What creates the sand in your eyes (usually found in the morning)? Why are there varying levels of sand?
First, welcome to the boards. Drop you coat off in the back bedroom and get something to eat. Chips and dip are in the living room, and there’s a cold keg on the back deck. Don’t forget to sign up for the darts tournament!
Now to the sand. Lots of stuff can get in your eyes during the day, from dust to solidifying proteins secreted by the eye itself (this is why you had to clean hard contact lenses every day). Blinking serves multiple purposes. It smooshes (yeah, it’s a scientific term) around the liquids to keep you eye moist, but it also pushes eye goop to the bottom of the eye, where it collects at the lower lid.
Incidentally, you blink from the outside of your eyes to the inside - even at night. While you sleep, you continue to blink, just not as you know it. Your eyelids twitch. This outside to inside blinking pushes the shmutz (another scientific term) toward the corner of your eye. It eventually dries to form the sand, or as y Grandmother called it, “sleep”.
different amounts are due to different amounts of stuff collected during the day.
And you thought the sandman was bringing you a dream… 
Se non e vero, e ben trovato
See an earlier thread: What is the medical term for “sleep crust”
Once, I asked this question of my optometrist. He said it was dead cells. I didn’t believe him and scooped up some of the still-damp sand from the corner of my eye and wiped it on a slide. Under a microscope, lo and behold! Cells! Turns out most of the sand is dead cells from your cornea, who have given their lives so you can see.
A sudden, substantial increase in sand is Not a Good Sign, and you should get checked by a professional, especially if you wear contact lenses.
Varying levels of sand may be due to cyclical changes in the cornea, but could also be the result of leaving more on your pillow and less on your eyes. Crying before you sleep may also wash out varying levels of cells.
Welcome to the boards. There’s lots of cool stuff in the archive.