Yes, SLT can be repeated several times if required. Most patients just require 1 treatment. Treatment has been shown to be effective if repeated as soon as 6 months after the first treatment.

Source reference:
Gupta A & Jindra LF. “Selective Laser Trabeculoplasty as Repeat and Long-term Treatment in Glaucoma Patients.” Abstract 141 presented April 8, 2006.