SLT & ALT are
equivalent in their capacity to decrease the IOP in glaucoma patients, which is
a surprising result in view of pronounced differences between both laser
instruments. Moreover, each laser produces different effects at the treatment
site, as only ALT induces mechanical alterations, due to collateral thermal
effects, while SLT induces no apparent tissue alterations, due to the lack of
such thermal effects. The lack of coagulative necrosis produced by SLT is
related to the nanosecond duration of each pulse and the selective targeting of
melanin chromophores. Such selectivity was demonstrated in vivo in TM tissues
especially prepared to contain non-pigmented TM cells & heavily pigmented
macrophages. The application of SLT obliterated macrophages leaving the
non-pigmented lining TM cells intact. Both SLT & ALT induced the synthesis
of IL-1 alpha, IL-1 beta, & TNF alpha as well as the recruitment of
macrophages. These common
biological responses may play a more decisive role in the mechanism of action
of both laser instruments to lower the IOP in glaucoma therapy than mechanical
alterations.