Hi Aabid
Actually there are various parameters that are measured in Amplitude Units (AU),for example eye height it is defined as the 3σ distance between two neighboring eye levels and Eye Level is the amplitude level used to represent data bits, measured in Amplitude Units (AU). since it is amplitude it has to be measured in meters and hence the unit ‘m’. i am attaching a link that may prove helpful i hope.
Best Regards
Burhan
http://in.mathworks.com/help/comm/ref/commscope.eyediagram.html