(A) The OTP obtained with ASL in cortical (dotted lines) and nuclear (solid lines) lens lipid membranes of eye lenses from human donors of different age groups. Data for age groups 41–60 and 61–70 years are reproduced, respectively, from Reference 42, Copyright 2013, with permission from Elsevier, and from Reference 18, Copyright 2014, with permission from Springer Publishing. (B) The same data as in (A) but plotted as a function of the Chol/PL mixing ratio in the suspension of lens lipid membranes. Notice that above the Chol/PL mixing ratio of ~2, the Chol crystals are formed in liposome suspensions. Thus, the Chol/PL molar ratio in PCDs and the amount of Chol forming CBDs should not increase further. Chol crystals form presumably outside the membrane and can be detected by the DSC only after a significant amount of Chol is accumulated in these Chol structures. In our investigations, Chol crystals were detected only for nuclear membranes from the age group 61–70 years with the Chol/PL molar ratio of 4.4. For nuclear membranes from the age group 41–60 years with the Chol/PL molar ratio of 2.1 we were unable to detect Chol crystals.