Role of Immunohistochemistry in Orbital Lymphoma:A Diagnostic Review

Orbital lymphoma, a malignant tumour of the orbit, is consistent with a significant proportion of primary and secondary orbital malignancies. Most orbital and ocular adnexal lymphomas are B-cell non-Hodgkin lymphomas, primarily extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT), follicular lymphoma, mantle cell lymphoma, and diffuse large B-cell lymphoma (DLBCL). Benign cases such as reactive lymphoid hyperplasia (RLH), IgG4-related disease (IgG4-RD), and inflammatory lesions may closely mimic lymphoma. Accurate diagnosis is challenging due to overlapping clinical findings and histological similarities. Diagnosing these cases requires integrating clinical findings, imaging, histomorphology, immunohistochemistry (IHC), flow cytometry, and clonality studies. Immunohistochemistry (IHC) has emerged as an indispensable diagnostic tool,enabling precise lineage determination, subtyping, and prognosis. This review summarises the practical role and limitations of IHC in orbital lymphoma, emphasising common ocular adnexal lymphoma subtypes and their differential diagnosis. J.Natl.Inst.Ophthalmol.2025;8(1): 82-84