Following the leads offered by responses here, i have been reading about the scientific basis for the idea that the eyes are the windows or mirrors of our “souls. Here are my conclusions so far, if anyone is interested.
Most of the literature focusses on pupil dilatation. Here is a good summary on it.
Beyond adjustment to ligt intensity (it’s primary function), pupil size has been linked to a wide varieties of mental states: sexual arousal, fear, concentration, sleepiness, introversion, depression, etc. Sexual arousal has been the most studied but by far not the only factor at play.
E.g. pupil size increases in proportion to the difficulty of a task at hand. Calculate nine times 13 and your pupils will dilate slightly. Try 29 times 13 and they will widen further and remain dilated until you reach the answer or stop trying.
Pupil dilation can also betray an individual’s decision, concluded a 2010 study led by Wolfgang Einhäuser-Treyer, from Philipps University Marburg in Germany. Participants were told to press a button at any point during a 10-second interval, and their pupil sizes correlated with the timing of their decisions. Dilation began about one second before they pressed the button and peaked one to two seconds after.
Scientists don’t know why our eyes behave this way and there’s apparently no way to guess scientifically whether an individual’s pupil dilatation is due to sexual arousal, interest, concentration, fear, decision making, or any of the multiple mental events that have been linked to pupil dilatation in separate studies. Which does not mean that it’s undoable, only that we don’t know how to do it yet.
Oddly, pupil dilatation and constriction are controlled by two distinct nervous systems: the so-called “sympathetic system”, known for triggering “fight or flight” responses, induces pupil dilation, whereas the “parasympathetic system”, known for “rest and digest” functions, causes constriction. Both systems function unconsciously, meaning you can’t decide to open or close your pupils.
Finally, a 2007 study from a certain Matt Larsson from the Örebro university (Sweden) showed that personality traits such as aggressiveness or empathetic-ness correlate with the crypts and furrows of their iris. Iris crypts and furrows are “grooves” in the outer surface of the iris, one of the reasons why iris colors are striated, and apparently linked to the iris muscles that shrink or dilate the pupil.
They are visible upclose, as in Dutchess’ story on this thread, and fairly stable. They are used in biometric iris recognition for that reason. See this picture
The study is silent on whether emotional changes can be correlated with changes in color patterns in the iris, but i suppose that would make sense.