Article

Micropulse Trans-scleral Laser Therapy for Glaucoma

A potential noninvasive therapy for mild-to-moderate cases.

Micropulse trans-scleral laser therapy (MP-TLT) is an increasingly established modality for treating glaucoma. Effective at multiple disease stages, micropulse TLT delivers all the benefits of continuous-wave (CW) trans-scleral cyclophotocoagulation, but without as much thermal destruction; it is a safer course of treatment available to our glaucoma patients.1 The procedure is performed using the Iridex Cyclo G6 laser in its micropulse treatment mode with the MicroPulse P3 probe. Micropulse technology delivers a series of repetitive short “on” pulses followed by longer “off” periods to control temperature rise and prevent thermal buildup in the tissue and deliver a desired effect to targeted tissue.

Less Risk Equals More Indications

Micropulse-TLT has a low rate of complications across multiple trials.2-6 With low risk of inflammation, hypotony, and bulbar atrophy, MP-TLT opens up treatment possibilities for a wide range of indications across a broad spectrum of patients. A recent study4 demonstrated its efficacy and sustained intraocular pressure (IOP) reduction in patients with uncontrolled IOP, and my personal experience confirms this. I consider MP-TLT for my patients with uncontrolled IOP and visual acuity worse than 20/40. Every patient of mine undergoes optical coherence tomography (OCT) before and following MP-TLT, and to date, none of these cases have developed cystoid macular edema. The overall safety profile has prompted me to use MP-TLT across a wide variety of indications. I determine when to use MP-TLT on a case-by-case basis.

Patients with virtually every form of glaucoma may benefit from MP-TLT, although I exclude patients presenting with uveitic glaucoma and phakic patients with 20/20 vision due to the possibility of laser-induced inflammation. If I have a concern that a valve or other incisional therapies might not be effective, my tendency is to first perform MP-TLT, check the IOP response, and, if necessary, proceed with an incisional therapy. However, as I have expanded the indications of MP-TLT, I have seen a corresponding decrease in the performance of valve and other internal procedures.

Surgical Protocol and Settings

Preoperatively, I instruct patients to cease the use of prostaglandin analogs 3 days prior to the procedure due to its association with inflammation, and to continue aqueous suppressant medications, such as beta-blockers, carbonic anhydrase inhibitors, and alpha agonists until the day before laser treatment. At the end of the procedure, I instill 2 drops of 1% prednisolone and 1 drop of 1% atropine.

Probe movement and speed are important factors. To reduce limitations to movement, I perform the procedure under propofol in the operating room rather than with a retrobulbar block or lid speculum. My practice is to move the probe 180° (from 3 to 9 clock hours and vice versa) for 18 seconds each pass (Figure 1). In my experience, slow probe movement maximizes the laser effect. Additionally, I employ viscoelastic to facilitate probe movement and because of its ability to improve transmission of laser energy. Although it is not my practice, some surgeons will employ a subconjunctival injection of dexamethasone or similar steroid in an effort to minimize potential inflammation and to facilitate a seamless recovery from the laser procedure.

Figure 1. Micropulse trans-scleral laser therapy being performed with the Iridex Cyclo G6 laser.

Using a 2,000-mW energy setting and a 31.3% duty cycle, I will vary exposure time according to each patient’s needs. After several cases, I have found that the initial recommended setting of 80 seconds per hemisphere is sometimes not enough, so I usually start at a minimum of 90 seconds per hemisphere, and in some cases I use more than 100 seconds.

Postoperative Care

I prescribe 1% prednisolone every 4 hours and a nonsteroidal anti-inflammatory drug twice daily. At postsurgical day 1, I assess IOP and inflammation to elect whether or not to prescribe hypotensive medications. If necessary, I start patients on aqueous suppressants first and will add prostaglandins only as a last resort after a 3-week wait. This is due to the nature of prostaglandins to act on the blood–aqueous barrier and promote inflammation. The procedure truly is noninvasive. Patients leave the operating room without any physical limitations, and most are able to see soon after the procedure.

Helpful Tips for Treatment

Stay at least 1 mm behind the limbus to avoid the possible side effect of mydriasis. This practice may also prevent pupil dilation after laser treatment.

