The aqueous VEGF concentration is elevated in various types of glaucoma such as neovascular glaucoma, pseudoexfoliation glaucoma, angle-closure glaucoma, and POAG.12,19,20 The source of VEGF production in glaucomatous eyes is not clear. However, because the VEGF level was elevated in the aqueous humor when compared with the plasma VEGF concentration in patients with glaucoma and no significant correlation was observed between VEGF in the aqueous humor and plasma, VEGF is presumed to be produced locally by ocular cells in glaucoma.19,20 Vascular endothelial growth factor is expressed and produced by the corneal endothelium, iris pigment epithelium, retinal pigment epithelium, retinal ganglion cells, astrocytes, Muller cells, uveal melanocytes, and choroidal fibroblasts.19 Although little is known of the expression and production of VEGF in conjunctival epithelial cells or Tenon fibroblasts, VEGF was elevated in the Tenon tissue of the patients with POAG in our study. The source of the VEGF in Tenon tissue may have been VEGF in the aqueous humor or vitreous cavity by diffusion or from local cells and blood vessels in the subconjunctival space. Because the VEGF in Tenon tissue was not correlated with the VEGF in the aqueous humor, diffusion may not have been the only source of the Tenon VEGF. The turnover time of the aqueous humor is about 100 minutes. This means that after 100 minutes, the anterior chamber is filled with newly produced aqueous humor and the VEGF in the aqueous humor may have passed through the trabecular meshwork pores and reached the Tenon tissue. Consequently, the VEGF in Tenon tissue may not correlate to the VEGF in the aqueous humor, although the VEGF comes from the aqueous humor via diffusion. This rapid turnover rate of VEGF in the aqueous humor may also explain why no relationship was detected between the surgical outcome of glaucoma surgery and the VEGF in the aqueous humor.