Glycosaminoglycan stratification of the juxtacanalicular tissue in normal and primary open-angle glaucoma

Purpose. The juxtacanalicular tissue (JCT) is the probable site of aqueous outflow resistance in normal eyes and of the increased resistance in primary open-angle glaucoma eyes (POAG). The purpose of this histochemical study was to determine the glycosaminoglycan (GAG) composition and stratification in the JCT of POAG and age-matched normal eyes. Methods. Five eyes from four normal donors and five eyes from four POAG donors (69 to 80 years of age) were analyzed. Using methods that histochemically preserve GAGs, GAG-degrading enzymes, Alcian blue staining, and real color discrimination to exclude pigment, nuclear staining and unstained areas, the type and amount of GAGs were estimated by computer-aided charge-coupled device color video image analysis. To examine GAG stratification, the JCT was segmented into three regions-anterior, middle, and posterior-to examine regional differences in GAG composition: each region was further divided into four 2-μm layers, from layer 1, adjacent to and including the endothelium of Schlemm's canal, to layer 4, to the first trabecular lamellae. Results. The normal GAG JCT profile was as follows: hyaluronic acid (HA), 7.78 ± 1.23 femtograms (fg)/μm₂; chondroitin sulfates (CS), 8.18 ± 0.82 fg/μm₂; dermatan sulfate, 0.29 ± 0.18 fg/μm₂; the total, 18.73 ± 0.68 fg/μm₂. In contrast, the POAG GAG JCT profile was as follows: HA 0.57 ± 0.31 fg/μm₂ (P < 0.00001), a 93% decrease; CS 13.49 ± 0.74 fg/μm₂ (P < 0.0001), a 83% increase; dermatan sulfate, 0.90 ± 0.53 fg/μm₂, and the total, 17.31 ± 0.95 fg/μm₂, an 8.2% decrease. The HA was depleted in all layers of all regions of POAG JCT. Conclusions. Results indicate that the normal JCT is stratified, with HA as the predominant GAG in layers 1 and 2. The POAG JCT is depleted of HA and has an accumulation of CS, which may increase outflow resistance and, consequently, increase intraocular pressure in patients with POAG.