Age-related levels of sclera collagen crosslinking have been studied in 75 patients aged 50-91 (averagely 69.9 ± 9.2 years) with various degrees of primary open angle glaucoma (POAG), whose sclera samples were obtained during deep nonpenetrating sclerectomy. The patients were divided into three age groups: 50-59 years (21 patients), 60-69 years (22 patients), and over 70 years (32 patients). 19 eyes of these patients had POAG stage I, 24 eyes had POAG stage II, and 32 eyes had stage III. To assess the level of collagen cross-linkage, sclera thermograms obtained by differential scanning calorimetry (Phoenix®, DSC 204, Netzsch, Germany) involving collagen denaturation temperature (Tm) and enthalpy value (∆Hm) measurements were analyzed. The level of collagen cross-linkage of glaucomatous sclera was found to increase with age and the stage of glaucomatous damage. However, the formation of excessive cross links associated with glaucomatous damage seems to play a more important role in damaging its structural and biomechanical properties than crosslinking of collagen complexes caused by natural aging, since the differences in values of thermomechanical parameters Tm and ∆Hm across different age groups (staying, respectively, within 0.8-1.0 оС and 0.3-2.1 J/g of dry residue) proved to be less substantial than the differences associated with the progression of glaucoma (varying, respectively, within 1.9-2.6 оС and 6.7-13.2 J/g of dry residue). The identified structural and biomechanical changes of the corneoscleral eye shell in patients with POAG do not fit into the pattern of natural aging processes; they are most probably based on the metabolic disorder of the connective tissue // Russian Ophthalmological Journal, 2016; 1: 19-26.