The dancing eyes of coal miners and deuterium drinkers

I once took an overnight bus from Toronto to NYC. While certainly an inexpensive means of transport, it's crap having to disembark at the border and be shuffled through security just as you're settling in for the ride. Yet, if you're like me, the worst is still to come. I'm an eternal optimist when it comes to sleeping while travelling. Transatlantic flight? No problem, I'll just pack my inflatable neck pillow, pop a Benadryl, and snooze the time away. In practice, this of course doesn't work and I end up going ever so slightly mad with my own thoughts.

Anyway, so here I am on a long bus trip and I can't sleep. Towards the end, being exhausted and having spent much of the journey staring out the window, my eyes started to go a little loopy. The world began to blur and jump around a bit. I had developed oscillopsia. Fortunately, it went away after we arrived at the bus terminal, but I can still clearly remember the sensation.

One of the causes of oscillopsia is "dancing eyes", which involves your eyeballs striking out on their own and repeatedly moving rapidly in one direction and then more slowly back in the other direction. Nystagmus, as it's technically called, itself has many causes (e.g. neurological disorders, drugs, midway rides at the fair). It's essentially your inner ear getting tricked into telling your brain that your head is rotating when it's not. When your head actually rotates while you're staring at something, your brain makes your eyeballs move in the opposite direction so you can remain focused on whatever it is you're looking at. Always compensating, the brain is.

One of the stranger causes of involuntary eye flickering arose in the coal mines of the United Kingdom. Miners' nystagmus is suspected to be the result of spending long hours underground in poorly illuminated tunnels staring at black walls of coal. Interestingly, while it was one of the most common occupational illnesses in the UK during the early 20th century, it was practically unheard of in the United States. This was thought to be due to a combination of better lighting in US mines and an underlying contagious anxiety among UK coal miners about developing the condition, which in its worst form meant being unable to work. The nuances of miners' nystagmus and its origins are perhaps best left to Dr. Ronald S. Fishman, who wrote a thorough yet engaging article on it. I encourage you to give it a gander.

Nystagmus has also been reported among railway train dispatchers, hand compositors, crane workers, jewelers, and drafters. The commonality among these jobs is having to spend a lot of time looking closely (and often back and forth) at something, which appears to fuzz up the brain somehow. For example, a big part of being a railway train dispatcher, at least in the time before fancy electronic signalling systems, involved focusing intently on a huge sheet of graph paper used to keep track of train movements.

A sample of heavy water produced in Norway circa WWII (Source)

In addition to working certain jobs, eye oscillations can result from drinking non-water liquids. Having a couple of pints of lager can cause a phenomenon known as positional alcohol nystagmus, where tilting your head to the right causes your eyes to flicker quickly to the right (and then more slowly back to the left). However, if you drink about half a can of pop worth (~180 mL) of heavy water (deuterium oxide) or glycerol (mixed 1:1 with water, otherwise it's super goopy), the reverse effect will occur (i.e. tilting your head to the right will result in rapid eye flicks to the left).

This weirdness is explained by the buoyancy hypothesis. The idea is consuming liquids with densities different from water really screws with the semicircular canals of the inner ear, which enable the brain to sense the rotation of your head so it can compensate accordingly.

Inner workings of the inner ear

The canals consist of loops filled with liquid endolymph connected to bulb-like ampullae. Each ampulla contains a gel-like mass called a cupula. When the cupula moves, sensory cells (hair cells) contained within it transmit information to the brain. When you aren't drunk or dosed up with viscous liquids, the endolymph and cupula have the same density. This means they both only move if your head is rotated (i.e. undergoes angular acceleration), the movement then being conveyed to your brain as a "hey, the head is rotating" message.

However, when you ingest heavy water, glycerol, or alcohol, they enter your bloodstream via your gut and are carried throughout your body. Destinations include the capillaries at the base of the cupula. The liquids move into the cupula more rapidly than they do into the endolymph, so the cupula becomes relatively more or less dense. Consequently, it can be moved by gravity when you tilt your head to the side, duping your brain into thinking your head is rotating.

Due to their impact on the inner ear, ingesting alcohol, heavy water, or glycerol can can cause dizziness, nausea, and the incredibly uncomfortable sensation that the room is spinning. Interestingly, a study examining heavy water-induced nystagmus found the level of nausea experienced by subjects who drank heavy water was inversely related to how much booze they regularly consumed. A further study with cats found it was possible to cancel out the opposite nystagmus directions by administering a mixture of alcohol and heavy water! Presumably drinking other liquids will cause nystagmus, but there aren't many you can consume in large enough quantities to cause it without becoming very ill and risking death or permanent injury.


References

Fishman RS. 2006. Dark as a dungeon: The rise and fall of coal miners' nystagmus. Archives of Ophthalmology 124(11):1637-1644. [Full text]

McCord CP. 1931. Occupational nystagmus in train dispatchers. Journal of the American Medical Association 96(14):1131-1134.

Money KE, Myles WS. 1974. Heavy water nystagmus and effects of alcohol. Nature 247(5440):404-405.

Rietz R, Troia BW, Yonkers AJ, Norris TW. 1987. Glycerol-induced positional nystagmus in human beings. Otolaryngology-Head and Neck Surgery 97(3):282-287.

Smith HC, Riesenman FR. 1945. Unusual forms of nystagmus, with a review of the literature. Archives of Ophthalmology 33(1):13-15.