The lens (lens cristalina) is part of the light conducting and light refracting system of the eye. Transparency and light refraction are the main properties of the lens. Nutrients are supplied to the lens through the capsule by diffusion and active transport. The energy needs of the avascular epithelial structure are 10–20 lower compared to that of other organs and tissues. Such needs are satisfied through anaerobic glycolysis. Currently, there is insufficient information about the fundamental chemical mechanism underlying the existence of the lens in the healthy body, the mechanisms of its functional “survival” against the background of somatic disorder, such as diabetes. The paper reports the authors’ view of certain chemical aspects clarifying pathochemical alterations of the lens with the possible mechanisms underlying its “adaptation”/”protection” associated with the systemic disorder at the molecular level. In particular, the view of the involvement of glucose-6-phosphate dehydrogenase/ transketolase, the enzymes of the oxidative and non-oxidative phases of the pentose phosphate pathway belonging to the native crystalline fraction protein family, in the mechanisms underlying protection of the lens against the oxidative and osmotic stress, involvement of aldo-keto reductases in pathochemical alterations of the lens, as well as the role the NO, NO₃-, B₆, PQQ small molecules having an antioxidant cytoprotective effect is reported.