Odd circles on touch screen

My screen has acquired a couple of small circles near the edge of the screen, about 7mm in diameter. They appear to sit in between the LED display and the soft touchscreen surface. Looking from the side they appear to be about 0.5mm in depth - it looks like a circular crack in glass. I did wonder whether it was a coffee spill by Persons Unknown(!) but the marks are fixed, no sign of it being fluid - not moving.

Picture below is highly magnified - actual mark is just irritating, not a disaster.

Dell Inspiron 15 3537