SLT uses extremely short duration, low energy pulses of laser energy to selectively target pigmented cells in the drainage angle of the eye (the trabecular meshwork). The short duration of the laser pulses minimises collateral thermal damage to adjacent non-pigmented cells. Electron microscopy of the trabecular meshwork treated by SLT shows little mechanical disruption of the trabecular meshwork (5). It is thought that the treatment stimulates certain white blood cells called macrophages to release cytokines(chemical messangers) which increase the permeability of Schlemm’s canal. This allows fluid to escape from the eye more easily, lowers the eye pressure and protects the optic nerve.