To implement Coma, we will build upon the setup from Spherical Aberration. This time, as we want the effect to "trail away" towards the periphery, we will incorporate a Transform Node into the setup and again apply a subframe workflow to its 'scale' value. The Expression is: ((frame % 1)*scale_Increase)+1  - substitute scale_increase, which determines the amount of trail (for example, a small amount such as 0.05 might be sufficient).