Comparisons of Schlemm's canal and trabecular meshwork morphologies between juvenile and primary open angle glaucoma

Abstract

The histologic differences in Schlemm's canal (SC) and trabecular meshwork (TM), obtained from the trabeculectomy specimens of different age-group glaucoma patients, were compared. This study involved 44 trabeculectomy specimens of 37 juvenile-onset open-angle glaucoma (JOAG) patients (Group A) and 24 trabeculectomy specimens of 24 elderly-onset primary OAG (POAG) patients (age range: 70-79 years, Group B) with no familial history of POAG. Clinical parameters of gender, maximum intraocular pressure (IOP), and the number of glaucoma medications used prior to trabeculectomy were investigated and compared between the two groups. From light microscopy photographs of hematoxylin-eosin, and immunohistochemical staining of markers for SC endothelium (SCE), the total SC length (TSC), comprised of the opened-SC length (OSC) and the closed-SC length (CSC), the percentage of CSC in TSC (%CSC), the percentage of positive SCE marker in CSC (%PinCSC), and the percentage of negative SCE marker in OSC (%NinOSC) were analyzed. Moreover, podoplanin staining patterns in the TM were investigated and compared between the two groups. Among the clinical parameters, the mean maximum IOP in Group A (33.41 ± 9.24 mmHg) was the only significant parameter when compared to that in Group B (22.96 ± 7.17 mmHg, P = 0.000003). TSC in Group A was significantly shorter than that in Group B (P = 0.00092), and %CSC (P = 0.00004) and %PinCSC (P = 0.00342) in Group B were significantly higher than those in Group A. No statistically significant difference in %NinOSC was found between Group A and Group B (P = 0.76060). Juxtacanalicular tissue (JCT) in Group A showed compact and weak staining with podoplanin, while the JCT and closed-SC area in Group B showed intense staining. In the Group A subjects, TSC (P = 0.04819) and OSC (P = 0.02867) were significantly shorter in the non-familial cases than in the familial cases. Platelet coagulations 10-37 μm in size at the defect of the SCE in the inner wall of the SC were observed in 8 eyes (18%) and 4 eyes (17%) in Group A and Group B, respectively. The platelets appeared to repair the SCE damage for maintaining the blood aqueous barrier in both groups of POAG eyes. Smaller SC diameters and accompanying TM abnormality were features observed in the young-onset JOAG patients, thus suggesting developmental abnormalities in the outflow routes. The collapse of SC lumen, presumably due to aging, was the feature observed in the elderly-onset POAG patients. In Group A, the significantly higher IOP, despite of no significant number of topical medications used prior to trabeculectomy, also suggested that JOAG eyes can be categorized as a distinct type of POAG from the eyes of elder-aged POAG patients. The SCE drop out observed in the glaucomatous eyes of the different age groups suggested that worsening of IOP control may possibly occur equally in both groups.

Keywords: Aging; Developmental abnormality; Glaucoma; Platelet coagulation.