[Evaluation of confocal microscopy in the analysis of the external trabecular membrane during deep nonpenetrating sclerectomy].

Purpose: Deep non penetrating sclerectomy (DNPS) is a new filtering surgical procedure whose aim is a selective ablation of the external portion of the trabecular meshwork (TM) which is involved in the aqueous outflow resistance, i.e. the inner wall of Schlemm's canal (SC) and the external trabecular layers, especially the cribriform TM. We evaluated, with a confocal microscope, the structural characteristics of this part of the TM in glaucomatous patients.

Methods: Thirty-six external trabecular membranes (ETM) were obtained from 33 consecutive glaucomatous patients (mean age: 56.5+/-14.5 years) and from four post-mortem normal donors (60.5 +/-7.7 years), which underwent DNPS according to the same surgical procedure. Under conjunctival and scleral flaps, the roof of the SC was opened and removed. A deeper dissection led to 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 with 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 microm in glaucomatous eyes, not significantly different from the controls (39.0+/-10.7 microm). The main characteristic of the glaucomatous ETM membrane is a paucicellularity as compared to the controls (respectively 21.6+/-12.1 cells/area and 156.1+/-28.8 cells/area). The confocal microscope analysis shows that the ETM involves two different portions of the trabecular meshwork. The architectural characteristics of the outermost portion of the ETM with its star-shaped cells arranged in a homogenous extra-cellular matrix, suggest that it is the trabecular cribriform meshwork. The inner portion of the ETM shows cells arranged regularly in a fibrillar extra-cellular matrix as described in the corneoscleral trabecular meshwork.

Conclusion: These results confirm the previous reported histopathological changes of the glaucomatous TM. The thickness of the removed ETM and its structural characteristics show that the ablation of the TM layers necessary to obtain a satisfactory aqueous filtration, not only involves the cribriform 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 the cribriform trabecular meshwork but also a part of the corneoscleral trabecular meshwork.