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Confocal microscopic examination of trabecular meshwork removed during ab externo trabeculectomy

¹ Department of Ophthalmology, Quinze-Vingts Hospital Paris, University Paris V, France
² Laboratory of Toxicology, University Paris V, France
³ Sourdille Ophthalmology Clinical Center Nantes, France
⁴ Department of Ophthalmology, Hotel Dieu Hospital Paris, AP-HP, University Paris VI, France

Correspondence to:
Correspondence to:
Pascale Hamard, MD, Department of Ophthalmology, Quinze-Vingts Hospital, 28 rue de Charenton, 75012 Paris, France;
pascale-hamard{at}quinze-vingts.fr

Aims: The aim of the ab externo trabeculectomy (AET) is to remove the external portion of the trabecular meshwork (ETM) responsible for the main aqueous outflow resistance in glaucoma patients, with no opening of the anterior chamber. ETM characteristics were evaluated with a confocal microscope.

Methods: A prospective comparative observational case series was performed in 60 consecutive medically treated patients with primary open angle glaucoma and eight postmortem normal donors’ eyes that underwent AET. Once deroofing the Schlemm’ s canal (SC), a deeper dissection led to removal of a coherent membrane (ETM) which allowed satisfactory aqueous egress through the remaining intact internal trabecular meshwork (TM) layers. After fixation with acetone and immunostaining with anti-vimentin antibody, ETM were analysed with a confocal microscope.

Results: Glaucomatous ETM (mean thickness: 29.5 (7.6) µm) were characterised by a severe paucicellularity compared with the controls (respectively 37.3 (9.7) cells/area and 167.5 (24.9) cells/area, p<10^-4). ETM analysis showed involvement of both cribriform and corneoscleral layers. ETM cell density was significantly decreased in case of preoperative fluorometholone instillation.

Conclusion: Paucicellularity of glaucomatous TM is confirmed by this original technique. Structural characteristics of the ETM, whose removal allows satisfactory aqueous egress, suggest that aqueous outflow resistance not only involves inner wall of SC and juxtacanalicular meshwork but also corneoscleral trabecular layers.

Keywords: ab externo trabeculectomy; confocal microscopy; trabecular meshwork

Abbreviations: AET, ab externo trabeculectomy; CM, confocal microscope; ETM, external trabecular membrane; FI, fluorometholone instillation; IOP, intraocular pressure; SC, Schlemm’s canal; TEM, transmission electron microscopy; TM, trabecular meshwork