Right before our eyes there's a dark hole in what we see. Not only don't we see some of what's right in front of our face, but we don't even notice the gap. Our illusion of a seamless visual world is so strong that scientists used to think that the spot where our optic nerve enters the back of each eye gave us our sharpest, clearest vision – not a place where we are utterly blind. Now we call this spot of profound blindness the punctum cecum (A fancy Latin phrase for blind spot. Impress your friends).

Why don't we notice it? Perhaps because the blind spots in our two eyes are in slightly different places, so our brain fills in the gap? This is partially true. But try this: quickly close one eye and look somewhere new. You won't see a gaping hole, even for an instant. What we see instead is something our minds make up, based on whatever data we have, ignoring the rest. We color-match and pattern-match the background with astonishing speed. If we're looking at a red polka dot pattern, there are still red dots wherever we would expect them to be. Try it. (Instructions). Map the size of your own blind spot.

The way our brains handle blind spots works brilliantly, most of the time. We're fooled, though, if what's near the center of our vision doesn't match the color or pattern we would expect -- which brings me to doctors and patients.

As physicians, we think we see patients very clearly. We're looking and listening and paying attention. But something else is also happening. With astonishing speed, our medically-trained brains begin to recognize and fill in patterns from a few bits of information. We often make a diagnosis within seconds of walking into a room, unconsciously eliminating data gaps from what we expect to see. Most of the time this works very well (I couldn't get through the day without it!). But sometimes, when what's happening doesn't match the most common patterns – and especially in the long tail of rare diseases – we draw startlingly wrong conclusions and miss what look like in retrospect to be obvious diagnoses.

I suggest two things:

Physicians – In every encounter, take at least a brief sideways look at the situation; notice something unique about this patient that doesn't fit a stereotype, even if it's something very small and seemingly irrelevant. Practice direct observation where the patient is the real center of vision, not the center of our pattern recognition. And always ask yourself, at least briefly, “What might I be missing? What if I'm wrong? In other words, map the size of your blind spot.

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