PROBLEM TO BE SOLVED: To provide a monomer for an eye lens which is high in transparency even if copolymerized with a hydrophilic monomer such as N-vinyl pyrrolidone, high in oxygen transparency, and also high in water wettability, and a polymer for an eye lens.SOLUTION: The monomer is expressed by a formula (a). [In the formula (a), X denotes a group selected from a N-Y and O. Y denotes an alkoxycal carbonyl ethyl group, an N-alkylamido ethyl group or the like. Rdenotes a group selected from H and a methyl group. Rdenotes a substituent selected from a 3-[tris(trimethylsiloxy)silyl]propyl group, a 3-[bis(trimethylsiloxy)methyl silyl]propyl group, a 3-[(trimethylsiloxy)dimethyl silyl]propyl group, a tris(trimethylsiloxy)silyl methyl group, a bis(trimethylsiloxy)methyl silyl methyl group and a trimethylsiloxy dimethyl silyl methyl group. n denotes an integer of 0 or 1].
