Practicability and Effectiveness of Anterior Segment Optical Coherence Tomography (AS-OCT) of the Feline Iris as a Potential Biomarker for Iris Melanoma: A Study of 76 Cases.

AS-OCT can non-invasively distinguish feline iris melanoma from melanosis with 100% sensitivity in confirmed cases.

This prospective observational study evaluated the practicability and diagnostic utility of anterior segment optical coherence tomography (AS-OCT) for differentiating feline iris melanosis from iris melanoma in 76 client-owned cats. The ZEISS Primus 200 OCT system was used, with most examinations (65/76) performed without anesthesia, demonstrating good patient tolerability. Key quantitative findings revealed that normal and melanosis-affected irides had similar mean iris thickness (~316–319 μm) and preserved architectural layering, whereas suspected and histologically confirmed melanomas exhibited significantly increased iris thickness (~474–593 μm) with posterior signal attenuation and loss of structural detail. Pigmentation-to-normal (PN) ratios were approximately 1.07 in melanosis versus 1.58–1.61 in melanoma cases, providing a potentially useful quantitative threshold. Histopathological confirmation was available in 15 melanoma cases and one melanosis case post-enucleation; all 15 OCT-classified melanomas were confirmed histologically, yielding a diagnostic sensitivity of 100%. The single melanosis case was also correctly classified by OCT. While the study is limited by a small histologically confirmed cohort and absence of specificity data from a larger biopsy-confirmed melanosis group, AS-OCT demonstrates strong potential as a non-invasive, in-clinic biomarker tool. Clinicians may use iris thickness measurements and structural OCT characteristics to guide enucleation decisions in cats with progressive iris pigmentation changes, distinguishing benign melanosis from malignant melanoma without immediate surgical intervention.

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