Combining laser with minimally invasive glaucoma surgery to impact IOP

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.¹

I am primarily a cataract and refractive surgeon with a high-volume practice in Dothan, Alabama, United States. People travel from far away for cataract surgery and are usually referred by optometrists. When we do the cataract procedures, we also have this one chance to improve patients’ IOP.

When patients come in with early-to-moderate glaucoma, I combine laser with several minimally invasive glaucoma surgeries (MIGS). In over 90% of cases, I perform MicroPulse cyclophotocoagulation (CPC) as well as a canaloplasty and a trabecular meshwork (TM) bypass. In my experience, the effect of the combination is additive.

I 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 effective at lowering IOP than the TM bypass alone with cataract extraction.²

There are a lot of misconceptions about CPC treatments. Some think of CPC as an aggressive, end-stage procedure that can cause significant adverse effects 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. I 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 I am targeting a bigger reduction in IOP, I 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. I have found the process to be 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.^3,4 Instead, they create a stress response that induces a biological effect.⁴

In my opinion, 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.

I 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%.^5,6 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 deep-set 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 I perform the procedures, follow-up consultations are carried out by the patient’s referring doctor. Some of the referring doctors are located hours away from my practice. This makes it especially important for us to use procedures that will not cause pressure spikes or leave the patient’s eyes inflamed.

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.

After surgery, our clinic sends information to the referring doctor. For patients who have MIGS procedures, the postoperative follow-up schedule is generally no different from that for uncomplicated cataract procedures.

While patients are having cataract surgery, we are really doing them a service if we also address glaucoma, which is a long-term threat to their vision. I support being proactive and using all three procedures together. In my experience, this has been very safe and effective, and more than 60% of patients treated in this way are able to come off drops and reach target IOP.

Sebastian B. Heersink, MD

T: 001-800-467-1393

Dr Heersink is an ophthalmologist with Eye Center South in Dothan, Alabama, US. A graduate of the Massachusetts Institute of Technology, US, he received his medical degree from Georgetown University, Washington DC, US. He was a research fellow at the National Eye Institute, part of the National Institutes of Health in Bethesda, Maryland, US, and completed his ophthalmology training at Wills Eye Hospital in Philadelphia, Pennsylvania, US. Dr Heersink is a paid speaker for Iridex.

References

1. Heijl A, Leske MC, Bengtsson B, et al. Reduction of intraocular pressure and glaucoma progression: results from the Early Manifest Glaucoma Trial. Arch Ophthalmol. 2002;120(10):1268-1279.

2. Heersink M, Dovich JA. Ab interno canaloplasty combined with trabecular bypass stenting in eyes with primary open-angle glaucoma. Clin Ophthalmol. 2019;13:1533-1542.

3. Yu AK, Merrill KD, Truong SN, et al. The comparative histologic effects of subthreshold 532- and 810-nm diode micropulse laser on the retina. Invest Ophthalmol Vis Sci. 2013;54:2216-2224.

4. Inagaki K, Shuo T, Katakura K, et al. Sublethal photothermal stimulation with a micropulse laser induces heat shock protein expression in ARPE-19 cells. J Ophthalmol. 2015;2015:729792.

5. Zaarour K, Abdelmassih Y, Arej N, et al. Outcomes of micropulse transscleral cyclophotocoagulation in uncontrolled glaucoma patients. J Glaucoma. 2019;28:270-275.

6. Subramaniam K, Price MO, Feng MT, et al. Micropulse transscleral cyclophotocoagulation in keratoplasty eyes. Cornea. 2019;38:542-545.