The human anterior segments were fixed in paraformaldehyde, 1%, and cut meridionally into 1 block/quadrant, yielding 4 blocks per eye, with each block measuring 1.5 mm in width. Each dissected block included the entire aqueous outflow pathway, as well as some peripheral cornea and adjacent ciliary body and iris tissues. The tissue blocks were embedded in glycol methacrylate and were cut into step-serial sections, each measuring 2 μm in thickness and separated from each other by a step measuring 25 μm, yielding 60 step-serial sections per block/quadrant and 240 step-sections per eye. Each section was exposed to anti-CD68 antibody (Zymed, San Francisco) for the purpose of counting CD68+ cells on a Zeiss ultraphotomicroscope (Zeiss, Thornwood, New York) since CD68 is a marker specific for monocytes. The monkey specimens were fixed in paraformaldehyde, 1%/glutaraldehyde, 2%, solution and embedded in Araldite adhesive (Huntsman Advanced Materials, Salt Lake City, Utah). The tissue blocks from the monkeys were also cut into sections of 2 μm in thickness, spaced at 25-μm intervals, with 60 step-serial sections per block, and they were stained with Richardson methylene blue. Using a Zeiss ultraphotomicroscope, each of the 60 sections per block was inspected and the mononuclear cells were counted as representing monocytes. For the human and monkey specimens, the mean monocyte count and the standard deviation per 60 samples for each of the examined blocks was determined. For the studies on the transit of monocytes through the monkey eye, the monocytes recruited to the anterior chamber after SLT and labeled in vivo by the nuclear-localizing β-galactosidase transduction construct were stained with the β-galactosidase substrate X-gal (Invitrogen, Carlsbad, California) and/or anti-CD68 antibody.