More factoid diggings about that neutral eye thing.
Awake, alert subjects do not seem to have a neutral eye position as the eyes are constantly fusing binocular images, fixating on objects at different distances while undergoing constant saccadic movements. *BTW, you are blind during those saccadic movements, otherwise vision would be a continuous blur.
There is an actual neutral eye position, occurring in the Physiological Rest Position and the Anatomical Rest Position, and its not very flattering. This position occurs during deep sleep, general anesthesia or death (prior to rigor mortis). Anatomical (at death) and physiological rest positions both involve some degree or total absence of eye muscle innervation. The eyes, under both conditions, are diverged (opposed to crossed) and rotated upward (more pronounced in death). You can also see this in blind people as well.
Another interesting and overlooked nuance is the fact that the pupil is not positioned in the center of the iris, as it seems to always be
depicted in 3d realistic human character work. You can look at an iris/pupil and immediately tell which eye it is and whether the head is right-side up or not, without seeing any other part of the eye. The pupil is always (statistically) located off-center, slightly toward the nose and slightly upward. If you see someone with a centered pupil, you are seeing an anomaly, or you are looking at an android! :surprised
Its a subtle nuance, but if beating the Uncanny Valley is to be achieved, all anatomical subtleties should be taken into serious consideration. :shrug:
And relating directly to the offset pupil is the fact that when gazing (fixating) on a distant object, lets say the moon, the eyes are diverged, not parallel. This is due to the fact that the visual axis (line from fixation object to fovea) is not in line with the optical axis, which is the line passing through the centers of the two lenses (cornea and crystalline lens). The visual axis is rotated outward (temporally) from the optical axis by about 5° and down about 1°, ending at the location of the fovea, that tiny pit located on the retina where all of our sharp vision takes place (within about a 2° cone of view). The visual axes of both eyes are parallel when looking at, say a star, moon or mountain peak. This diverges the optic axes and therefore the eyeballs. If the eye were a perfect optical system, the fovea would lay on the optical axis, in line with the lenses. I read somewhere that if the fovea were on the optic axis, visual acuity would be 2.5 times greater (less aberration to deal with). The pupil compensates for the odd fovea position (only partially) by being offset toward the nose and upward. The pupil has its own axis called the Pupillary Axis.
–Thought someone might be interested, beside me.
**I am not an ophthalmologist, so do your own fact checking.