The treatment of glaucoma is directed toward lowering IOP in order to prevent or slow progressive damage to the optic nerve. Surgery is indicated when medical therapy and laser treatment do not adequately reduce the IOP.1 Lasers also have a useful place in the management of elevated or decreased pressure during the postoperative period, and surgeons have developed various techniques for decreasing IOP and treating complications.

LASER SUTURE LYSIS

Trabeculectomy is the most commonly performed surgery for glaucoma. Ophthalmologists have transitioned from full-thickness sclerectomies to “protected” scleral flaps using a tight closure technique. The aim is to prevent hypotony and its associated problems such as poor vision, macular edema, shallow anterior chambers, and cataract formation.2 One of the most frequently employed techniques for postoperative IOP control is a partial release of the flap by laser suture lysis (LSL), which is often performed a few days to a few weeks after surgery. In LSL, the surgeon uses an argon or diode laser to cut sutures without disrupting the conjunctiva. A special lens (Blumenthal or Hoskins) provides him or her with a clear view of the suture under the conjunctiva (Figure). The parameters for treatment depend on the thickness of the bleb and the type of laser that is used. Usually, an application of laser energy at a low power setting (50-100 μm at 300 mW) suffices. A helpful hint is that scleral flap sutures should be tight and at least 4 mm long in order to make visibility and cutting easier.

The timing of LSL depends on whether antimetabolites were used during trabeculectomy. Although adjunctive mitomycin C (MMC) and 5-fluorouracil (5-FU) have improved the procedure's outcomes in terms of IOP control, their use has also increased the incidence of postoperative ocular hypotony and its associated complications.2 In our experience, in cases of trabeculectomy with adjunctive MMC or 5-FU, LSL should be avoided if at all possible during the first 5 postoperative days to prevent severe swings in IOP, the rapid onset of severe hypotony, and a shallow anterior chamber. In this situation, antiglaucoma medication usually controls the IOP for that interim. When 5-FU has been employed, LSL can be performed up to 2 to 3 weeks after surgery. If MMC was used, LSL can occur at a much later date. In 1993, Pappa et al showed that LSL can be effective even 21 weeks after trabeculectomy when intraoperative MMC was used. After LSL, digital pressure on the front of the eye may be used to elevate the bleb by forcing aqueous through the sclerectomy.3 Although there are many techniques for applying digital pressure, we instruct the patient to close the operative eye and look directly forward. Pressure is then applied through the eyelid to the front of the eye for up to 10 seconds in a slow, steady fashion. The IOP should be checked multiple times during this process to allow titration of the amount of digital pressure necessary to elevate the bleb and lower IOP without flattening the anterior chamber.

GONIOPUNCTURE OR SYNECHIOLYSIS

After trabeculectomy, the sclerostomy site may become occluded by the iris or a membrane. If the physician observes this complication with gonioscopy, he or she may wish to perform laser synechiolysis. The goal is to remove any overlying tissue that is obstructing the outflow of aqueous humor. Surgeons have successfully used both Nd:YAG lasers and the argon laser to clear the obstruction.4 The Nd:YAG laser may be aimed at the top of the synechiae and set on multiple pulses in order to create a vibration or incision that causes the iris to fall away. The surgeon can incise a membrane directly using powers similar to those for a laser iridotomy. Alternatively, using a goniolens, the surgeon can select a large spot size with an argon laser and apply a slow burn to pull the iris away from the sclerostomy site by shrinking it.

Laser treatment can also address problems after canaloplasty. If postoperative outflow is insufficient, the surgeon can perform goniopuncture with an Nd:YAG laser to create a direct pathway for fluid flow from the anterior chamber to the scleral lake.5,6

