A histologic survey of trabeculectomy.

Thirty-two tissue blocks removed during trabeculectomy were examined histologically, 16 by both scanning electron microscopy and light microscopy, and 16 by light microscopy alone. Trabecular meshwork was identified in 27 specimens (84.3%) and Schlemm's canal in 17 (53%), each found with equal frequency by either technique. Ciliary muscle was identified in eight of 32 of specimens (25%) examined by light microscopy, but was present in 12 of 16 specimens (75%) examined by scanning electron microscopy. The identification of these specific anatomical structures did not correlate with the postoperative outcome. These findings support the contention that trabeculectomy is a filtering procedure.