Dr. Karl and I chatted briefly over Twitter about this last night.

The word of the day is “Pupillometry.” Vampires can sprout fangs and talons, of course, but our pupils dilate far wider than the color of our irises, giving our eyes a black or dark red appearance when seen “vamped out” since the observed sclera (whites of the eye) almost disappear. As a supernatural predator, it’s one of the hardest things to conceal about ourselves in the wild since sudden widening is an involuntary response to danger and desire… even in mortal humans.

From Wikipedia: “Pupillometry is the measurement of pupil diameter in psychology. The method examines humans (including infants) and animals. Pupillary responses occur from birth and are involuntary. Pupil dilation of 0.5 mm can occur when elicited by psychological stimuli.” Like other parts of a lie detector test, the pupil diameter can provide an involuntary physical clue akin to a change in breathing or galvanic skin response.

Cool, huh? Fine: I’m a science nerd. Anyway…

The size of the human eye is slightly smaller than a full-size gumball, just 24 millimeters wide. The color iris portion is a about the width of an M&M (red ones were my favorite), averaging 12-15 millimeters wide. Like the aperture of a camera, the pupil in the center can expand to a maximum of 6-7 millimeters in diameter, so some color is always visible…if you’re human.

Fun fact: Vampires, have incredible visual acuity. On the standard 20/20 human scale, an eagle might have 20/4 vision while a hawk has 20/2 vision; they can spot crawling ants during a fly-over. Incredible, sure, but if the doctors at Cedarcrest Sanctum are correct, Vampires have a 20/1 visual acuity or better. Let me put that in perspective for you: I can’t just see a fingerprint on a mirror from across a 20-foot room; I can tell you who it belongs to if I’ve seen it before… and which fingertip.

Okay, end tangent; back to pupils. When light decreases, your iris opens the pupil to take in more light and improve your vision, just like a camera, and contracts again when more light is available. The problem is that this also happens involuntarily when something attracts your attention, whether aroused or fearful. Humans have a maximum aperture opening of 7mm… good but not great.

Vampires are essentially nocturnal predators; our irises open far wider — a stunning 16-18 millimeters or about 70% of an eyeball’s width — and are unfortunately more readily noticeable to the observant.

“My… what big eyes you have!” Uh oh: busted.

The good news is we can control this mostly involuntary response the same way you can: being aware of it and guarding our thoughts, which isn’t always easy (for us) when there’s fresh blood around. It’s when we’re lost in thought (read: daydreaming) and are being observed by sneaky humans that we have the greatest chance of getting caught.

We can always make you forget what you saw, of course, but that’s not entirely fair, is it? Hey… I never asked to be a walking lie detector with built-in reprogramming capability.

Keep each other safe.

~ Janiss

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