HYALOID DISRUPTION FOR MALIGNANT GLAUCOMA

Malignant glaucoma is among the most challenging problems ophthalmologists face. This sight-threatening form of angle-closure glaucoma misdirects aqueous humor into the vitreous cavity. Malignant glaucoma is characterized by flattening of the anterior chamber in the presence of a patent iridectomy and the absence of a suprachoroidal hemorrhage or fluid.7,8 In this situation, the IOP is usually elevated. Using an Nd:YAG laser, the surgeon performs a capsulotomy if the patient is pseudophakic and disruption of the anterior hyaloid in an attempt to create a passageway through which the aqueous humor can flow forward into the anterior chamber instead of being trapped in the vitreous. 9 Additionally, the administration of a cycloplegic such as atropine and steroids may help alleviate the problem. When medical and laser therapy fail, a vitrectomy (or lensectomy-vitrectomy) will correct the problem.10

EXTERNAL DIODE LASER OR ENDOPHOTOCOAGULATION OF THE CILIARY BODY

When the IOP is not controlled after multiple surgeries and maximum medical treatment is unsuccessful, diode laser cyclophotocoagulation can be useful. The surgeon applies diode laser energy transsclerally 1.5 mm behind the limbus to reduce the function of the ciliary processes, thereby decreasing the amount of aqueous produced and lowering the IOP. After a retrobulbar or peribulbar block, the eye receives 24 spots via an application of long duration (2,000 milliseconds) approximately 1.5 mm behind the limbus at a power just below that required to hear a “pop” (1,750 mW).11 The power required for treatment will vary considerably based on scleral thickness and the surgeon's level of experience. Transscleral cyclophotocoagulation may need to be repeated multiple times and may leave the eye inflamed. A loss of visual acuity is common after laser cyclodestruction, generally due to cystoid macular edema. This procedure should therefore be limited to patients with a visual acuity of less than 20/40. Noncontact transscleral Nd:YAG laser cyclodestruction also delivered through the sclera has been reported to be effective in refractory glaucoma as well.8

Endophotocoagulation (ECP) is another option for treating elevated IOP by destroying part of the ciliary body. ECP appears to be especially effective when combined with phacoemulsification and the implantation of an IOL. An 18- or 20-gauge probe (Endo Optiks) delivers endothelial photocoagulation for up to 300º of the ciliary processes through a single incision.12 Success corresponds to treatment of both the anterior and posterior portions of the ciliary body. The procedure causes whitening of the tissue and shrinkage of the ciliary processes but does not harm the core of the ciliary body. This internal approach causes less inflammation and postoperative pain than sclera-based diode cyclodestructive procedures, which destroy much more of the ciliary body.

LASER TREATMENT OF BLEBS

Overfiltering blebs are another complication of filtering surgery, particularly when adjunctive antimetabolites are used. In addition to hypotony, especially large blebs and those that allow aqueous humor to flow into the nasal or temporal subconjunctival space are prone to causing the symptoms of chronic foreign body sensation and epiphora.13 Addressing these problems entails reducing the size of the bleb or decreasing filtration through it. Options include surgically removing part of the bleb, placing compression sutures through the bleb, injecting autologous blood into the bleb, applying cryotherapy or chemical irritants (silver nitrate), or remodeling the bleb with an Nd:YAG or argon laser. Bettin et al used an Nd:YAG laser to induce bleeding in an overfiltering bleb by targeting blood vessels adjacent to the scleral flap.14 Another approach to shrinking the bleb is to paint it with a photoabsorbent dye and then apply laser energy (argon, krypton, holmium YAG, or Nd:YAG).15 This is done to enhance laser absorption. Laser energy is then applied to the surface to cause the bleb to shrink.

CONCLUSION

The proper application of laser techniques readily resolves many complications of glaucoma surgery. Moreover, using a laser enables the surgeon to address the issue in the office, thus avoiding inconvenient and expensive return trips to the OR.

Pedro Cervantes, MD, is an instructor of clinical ophthalmology at the Northwestern University Feinberg School of Medicine in Chicago. He acknowledged no financial interest in the product or company mentioned herein. Dr. Cervantes may be reached at pedrocf@hotmail.com.

Jon Ruderman, MD, is an associate professor of clinical ophthalmology at the Northwestern University Feinberg School of Medicine in Chicago. He acknowledged no financial interest in the product or company mentioned herein. Dr. Ruderman may be reached at j-ruderman@northwestern.edu.

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