Over the past 15 years, minimally invasive glaucoma surgery (MIGS) procedures have transformed the surgical management of glaucoma, making it safer and simpler. Most MIGS devices enhance the conventional outflow system by reducing resistance to outflow at the level of trabecular meshwork (TM) and the inner wall of Schlemm’s canal (SC). These MIGS devices either bypass the diseased proximal system through implantation of trabecular stents or open the TM/SC to varying degrees by ablating, excising, or tearing tissue.

Laser technology has been used in many different modalities (argon, diode, and YAG, among others) to treat glaucoma. The excimer laser, first used in 1987 for photorefractive keratectomy, has also been investigated as a glaucoma treatment. The excimer laser uses a combination of a reactive gas and an inert gas to electrically excite and emit energetic pulses of ultraviolet light. Unlike “hot” lasers that thermodynamically cut or coagulate tissue, the excimer induces an ablative effect, removing tissue with extraordinary precision by disrupting chemical bonds within the area of treatment without affecting adjacent tissue.¹ Also, excimer laser energy is minimally absorbed in water, thus providing unique benefits for intraocular surgery.²

The Excimer Laser Trabeculostomy Procedure

Considerations for the use of an excimer laser to treat glaucoma have evolved since the first treatment attempts in the 1980s. The initial approach sought to create an ab interno full-thickness scleral fistula, resulting in formation of a conjunctival bleb. As the delivery system and probe have become more sophisticated, the approach has also evolved. An excimer laser trabeculostomy (ELT) device that was developed by Elios Vision uses a specialized excimer laser device to create microchannels through the TM into SC.³

The Elios ELT device ablates portions of the TM by employing 308-nm laser energy that is transmitted through a fiberoptic probe (The 193-nm excimer laser wavelength commonly used for refractive procedures cannot be transmitted in this manner).^4,5 The resulting effect is the creation of trabeculostomy openings of 210 μm diameter, which reduce outflow resistance in the TM and SC, the major sources of resistance in the natural outflow system.⁴

Excimer laser trabeculostomy can be performed as a standalone procedure or in conjunction with cataract surgery. The probe, which is calibrated just prior to use, enters the anterior chamber through a clear corneal incision of at least 0.8 mm and is advanced across the anterior chamber under gonioscopic visualization until it is in contact with the TM. The laser energy is applied by depressing a foot pedal. The area of treatment is propagated over 3 clock hours of the angle by creating 10 microchannels approximately 1 probe-tip diameter (500 μm) apart. As the microchannels are created and the laser is delivered, the surgeon will see microbubbles arise around the probe, and slight blood reflux may be noted from the microchannels. Finally, the probe is removed from the eye and viscoelastic is irrigated.

It is worth noting the ways that the excimer laser is differentiated from other lasers used for the treatment of glaucoma, specifically selective laser trabeculoplasty (SLT), as their mechanism of action, characteristics of the laser, and laser effect on the tissue are remarkably different. Selective laser trabeculoplasty is based on the principle of selective photothermolysis, which refers to a confined thermal radiation of pigmented cells within a tissue.⁶ It utilizes a Q-switched, frequency-doubled, 532 nm Nd:YAG laser that selectively targets the pigmented cells of the TM with minimal collateral damage to neighboring cells. The mechanism by which SLT reduces IOP is unclear.^3,6 The thermal effect caused by SLT induces physical tissue alterations and elicits an inflammatory response, which leads to remodeling/scarring of the TM. This is most likely the reason that the IOP-lowering effect diminishes over a period of months to years.⁷

By contrast, the excimer laser is a “cold” laser that causes minimal thermal damage, has low tissue penetrance, and is nonlethal to neighboring cells,^1,4 thus minimizing the healing response and contributing to a long-term IOP-lowering effect.⁷ Selective laser trabeculoplasty alterations to the outflow system occur on a microscopic level, whereas the effects of ELT are more on the macroscopic level, being visible during and after treatment. These macroscopic microchannels may allow for a continued and long-term reduction in outflow resistance.

Safety and Effectiveness

Excimer laser trabeculostomy has been successfully performed in Europe since the late 1990s. The ExTra Laser System (MLase; later acquired by ELT Sight) device received CE marking in 2014. Thousands of European patients have been treated with these devices and other legacy systems (including, for example, the ExTra Laser System and the Aida laser from TUI-Laser), and multiple publications have reported on the performance and safety of the treatment, including several publications that have reported long-term outcomes (Table 1).

