Why are human eyes incredibly sensitive to nearly every stimuli but our eyelids can glide over them with no irritation?
In: Biology
It’s the same reason we don’t find the smell of oxygen to be totally nauseating – it’d make perfect sense, but animals with that trait wouldn’t last long, so we’ve adapted it out.
The inside of your eyelid is smooth, lubricated, and flexible. Eyes that can’t tolerate even that little irritation wouldn’t be very good at their job.
Most of it has to do with the oil produced by our meibomian glands located at the edge of each lid. The average human has between 60-80 of these little glands, and they’re actually what keep the eye lubricated, not tears.
Optometrist here. The inside of your eyelid is called the palpebral conjunctiva. They eye produces tears and this lubricates these surfaces. Dry eye can be caused by a variety of factors and if your eye is dry enough your lids do not glide as you describe. Giant papillary conjunctivitis, recurrent corneal erosion and Sjogren’s syndrome are big problems that cause huge discomfort.
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