Iris melanin pigment as a masquerade of Gram-positive cocci after penetrating ocular trauma

We describe a case of penetrating eye injury that resulted in a post-injury day 1 hypopyon, leading to concern for endophthalmitis and phacoanaphylaxis. A Gram stain prepared by the clinical microbiology laboratory was interpreted as Gram-positive cocci (GPC). However, when cultures returned negative, further investigation with microbiology and pathology found that what was thought to be GPC was actually iris melanin pigment. Although endophthalmitis following ocular trauma remains an important diagnosis to consider, this microbiologic masquerade of iris melanin pigment as GPC should be considered in cases where Gram stain is positive yet cultures return negative.