Hi,
Generally, very deep acne scars that are less than the diameter of the punch (usually 3mm in diameter) are candidates for punch excision as these scars respond very poorly to other modalities of acne scar treatment such as subcision and fractional lasers. Such very deep acne scars with a small surface diameter are also known as “ice-pick” scars.
The punch excision converts the deep ice-pick scars to a superficial line scar which subsequent resurfacing procedures will help improve further.
Hope this helps!