Trace elements composition of the scleral shell of the eye in various forms of glaucoma

Abstract

   Purpose:  a comparative study of the elemental composition of scleral biopsy specimens from patients with various clinical forms of glaucoma.   Material and methods.  44 patients aged 79.5 ± 2.5 were divided into three groups depending on the form of glaucoma: 16 patients with primary open-angle glaucoma (POAG) (group 1); 13 patients with normal tension glaucoma (NTG) (group 2); 15 patients with pseudoexfoliative glaucoma (PEG) (group 3). For elemental analysis, we used scleral biopsies obtained during planned surgical treatment of glaucoma (non-penetrating sinus trabeculectomy). Scleral fragments of 14 donor eyes with no history of glaucoma served as controls. The concentration of macroelements K, Mg, Ca, and Fe was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES, Agilent ICP-AES 720 ES, USA), while microelement concentration (Zn, Cu, Al, Mn) was measured using inductively coupled plasma mass spectrometry (ICP-MS, Bruker ICP-M S 820, Germany).   Results.  In all forms of glaucoma, scleral samples showed a varying increase in the content of such elements as Zn, Fe, Mg, AL, Ca, K. The highest content of Zn and Fe was found in the scleral tissue of patients with NTG, the difference with the control (p = 0.0001 andp = 0.0003) and with POAG (p = 0.0002, p = 0.0001) being highly significant. The difference between the content of Zn in scleral biopsies of patients with POAG and PEG was also statistically significant (p = 0.0002), whilst no significant difference in Fe content in the sclera (p = 0.69) was found between POAG and PEG Higher Mg concentrations as compared to the control were found in NTG (p = 0.00014) and POAG (p = 0.00002).Patients with POAG (p = 0.0005) and PEG (p = 0.00022) showed the highest accumulation of Ca in the sclera. No differences were found in Mg content of scleral biopsies between patients with NTG and POAG (p = 1.0), while the level of Ca in POAG (p = 0.02) and PEG (p = 0.00001) was significantly higher than in NTG. A significantly lower content of Cu was found in the sclera samples of patients with NTG (p = 0.022), POAG (p = 0.004) and PEG (p = 0.00004) as compared to the control, as well as a reduced content of Mn in POAG (p = 0.00003) and PEG (p = 0.0012). Contrarywise, NTG patients showed an increased content of Mn (p = 0.000003). No differences were found in the Cu content between the sclera of patients with NTG and POAG (p = 0.47), while Cu level in PEG was significantly lower than in POAG (p = 0.034) and NTG (p = 0.013).   Conclusion.  The macro- and microelement imbalance of the sclera of the eyes with different forms of glaucoma indicates differences in their pathogenesis. This can be the reason for the different severity of disorders of collagen biosynthesis and the formation of cross-links in the connective tissue structures of the sclera, as well as the varying degree changes in the hydrodynamics of the intraocular fluid, which on the whole can affect the level of intraocular pressure and the pattern of glaucoma development.