Pricks in your eyes, i.e. both vexatious and pernicious, for the eye is a tender part, and a wound there is very mischievous.
Related Commentaries of Numbers 33:55
Numbers 33:55
55 But if ye will not drive out the inhabitants of the land from before you; then it shall come to pass, that those which ye let remain of them shall be pricks in your eyes, and thorns in your sides, and shall vex you in the land wherein ye dwell.