Disclosed are photochromic contact lenses which include transparent organic materials having an index of refraction of more than 1.55. The material is prepared by radical polymerization of a polymerizable composition which includes (a) 80-95 wt % of at least one monomer represented by the general formula (I): where R is H or CH3 and m and n are independently 1 or 2; (b) 5-20 wt % of at least one aromatic monovinyl monomer; (c) an effective amount of at least one dye that imparts photochromic properties to the materials, selected from the groups of spiroxazines, spiropyrans and chromenes; (d) an effective quantity of a chain transfer agent; and (e) an effective quantity of a radical polymerization initiator. The chain transfer agent is a linear alkanethiol, and the radical polymerization initiator is a diazo compound.