The present invention discloses to a high refractive index polysiloxane (co)polymer comprising refractive index modifying groups chemically bonded in clustered configuration to the polysiloxane backbone. The invention also discloses methods for the preparation of such high refractive index polysiloxane (co)polymers. A polysiloxane according to the invention is very suitable for use as a material for the production of intra-ocular lenses.