Abstract: The invention relates to photochromic transparent organic materials presenting an index of refraction of more than 1.55, which are free of optical distortions and are prepared by radical polymerization of a polymerizable composition comprising:a) 80-95 wt % of at least one monomer represented by the general formula (I): ##STR1## where R=H or CH.sub.3, and m and n are independently 1 or 2; b) 5-20 wt % of at least one aromatic monovinyl monomer represented by the general formula (II): ##STR2## c) an effective quantity of at least one dye that imparts photochromic properties to the material, selected from the groups of spiroxazines, spiropyrans and chromenes;d) an effective quantity of a chain transfer agent; ande) an effective quantity of a radical polymerization initiator, characterized in that the chain transfer agent is a linear alkanethiol and the radical polymerization initiator is a diazo compound.