Disclosed is a method for preparing a prostaglandin derivative of formula :which comprises reacting an aldehyde represented by formula :with a 2-oxoalkyl phosphonate in a reaction solvent under the presence of alkali hydroxide as sole base. The link module also including a second serial interface. In a second step, the ROI is binarised into foreground and background voxels based on at least one threshold selected using anatomical knowledge. The thermoelectric generator contacts the heat dissipation fin and is electrically connected to the electric cooling module. Various dynamic control algorithms for such systems and other optical systems have been disclosed. The image processing unit obtains a plurality of reference objects from the eye image so as to recognize the eye movement direction and to confirm password input.