The effect of SLT on the aqueous humor dynamics is currently unknown. Given the lack of demonstrable thermal damage on histopathologic examination5, it is unlikely that the effects of SLT could be mechanically mediated. There has been some suggestion of a potential interaction of IOP lowering effect when prostaglandins and SLT are used together9,10. This suggests that there could be a possible sharing of mechanisms between SLT and prostaglandins. The IOP lowering effect of SLT may be mediated in part by effects on uveoscleral pathways in addition to the trabecular outflow pathway. This study will determine the changes in aqueous humor dynamics produced by SLT that lead to its IOP lowering effect. SLT is a Q switched frequency doubled Nd:YAG laser. The duration is 3 nanoseconds and spot size 500 microns. Power varies from 0.5-1.5 mJ and total number of spots can be between 50-over 100. The mechanism of action may be disruption of melanosomes, but this has not been unequivocally proven yet.