Similar thing happened to one of mine, took her to vets they removed the thorn but it had punctured the fluid at the back of the eye, vet said if left it would dry up, she cut a layer of skin from the lower eye lid and pulled it over the puncture and stitched it to the eye ball to try and seal the puncture, 4 weeks later the dogs back to normal with very slight scar tissue and no sign of sight loss, top job by the vet