Patients became stratified into 4 study groups: A—visually impaired with T1DM and impaired dexterity; B—visually impaired with T2DM and impaired dexterity; C—visually impaired with T1DM or T2DM; D—patients without any impairment with T1DM or T2DM. Participants were asked to perform some test injections (dosing 10, 30, and 50 U) and complete a standardized questionnaire assessing the handling of the pen device. The procedure was repeated with a second insulin injector. In the end, patients evaluated the study by completing a comparative questionnaire. Here, INS is linked to type 1 diabetes mellitus.