Increasing Lymphatic Microvessel Density in Primary Pterygia

OBJECTIVE: To examine lymphatic microvessel density (LMVD) in primary pterygia. METHODS: We included tissue samples from 88 excised primary (including 34 grade 1, 28 grade 2, and 26 grade 3) pterygia and from 7 nasal epibulbar conjunctivae segments used as control samples. Sections from each pterygium were immunostained with CD31 and lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1) monoclonal antibodies to evaluate LMVD and blood microvessel density. We used real-time polymerase chain reaction analysis to measure expression of vascular endothelial growth factor A (VEGF-A) and VEGF-C messenger RNA (mRNA) in the pterygia. RESULTS: A small number of CD31-positive LYVE-1-negative blood vessels and only a few CD31- and LYVE-1-positive lymphatic vessels were detected in the normal epibulbar conjunctiva segments. Lymphatic vessels were mildly increased in grade 1 pterygia but were dramatically increased in grades 2 and 3 pterygia. Lymphatic microvessel density correlated closely with blood microvessel density in grades 1, 2, and 3 pterygia (P < .05 for all). The width and area of pterygia were significantly correlated with LMVD. In addition, we found a significant relationship between VEGF-C mRNA expression and LMVD in grades 1, 2, and 3 pterygia, whereas VEGF-A mRNA expression correlated closely with LMVD only in grade 1 pterygia. CONCLUSIONS: Lymphatic microvessel density increases dramatically in grades 2 and 3 pterygia. Transient upregulation of VEGF-C might be responsible for the occurrence of lymphangiogenesis.