Stress response has 2 main components:
Quick response, within minutes, is by the Sympathomedullary Pathway (SAM): hypothalamus > sympathetic nervous system > release of adrenaline and noradrenaline from the adrenal medulla > stimulation of the heart, dilation of the muscle arteries, constriction of the gut and skin arteries, glcogenolysis (the breakdown of ...
According to recent studies, drought stress does not consistently lead
to increases in the pH of xylem sap. One article which discusses
interspecies differences is Vit Gloser, et al., "The dynamics of
xylem sap pH under drought: a universal response in herbs?," Plant and
Soil 409, nos. 1-2 (2016): 259-272.
As to what may have prompted the textbook authors ...
Essentially, evapotranspiration is the sum of evaporation and plant transpiration from the Earth's land and ocean surface to the atmosphere.
Here are some links to articles about transpiration: https://biolympiads.com/plant-anatomy-and-physiology/
While cataracts is a possible explanation, the much more likely explanation is this answer about light adaptation.
There's a significant amount of literature about perceptional hue shifts with varying adaptation to brightness. While these experiments were not done with monocular variants, it's reasonable to believe that the effects measured can affect eyes ...