The invention relates to treatment apparatus (10) for correcting a refractive error of an eye (12) comprising:- a laser device (14) for separating corneal tissue by means of laser radiation (16)；- a control device (18) designed to control the laser device (14) to emit the laser radiation (16) for cutting out and/or ablating a volume (24) out of the surface (26) of the cornea (22) of the eye (12) in dependency on a measured pachymetry and/or topography of the cornea (22) and the refractive error of the eye (12), whereby the cut-out and/or ablated volume (24) in the surface (20) of the cornea (22) results in a shape of a closed ring, a partial ring, a crescent or a crescent shaped closed ring.Furthermore the invention relates to a method for controlling such a treatment apparatus (10), and to a protective mask (40) for an eye (12).