In May 2022, Reisen et al published a retrospective study of 128 patients (161 eyes) with glaucoma or ocular hypertension and cataract who underwent the combined phacoemulsification plus excimer laser trabeculostomy (phaco-ELT). Long-term success was defined as IOP ≥5 mmHg and ≤21 mmHg with the same or fewer postoperative medications compared to baseline, no loss of light perception vision, and no required subsequent glaucoma surgery within the follow-up period. The researchers reported long-term success rates of 81.3% at 1 year, 60.7% at 4 years, and 50.2% at 8 years, with 35% of patients reported as medication free at 4 years and only 3.6% requiring additional invasive filtering surgery during the 8-year follow-up period.⁸ The researchers reported an intraoperative complication rate of 8.7%, with posterior capsular rupture being the most frequent complication and postoperative complications typical of those seen after a phacoemulsification procedure. These results make the ELT procedure one of the MIGS procedures with the longest follow-up published to date.

In the United States, the Excimer Laser Trabeculostomy Glaucoma Treatment Study (ELTGTS) is currently ongoing under an investigational device exemption from the US Food and Drug Administration. This prospective, multicenter clinical trial is intended to evaluate the safety and effectiveness of ELT to reduce IOP in 318 patients with primary open-angle glaucoma undergoing cataract surgery.⁹

Conclusion

The ELT procedure offers an exciting advance in MIGS. Safe and effective IOP lowering and medication reduction without dependence on an external bleb and without a retained intraocular device promises to be a very useful option for treating glaucoma. GP

Mark J. Gallardo, MD, is a glaucoma specialist with El Paso Eye Surgeons in El Paso, Texas. Dr. Gallardo reports consultancy, speaker’s fees, and clinical trials with Glaukos, Alcon, and Ellex; clinical trials with Elios Vision, Sight Sciences, New World Medical, and Ivantis; and speaker’s fees from Aerie Pharmaceuticals and Bausch + Lomb.

Richard Lewis, MD, is a glaucoma specialist and cofounder of Sacramento Eye Consultants in Sacramento, California. He reports consultancy to Alcon, Aqua Health, Avellino, Avisi Technologies, AVS, Elios Vision, Iantrek, IOTA, MicroOptx, Orasis, Sanoculis, Thea, and Vialase. Reach him at rlewismd1@gmail.com.

References

1. Pidro A, Biscevic A, Pjano MA, Mravicic I, Bejdic N, Bohac M. Excimer lasers in refractive surgery. Acta Inform Med. 2019;27(4):278-283. doi:10.5455/aim.2019.27.278-283
2. Puliafito CA, Steinert RF, Deutsch TF, Hillenkamp F, Dehm EJ, Adler CM. Excimer laser ablation of the cornea and lens. Experimental studies. Ophthalmology. 1985;92(6):741-748. doi:10.1016/s0161-6420(85)33962-3
3. Nguyen A, Simon B, Doan R, et al. Advances in excimer laser trabeculostomy within the landscape of minimally invasive glaucoma surgery. J Clin Med. 2022;11(12):3492. doi:10.3390/jcm11123492
4. Durr GM, Töteberg-Harms M, Lewis R, Fea A, Marolo P, Ahmed IIK. Current review of excimer laser trabeculostomy. Eye Vis (Lond). 2020;7:24. doi:10.1186/s40662-020-00190-7
5. Funk J, Berlin MS, Ahmed II, et al. A new minimally invasive surgical procedure for the treatment of open-angle glaucoma: ELT. Paper presented at: The ASCRS/ASOA Symposium on Cataract, IOL, and Refractive Surgery; May 2, 2004; San Diego, CA.
6. McAlinden, C. Selective laser trabeculoplasty (SLT) vs other treatment modalities for glaucoma: systematic review. Eye. 2014;28:249-258. doi:https://doi.org/10.1038/eye.2013.267
7. Töteberg-Harms M, Hanson JV, Funk J. Cataract surgery combined with excimer laser trabeculotomy to lower intraocular pressure: effectiveness dependent on preoperative IOP. BMC Ophthalmol. 2013;13:24. doi:10.1186/1471-2415-13-24
8. Riesen M, Funk J, Töteberg-Harms M. Long-term treatment success and safety of combined phacoemulsification plus excimer laser trabeculostomy: an 8-year follow-up study. Graefes Arch Clin Exp Ophthalmol. 2022;260(5):1611-1621. doi:10.1007/s00417-021-05510-8.
9. A prospective, multicenter clinical trial designed to evaluate the safety and effectiveness of the ELIOS system to reduce intraocular pressure in patients with primary open-angle glaucoma undergoing cataract surgery. ClinicalTrials.gov identifier: NCT04899063. Updated September 29, 2022. Accessed October 7, 2022. https://clinicaltrials.gov/ct2/show/NCT04899063