Diagnostic value of iris biopsies for the assessment of iris pigment changes and diffuse iris melanoma (DIM) in cats: A descriptive histopathological study

Feline diffuse iris melanoma (FDIM) is a common ocular neoplasm, typically affecting older cats, characterized by progressive hyperpigmentation and potential malignancy. This study evaluated the diagnostic value of iris biopsies in distinguishing FDIM from benign iris melanosis. Seventeen cases with suspected FDIM were analyzed through ex vivo iris biopsies and corresponding enucleated globes. Histological evaluation by 8 pathologists revealed an average concordance of 81.6% between biopsy and globe diagnoses. The reliability of biopsy samples was influenced by tissue quality, with 12/136 slides deemed non-diagnostic due to artifacts or insufficient tissue. While biopsy retrieval offers a less invasive alternative to enucleation, its effectiveness is limited by technical factors, including tissue handling and sampling techniques. The results suggest that iris biopsies can be valuable for diagnosing advanced FDIM but require skilled execution. Further studies should explore early-stage FDIM and melanosis to better assess the diagnostic potential of biopsies across various disease stages.