Utilize topical steroids and topical nonsteroidal anti-inflammatory drugs postoperatively for at least 3 to 4 weeks to decrease inflammation and to avoid cystoid macular edema. For patients with high IOP postoperatively, I reinstate the use of antiglaucoma medications until inflammation subsides, and then discontinue the steroid.

To Repeat or Not to Repeat

It is important to manage our patients’ expectations. Initially, MP-TLT is an unremarkable treatment and takes about 30 days to stabilize. I explain to my patients that this is a less aggressive treatment approach, and that approximately 30% of my patients require retreatment. If the patient has responded to the treatment but a greater effect is desired, I will recommend another application after 90 days. I do not repeat the procedure in patients who do not respond to MP-TLT initially; I recommend proceeding to incisional options for those patients.

Many patients will experience waning effects over time. This is not failure, and reapplication is our first course of action. With each application, we extend the time before patients must resort to more invasive options.

Early Intervention in the Treatment Paradigm

There is substantial experience with and evidence of the efficacy of treating eyes in the late disease stage of glaucoma. Multiple case studies have been presented indicating that patients can benefit from treatment in the early disease stages. Recently, a retrospective study of 61 eyes of patients with glaucoma and visual acuity better or equal to 20/60 was published by Varikuti et al. Among the 61 eyes, 46 had not undergone glaucoma incisional surgery.7 After 12 months of follow-up, mean IOP was reduced 40.2% from baseline, and the mean number of antiglaucoma medications was reduced by 0.82. The probability of complete success (IOP range 6-21 mmHg or ≥20% IOP reduction, BCVA loss ≤2 lines, no reoperation for glaucoma) ranged from 74% at 1 month to 75% at 12 months. Although mean BCVA did not change significantly, 10 eyes (16.2%) showed a reduction of visual acuity >2 Snellen lines following the procedure, 5 of them due to cataract.

This study was the first to report MP-TLT in only good-vision patients. The authors concluded that MP-TLT should be considered earlier in the management of glaucoma and can possibly be offered as an alternative to incisional glaucoma surgeries.

Conclusion

IOP reduction is highly dependent on the type of glaucoma treated. My own patient outcomes indicate that the most dramatic reduction of IOP is typically seen in cases of neovascular glaucoma, whereas regular pseudophakic, open-angle glaucoma cases usually see a 35% to 40% reduction in IOP. In my experience, MP-TLT has been a virtually risk-free intervention for patients with high IOP. GP

References

  1. Aquino MC, Barton K, Tan AM, et al. Micropulse versus continuous wave transscleral diode cyclophotocoagulation in refractory glaucoma: A randomized exploratory study. Clin Exp Ophthalmol. 2015;43(1):40-46.
  2. Gavris MM, Olteanu I, Kantor E, Mateescu R, Belicioiu R. IRIDEX MicroPulse P3: innovative cyclophotocoagulation. Rom J Ophthalmol. 2017:61(2):107-111.
  3. Barac R, Vuzitas M, Balta F. Choroidal thickness increase after micropulse transscleral cyclophotocoagulation. Rom J Ophthalmol. 2018;62(2):144-148.
  4. Zaarour K, Abdelmassih Y, Arej N, Cherfan G, Tomey KF, Khoueir Z. Outcomes of micropulse transscleral cyclophotocoagulation in uncontrolled glaucoma patients. J Glaucoma. 2019;28(3):270-275.
  5. Yelenskiy A, Gillette TB, Arosemena A, et al. Patient outcomes following micropulse transscleral cyclophotocoagulation: Intermediate-term results. J Glaucoma. 2018;27(10):920-925.
  6. Sanchez FG, Lerner F, Sampaolesi J, et al. Efficacy and safety of micropulse(r) transscleral cyclophotocoagulation in glaucoma. Arch Soc Esp Oftalmol. 2018;93(12):573-579.
  7. Varikuti VNV, Shah P, Rai O, et al. Outcomes of micropulse transscleral cyclophotocoagulation in eyes with good central vision. J Glaucoma. 2019;28(10):901-905.