8 0 9 2 85 18 4 7919 0 75 0 6 0 15 7 78 17 0 72rapid gelling 5 1 80 0 14 8 4 8 95 19 7 90______________________________________ p polymer s solvent and ns nonsolvent this phenomenon has its limits and the shrinkage is only manifested up to a certain concentration of solute for example the gel dipped in 0 9 nacl solution physiological serum shows a shrinkage of 21 7 the same gel dipped in a 5 nacl solution has almost the same shrinkage of about 23 this is one of the fundamental properties of materials for use in corneal refractive surgery and particularly for intracorneal implants this permeability is an essential result for the maintenance of the corneal physiology on which the transparency of the cornea depends nutrient and metabolic flows the transport of dissolved gases oxygen and carbon dioxide water migration must not be hindered by the presence of the lens the implants according to the present invention show through their particular structure very good permeability the permeability to water to physiological serum and to various dissolved substances was measured by means of a test bench constituted by a tank provided with a stirrer the membrane tested was placed in sealed manner in contact with a 6 6 polyamide support hence it separates the tank into compartments that of the solution that of the filtrate all the measurements were carried out on samples of hydrogel of copolymer according to the invention containing 80 of h 2 o in the form of membranes of a thickness of 0.