When your vision is literally blocked by too much hair.

As amazing as it often is, biology can be equally messed-up up at times.
In Tennessee, U.S., a whitetail deer was found ambling around the streets with a condition that made it appear as if it had hair growing on its eyeballs. Yes, you read that right.
Called a corneal dermoid, the extremely rare condition is described as an abnormal flesh growth or a benign tumor on the deer’s cornea (the transparent part of the eye covering the iris and pupil) made of tissues usually found in other parts of the body in this case, skin tissue complete with hair follicles.
The condition has so far only been documented in just one other whitetail deer in the state, according to the Quality Whitetails magazine published by the National Deer Association.
A wildlife biologist told the magazine that he thought the deer “maybe could tell day from dark”, but “wouldn’t think it would be able to see where it was going”.
“I’d compare it to covering your eyes with a washcloth. You could tell day from night, but that’s about it.”
The hairy patches of skin were likely formed while the deer was still in the womb, according to Dr. Nicole Nemeth of the University of Georgia’s veterinary school, who also said that instead of a clear cornea being formed, the tissue instead formed skin with proper hair follicles, which grew into hairy patches as the deer aged.
It also happens to humans.
Curiously, dermoids have also been observed in humans, albeit in extremely rare instances. According to LiveScience, doctors may only see such cases about a couple of times in their entire careers.
Unlike the deer which had a dermoid covering the entire center of its cornea, dermoid cases in humans called limbal dermoids more often form at the intersection of the cornea and the sclera (the white part of the eye surrounding the iris).
Cases of limbal dermoids typically cause sufferers blurred vision, but not to the extent that they have serious problems with sight.
In one such case in 2013, a man had a limbal dermoid that similarly to the deer caused strands of hair to sprout from a small part of his eyeball. According to researchers, the growth had been present since birth, and grew in size until it was about 5 milimeters in diameter.
While limbal dermoids can be surgically removed for cosmetic reasons, they typically do not affect the patient’s eyesight.
If you found this medical condition oddly fascinating, you might want to read up on another recent hair-related medical incident here.
Read more science stories:
9 alternative uses for condoms. ‘Cause let’s face it, you’re not getting any.
Scientists have engineered spinach plants that know how to send emails
Endangered ferret is cloned from a long-dead ferret
Cover image sourced from National Deer Association and Live Science.