Method for determining the inversion state of a soft contact lens

Method for determining the inversion state of a soft contact lens (CL) which is arranged in an interior space (10) of an inspection cuvette (1) and which is immersed in a liquid (L) contained in the interior space (10) of the inspection cuvette (1), the inspection cuvette (1) being pivotally arranged about a pivot axis (PA) for being positioned either in an inspection position in which the soft contact lens (CL) is inspected, or in a handling position in which the soft contact lens (CL) can be inserted into and removed from the interior space (10) of the inspection cuvette (1), the inspection cuvette (1) comprising:

• - a bottom glass (14) forming a lower boundary of the interior space (10), the bottom glass (14) having a concave inner surface (140) for the soft contact lens (CL) to rest on, the concave inner surface (140) facing towards the interior space (10);
• - a flat top viewing glass (13) forming an upper boundary of the interior space (10), the flat top viewing glass (13) being arranged such that an optical axis (OA) running normal to the flat top viewing glass (13) runs through the center of the concave inner surface (140) of the bottom glass (14);
• - a handling channel (11) which is connected at a first end thereof with the interior space (10), and at a second end thereof comprises a handling opening (12) for insertion of the soft contact lens (CL) into and removal of the soft contact lens (CL) from the interior space (10) through the handling opening (12) and the handling channel (11);
• the method comprising the steps of:
• - positioning the inspection cuvette (1) in the handling position;
• - through the viewing glass (13) obtaining (60) a dark-field image (4,5,7,9) of the soft contact lens (CL) arranged in the interior space (10) along the optical axis (OA);
• - identifying (61) a lens edge (LE) of the soft contact lens (CL) in the dark-field image (4,5,7,9);
• - determining (62) one or more characteristic values representative of the brightness of at least a portion of the lens edge (LE) in the dark-field image (4, 5, 7, 9);
• - comparing (63) at least one of the one or more characteristic values with a corresponding predetermined threshold value;
• and - determining (64) that the soft contact lens (CL) is inverted in case the at least one of the one or more characteristic values is equal to or above the corresponding predetermined threshold value;
• or - determining (65) that the soft contact lens (CL) is not inverted in case the at least one of the one or more characteristic values is below the corresponding predetermined threshold value.