Sampling trabecular meshwork using TrabEx

Abstract

Background: To report sampling of the trabecular meshwork using the TrabEx+ (MicroSurgical Technology, Redmond, Washington, USA) device in ab interno trabeculectomy. Specifically, this series focusses upon preservation of the trabecular meshwork architecture for assessment of glaucomatous features using common histopathological techniques.

Patients: This series features six glaucomatous eyes undergoing TrabEx+ with or without cataract surgery. Three patients had primary open angle glaucoma and the remaining had pigment dispersion glaucoma, ocular hypertension or uveitic glaucoma. Four eyes had simultaneous cataract surgery.

Methods: Trabecular meshwork was excised using the TrabEx+ device and retrieved using vitreoretinal forceps. The samples were then processed into formalin-fixed paraffin-embedded 4 micron tissue segments and stained with haematoxylin and eosin, periodic acid-Schiff and elastin Van Gieson. Collagen IV was labelled using immunohistochemistry for the purpose of identifying the basement membrane of trabecular beams.

Results: Presence of trabecular meshwork was confirmed in five of the six samples taken. One of six samples consisted of blood only, but this was expected following early termination of the procedure due to patient restlessness. In the five positive cases trabecular beams with associated trabecular meshwork cells were identified on hematoxylin-eosin and periodic acid-Schiff staining. The beams retained their lamellar structure. The basement membrane underlying the trabecular cells was evident in three specimens, whilst two specimens were of insufficient size for collagen IV labelling.

Conclusions: This case series illustrates that TrabEx+ can be utilised to successfully retrieve trabecular meshwork samples with sufficient architectural perseveration of the tissue to enable histopathological and laboratory analysis.

Keywords: Ab interno trabeculectomy; Histology; Tissue sampling; TrabEx+; Trabecular meshwork.

Fig. 1

a-Haematoxylin and Eosin (H&E) stained section of trabecular meshwork. The arrow points to compressed trabecular beams. The asterisk indicates the spaces created by dispersion of the trabecular beams from surgical sampling. b-Periodic acid-Schiff (PAS) stain of the trabecular meshwork. The beams are stained pink. The arrow points to a layer of darker pink material on the trabecular beams indicating trabecular meshwork cell basement membrane. c-PAS stain showing the presence of Descemet’s membrane exhibiting Hassall-Henle excrescences. d-H&E stained trabecular meshwork from eye number 6 with pigment dispersion glaucoma. Note the dark brown pigment deposited on the trabecular beams (arrow). e-Elastin Von Gieson stain of trabecular meshwork showing patchy elastin presence (arrows point to black linear elastin). f-Collagen IV immunohistochemistry. The arrow points to tram track linear staining (brown-positive) over the beams.