For sub-nanosecond pulses incident on the retina, damage mechanisms arising from high pressure within the melanosome absorber become important. This paper investigates the formation of stress waves generated in tissue as a result of laser exposure. This will eventually lead to a determination of the manner in which thermomechanical waves cause damage in cellular material such as the retinal pigment epithelium. The first step in understanding how stress waves are generated within melanosomes requires determination of how energy `channels' into separate mechanisms. The present lack of an equation of state for the melanosome/cellular system limits our ability to determine how the absorbed energy is divided between thermal and mechanical processes. We will use the fundamental definition of the experimental Gruneisen parameter as an approach to get the necessary equation of state. This will lead to melanosome temperature and internal pressure at the end of an ultrashort pulse.