An abrasion resistant coating composition for an optical element, wherein the composition is capable of forming an abrasion resistant coating on an optical element after ionic polymerisation, the composition comprising: a polymerisable epoxy monomer having an average of at least two epoxy groups in the monomer molecule selected from the group consisting of ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6 hexane diol diglycidyl ether, glycerine diglycidyl ether, pentaerythritol diglycidyl ether, bisphenol-A diglycidyl ether (BPADGE), bisphenol-F diglycidyl ether, and their extended chain analogs, 1,4-butanediol diglycidyl ether, diglycidyl ethers of tetrabromo-bisphenol-A, epoxy based ethers of 4,4'-biphenylene, trimethylol propane triglycidyl ether, pentaerythritol triglycidyl ether, glycerol triglycidyl ether, diglycerol triglycidyl ether, diglycerol tetraglycidyl ether, pentaerythritol tetraglycidyl ether, dipentaerythritol tetraglycidyl ether, tetramethylene glycol diglycidyl ether, 1,6-hexamethylene glycol diglycidyl ether, neopenthyl glycol diglycidyl ether, alicyclic hydrogenated bisphenol A diglycidyl ether, hydrogenated diglycidyl isophthalic acid ester, 3,4-epoxy cyclohexyl methyl-3,4-epoxy cyclohexane carboxylate, bis(3,4-epoxy cyclohexyl)adipate; diglycidyl hydantoin, diglycidyl oxyalkyl hydantoin; aromatic bisphenol A diglycidyl ether, bisphenol A diglycidyl ether initial condensate, diphenylmethane diglycidyl ether, diglycidyl terephthalic acid ester, diglycidyl isophthalic acid ester, diglycidyl aniline, triglycidyl isocyanurate, triglycidyl cyanurate, triglycidyl hydantoin; aromatic triglycidyl para- or meta-aminophenol, tetraglycidyl benzyl ethane, sorbitol tetraglycidyl ether, tetraglycidyl diaminophenyl methane, tetraglycidyl bisaminomethyl cyclohexane, phenol novolac epoxy resin, and cresol novolac epoxy resin; a (meth)acrylate monomer, the (meth)acrylate monomer having an average of at least three polymerisable double bonds in the molecule; a hardness enhancer, which is a colloidal metal oxide; and a cationic photoinitiator. a polymerisable epoxy monomer having an average of at least two epoxy groups in the monomer molecule selected from the group consisting of ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6 hexane diol diglycidyl ether, glycerine diglycidyl ether, pentaerythritol diglycidyl ether, bisphenol-A diglycidyl ether (BPADGE), bisphenol-F diglycidyl ether, and their extended chain analogs, 1,4-butanediol diglycidyl ether, diglycidyl ethers of tetrabromo-bisphenol-A, epoxy based ethers of 4,4'-biphenylene, trimethylol propane triglycidyl ether, pentaerythritol triglycidyl ether, glycerol triglycidyl ether, diglycerol triglycidyl ether, diglycerol tetraglycidyl ether, pentaerythritol tetraglycidyl ether, dipentaerythritol tetraglycidyl ether, tetramethylene glycol diglycidyl ether, 1,6-hexamethylene glycol diglycidyl ether, neopenthyl glycol diglycidyl ether, alicyclic hydrogenated bisphenol A diglycidyl ether, hydrogenated diglycidyl isophthalic acid ester, 3,4-epoxy cyclohexyl methyl-3,4-epoxy cyclohexane carboxylate, bis(3,4-epoxy cyclohexyl)adipate; diglycidyl hydantoin, diglycidyl oxyalkyl hydantoin; aromatic bisphenol A diglycidyl ether, bisphenol A diglycidyl ether initial condensate, diphenylmethane diglycidyl ether, diglycidyl terephthalic acid ester, diglycidyl isophthalic acid ester, diglycidyl aniline, triglycidyl isocyanurate, triglycidyl cyanurate, triglycidyl hydantoin; aromatic triglycidyl para- or meta-aminophenol, tetraglycidyl benzyl ethane, sorbitol tetraglycidyl ether, tetraglycidyl diaminophenyl methane, tetraglycidyl bisaminomethyl cyclohexane, phenol novolac epoxy resin, and cresol novolac epoxy resin; a (meth)acrylate monomer, the (meth)acrylate monomer having an average of at least three polymerisable double bonds in the molecule; a hardness enhancer, which is a colloidal metal oxide; and a cationic photoinitiator.