Fig. 18. Removal of trabecular block and peripheral iridectomy. A. Before removing the block, preplace four 10-0 nylon scleral flap sutures. With a Kelly or Crozafon-DeLaage punch, remove a block of trabecular tissue. B. With the scleral flap retracted over the cornea, place the punch at the anterior extent of the tunnel and excise tissue as needed to create the sclerostomy. C. The punch is used two to three times in order to remove an adequate block of tissue. Do not excise tissue posterior to the scleral spur or ciliary body bleeding occurs. D. A peripheral iridectomy ensures that the iris will not block the opening of the trabeculectomy. A peripheral iridectomy may be unnecessary in select cases.