Deep non penetrating sclerectomy with external trabeculectomy. An evaluation with the confocal microscope

Purpose: Deep non penetrating sclerectomy (DNPS) is a new filtering surgica l procedure whose aim is a selective ablation of the external portion of th e trabecular meshwork (TM) which is involved in the aqueous outflow resista nce, i.e, the inner wall of Schlemm's canal (SC) and the external trabecula r layers, especially the cribriform TM. We evaluated, with a confocal micro scope, the structural characteristics of this part of the TM in glaucomatou s patients. Methods: Thirty-six external trabecular membranes (ETM) were obtained from 33 consecutive glaucomatous patients (mean age: 56.5 +/- 14.5 years) and fr om four post-mortem normal donors (60.5 +/- 7.7 years), which underwent DNP S according to the same surgical procedure. Under conjunctival and scleral flaps, the roof of the SC was opened and removed. A deeper dissection led t o the removal of the inner wall of the SC and the adjacent ETM, i.e the TEM , which allowed a satisfactory aqueous flow through the remaining internal TM layers. After fixation with acetone or triton X100 and immunostaining wi th anti-fibronectin or vimentin antibodies, the samples were analyzed with a confocal microscope (Nikon EZ 2000). Results: The mean thickness of the ETM was 34.4 +/- 7.3 mum in glaucomatous eyes, not significantly different from the controls (39.0 +/- 10.7 mum). T he main characteristic of the glaucomatous ETM membrane is a paucicellulari ty as compared to the controls (respectively 21.6 +/- 12.1 cells/area and 1 56.1 +/- 28.8 cells/area). The confocal microscope analysis shows that the ETM involves two different portions of the trabecular meshwork. The archite ctural characteristics of the outermost portion of the ETM with its star-sh aped cells arranged in a homogenous extracellular matrix, suggest that it i s the trabecular cribriform meshwork. The inner portion of the ETM shows ce lls arranged regularly in a fibrillar extra-cellular matrix as described in the corneoscleral trabecular meshwork. Conclusion: These results confirm the previous reported histopathological c hanges of the glaucomatous TM. The thickness of the removed ETM and its str uctural characteristics show that the ablation of the TM layers necessary t o obtain a satisfactory aqueous filtration, not only involves the cribrifor m layers but also one of the inner parts of the TM, i.e. the corneoscleral TM. This result suggests that aqueous humor resistance not only involves th e cribriform trabecular meshwork but also a part of the corneoscleral trabe cular meshwork.