In Light of Combining Laser-Based Treatment with MIGS to Reduce IOP Levels

In Light of Combining Laser-Based Treatment with MIGS to Reduce IOP Levels

February 14, 2022

New  minimally  invasive  surgical  modalities  have  shown  considerable  potential  in  intraocular  pressure (IOP)  and  the  number  of  post-surgical  medications  with  rare  complications. 

The  rising  popularity  of  these  devices and  procedures  may  represent  a  shift  in  treatment  paradigm  from  medical  therapy  towards  earlier  surgical intervention, especially in the treatment of mild-to-moderate glaucoma.

Selective laser trabeculoplasty (SLT) is as effective as medication in controlling IOP, which is why many physicians have adopted it as a first-line treatment to manage glaucoma without the compliance problems associated with medications.

SLT is also a valuable adjunct to microinvasive glaucoma surgeries (MIGS) in reducing IOP enough to reduce or eliminate medications.

Like MIGS, SLT is a step in the treatment paradigm between medications. MIGS and SLT are natural partners in reducing IOP without the risk of traditional glaucoma surgeries, such as trabeculectomy or tube shunts, or the compliance issues of medications.

When we are already discussing MIGS surgery for glaucoma, possibly in addition to cataract surgery, the idea of augmenting the IOP-lowering effects of those surgeries with a laser treatment makes sense to patients as well.

Elevated intraocular pressure (IOP) is the most significant risk factor for developing glaucoma and the only known risk factor that is currently treatable. In patients who already have glaucoma, reducing IOP slows the progression of the disease.

When patients come in with early-to-moderate glaucoma, surgeons combine laser with several minimally invasive glaucoma surgeries (MIGS).

In over 90% of cases, they perform MicroPulse cyclophotocoagulation (CPC) as well as a canaloplasty and a trabecular meshwork (TM) bypass. The effect of the combination is additive. Surgeons use either iStent (Glaukos) or Hydrus (Ivantis) to allow aqueous fluid to bypass the TM and flow out.

The canaloplasty, using the Omni Surgical System (Sight Sciences), dilates Schlemm‘s canal and the collector channels to enhance the natural outflow system.

The combination of TM bypass stents and canaloplasty with cataract extraction has been shown to be more eff ective at lowering IOP than the TM bypass alone with cataract extraction.

There are a lot of misconceptions about CPC treatments. Some think of CPC as an aggressive, end-stage procedure that can cause signifi cant adverse eff ects and inflammation. A decade ago, CPC was seen as a last resort.

Now that you do not have to use as much power, the procedure creates much less inflammation and the effect appears to be quite robust.

                                                                                                                            

Surgeons have not had issues with hypotony, and inflammation has only been an issue in very limited cases, such as a patient with uveitic glaucoma, and these cases were able to be controlled with topical steroids.

In more advanced glaucoma cases, when surgeons are targeting a bigger reduction in IOP, they use the Cyclo G6 Laser with the continuous wave G-Probe delivery device (both Iridex).

The continuous wave laser energy is absorbed by melanin in the ciliary processes, and coagulative necrosis of the ciliary body reduces aqueous production.

The process is effective and repeatable, but it involves tissue ablation and there can be more                    inflammation than with the MicroPulse CPC.

Transscleral Laser

More commonly, for mild-to-moderate glaucoma, I use the MicroPulse P3 delivery device with the Cyclo G6 Laser to perform transscleral laser therapy (TLT). MicroPulse technology divides the laser beam into microsecond bursts that are interspersed with longer resting intervals.

This allows the tissue to cool between pulses and reduces thermal build-up within the tissue targeted by the laser. These lasers do not cause thermal necrosis. Instead, they create a stress response that induces a biological effect.

MicroPulse TLT is an under-utilised non-incisional treatment, although its use is increasing. Iridex reports that 180,000 patients have been treated with its TLT in 80 countries.

Surgeons have started using the procedure more often and earlier in the overall IOP reduction process. MicroPulse TLT is 60–80% successful at lowering IOP by at least 20%.

As a surgeon, I have increased my power setting from 2,000 mW to 2,500 mW and slowed the speed of the three sweeps I do across each hemisphere to deliver more power to the tissues. This is a manufacturer recommendation, and I find it to be more effective.

Using the recommended 31.3% duty cycle, I now treat each hemisphere for 60–80 seconds by doing three sweeps of 20–25 seconds each. I avoid about 30 degrees at the 3 o’clock and 9 o’clock positions because there are long ciliary nerves there.

I am now using the revised MicroPulse P3 Probe. It is a little thinner and it is easier to position, especially in patients with deepset eyes. It has two plastic pieces—which look a little like bunny ears—that are placed on the limbus and help with alignment. It is very straightforward and quick.

I prefer to operate in an ambulatory surgery centre, and I do the CPC laser in the preoperative area, after the patient has received a peribulbar block, while the operating theatre is being prepared. This has created a very efficient flow for us.

Post-Surgical Approach

After the cataract extraction and the other MIGS treatments, the postoperative procedure is identical to my usual cataract postoperative regimen, which is generally an intracameral corticosteroid and antibiotic and a non-steroidal anti-inflammatory drop for 1 month.

Slightly fewer than 5% of patients develop cystoid macular oedema (CMO). This includes all patients, even those with epiretinal membrane and diabetes, so the rate of CMO does not seem to be any different from that for the standard cataract populations in my hands.

There is a less than a 10% risk of postoperative hyphaema with canaloplasty and trabecular bypass shunts. One tip when using shunts and stents is to leave the pressure somewhat higher at the end of surgery; this will reduce reflux into the anterior chamber.

Now that I do this, targeting a maximum pressure of 25 mm Hg, my hyphaema rate is probably between 2% and 4%. After we perform the procedures, follow-up consultations are carried out by the patient’s referring doctor.

Together with sending back patients who have quiet, unproblematic eyes, successful co-management requires communication and education. Before the procedure, the referring doctor should know that you perform CPC laser and MIGS procedures.

The doctor can then begin preparing the patient, both through discussions and by initiating medication for patients with mild-to-moderate glaucoma, as insurance companies require that patients be on medication before they have a trabecular bypass stent procedure.