I've experienced this any number of times, mostly when backpacking in the Adirondacks in overcast conditions. I've woken up in the middle of the night with no feeling of vision at all -- no sense of light or dark. It can be extremely disconcerting and similar to the feeling of drowning, for anyone who's also experienced that.
The article also suggests the phenomenon is temperature related, which I'd confirm. The times I've approached true panic for feeling "blind" have been between -20 and 30 degrees Fahrenheit, while I've always seen more of a mid to dark brown at warmer temperatures, from 50F up.
I'm pretty sure the temperature of the rhodopsin in your eye was above 30 degrees Fahrenheit :)
A toad's eye temperature can vary because it's cold-blooded. If humans' experience of eigengrau varies with outside temperature, well that's interesting and deserves study.
The article also suggests the phenomenon is temperature related, which I'd confirm. The times I've approached true panic for feeling "blind" have been between -20 and 30 degrees Fahrenheit, while I've always seen more of a mid to dark brown at warmer temperatures, from 50F up.