resistance, and is likely to be resistant to commonly used antifungal drugs in clinical practice. Given the severity of the patient’s condition, we administered 0.1% amphotericin B eye drops in combination with surgical intervention and the topical application of iodine tinctures. Removing red material from the surface of corneal ulcers provides specimens for pathogen detection and aids in the identification of ferrous foreign bodies. This may enhance the efficacy of topical drug therapy.

In our literature search, previous animal studies indicated that Phaeoisaria clematidis can infect mice, leading to dark nodular lesions across multiple organs. Histological examination revealed that the lesions were characterized by granulomata [5]. However, there is currently no direct evidence of human infection in other organs. Further research is necessary to explore the potential pathogenic mechanisms and clinical relevance of this fungus.

In this case, burn of corneal ulcer with iodine tincture is a traditional anti-infective treatment that is still used in developing countries. Clinical experience suggests that this treatment can shorten the course of fungal keratitis, but further studies are needed to confirm.

In conclusion, this case highlights the importance of considering corneal fungal infection in patients with corneal foreign bodies. Corneal smear and IVCM examination should be conducted for suspected cases with a history of trauma. Therefore, early detection, diagnosis, and treatment of this condition are crucial. Proactive use of antifungal drugs, smear and cauterization of corneal lesions, and applying iodine tincture can effectively manage disease progression.