The invention relates to a passive sensing means (100) for a contact lens of a physiological parameter monitoring system, for detecting variations of a physiological parameter, in particular intraocular pressure, the passive sensing means (100) forming a resonant circuit comprising an inductor (101) and at least one capacitor (121, 122, 123, 124, 125, 126). The inductor (101) and said at least one capacitor (121, 122, 123, 124, 125, 126) are coplanar in only one layer. The invention also relates to a corresponding physiological parameter monitoring system.