sentences:  However, because SLT is performed using a much lower power laser, it does not appear to affect the structure of the trabecular meshwork (based on electron microscopy) to the same extent, so retreatment may be possible if the effects from the original treatment should begin wear off, although this has not been proven in clinical studies.ALT is repeatable to some extent with measurable results possible.An iridotomy involves making puncture-like openings through the iris without the removal of iris tissue.