Head mounted displays (HMD) are in widespread use for virtual environment applications and they are the focus of many discussions in ergonomics. Most of the HMDs coming onto the market without any proven ergonomic aspects - and this in times of pan-European regulations for display working places. Many tests have been done in the field of ergonomic aspects of HMDs, therefore, we saw this as an opportunity to delve deeper into the possibilities these display devices give us. This paper introduces technical aspects of head mounted displays and pertinent health concerns. It will help to show the possible ways of testing the ergonomic quality of these devices and permit comparisons to be made.