The present invention relates to an ophthalmic solution comprising (i) bimatoprost or its pharmaceutically acceptable salt in an amount ranging from about 0.005% to 0.015% weight by volume; (ii) a biguanide compound in an amount ranging from about 0.003% to 0.05% weight by volume; (iii) an acylated amino acid in an amount ranging from about 0.01% to 0.1% weight by volume; (iv) pharmaceutically acceptable excipients and (v) purified water.