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.