P1 receptor can be divided into four subtypes of adenosine A1, A2A, A2B, and A3, while P2X receptors include subtypes of P2X1-7, and eight subtypes of P2Y receptors: P2Y1, P2Y2, P2Y4, P2Y6, and P2Y11-14, of which the A1, A2A, A3, P2X4, P2X7, P2Y1, P2Y2 and P2Y4 receptors play important regulatory roles in the inflammatory response in dry eye (6). Here, P2RY6 is linked to Keratoconjunctivitis sicca.