In a recent survey by the American Society of Cataract and Refractive Surgery,¹ almost half of the organization’s members and meeting attendees did not perform minimally invasive glaucoma surgery (MIGS) procedures, and about one-quarter didn’t perform any laser procedures for glaucoma, even though selective laser trabeculoplasty (SLT) and MIGS stents are both excellent options that can reduce dependence on drops early in the course of glaucoma.

Visualization challenges are one reason that ophthalmologists avoid these procedures. The first challenge is simply a lack of familiarity with using a gonioscopic lens to visualize and treat the angle and key structures. Poor gonioscopic visualization can cause epithelial complications and missed shots (with accompanying inflammation) in SLT.

Even when surgeons are comfortable using a gonio lens, the tremendous amount of natural variation in the trabecular meshwork (TM) and iridocorneal angle anatomy can make it confusing to understand what they are seeing. For example, the TM can be heavily pigmented — or not pigmented at all. Bleeding may interfere with good visualization. It is surprisingly easy to mistakenly treat the wrong tissue or incorrectly place a MIGS device. Stents can be accidentally injected into the sclera or ciliary body, or they can be overimplanted deeply into the posterior wall, for example, rendering them ineffective or risking a complication. In one study, 72% of iStents (Glaukos) were not optimally positioned with the stent head within the canal.²

A patient recently presented to our practice who had undergone a goniotomy procedure elsewhere. The surgeon was off by one landmark on visualization (Figure 1) and instead of the intended goniotomy, accidentally opened up the ciliary body, causing cyclodialysis. There are several treatments in the development pipeline that have the potential to improve visualization or make it less critical for a successful glaucoma procedure.

Femtosecond Laser

ViaLase is developing the ViaLuxe laser system, which combines a femtosecond laser and integrated optical coherence tomography (OCT) (Figure 2) for a noninvasive glaucoma treatment called femtosecond laser image-guided high-precision trabeculotomy (FLigHT). This technology is unique from both an imaging and a treatment standpoint.

First, a gonioscopic patient interface stabilizes the eye and images it at the micron level, allowing for very precise location of the TM and Schlemm’s canal (Figure 3). Although OCT imaging of the angle can be accomplished with anterior-segment OCT, that technology is only practical in the clinic. The use of OCT in the surgical setting presents new opportunities for improved visualization. This has happened already in laser cataract surgery, where integrated OCT has provided surgeons with great insights into the anatomy of the lens and capsule.³

The FLigHT treatment uses a gonioscopic femtosecond laser to create a nonincisional laser trabeculotomy. When the precision of the laser is guided by OCT imaging, the treatment can be applied noninvasively to create channels in the vicinity of collector channels without collateral damage to adjacent tissues. The FLigHT treatment was developed by Tibor Juhasz, PhD, a scientist who was also instrumental in the development of the first femtosecond lasers for refractive and cataract surgery, the IntraLase and LenSx lasers (now Johnson & Johnson Vision and Alcon, respectively). The femtosecond laser added a level of precision and safety that revolutionized LASIK flap creation and brought enhanced reproducibility to several aspects of cataract surgery, so the opportunity to use a femtosecond laser to create customized drainage channels in glaucoma are promising for glaucoma treatment.

Combining these 2 proven, leading-edge technologies (OCT and femtosecond laser) in a noninvasive glaucoma treatment should prove to be a better experience for the patient. For example, FLigHT could be performed as a standalone procedure, rather than in the operating room or only at the time of cataract surgery.

Results from early studies of ViaLase’s technology have been positive.^4-6 In a 2-year pilot study, the ViaLase technology demonstrated a very good safety profile, and the investigators observed a reduction in intraocular pressure (IOP) with the procedure.⁶ Mean IOP reduction was 32% with no washout (Figure 4), with 82% of eyes achieving >20% reduction and 53% of eyes achieving >25% reduction in IOP. In all, 88% of eyes achieved IOP of ≤18 mmHg, with no adverse events. As ViaLase moves through the process of obtaining the CE Mark in Europe and FDA 510(k) clearance in the United States, additional data from larger studies will become available.

Direct Selective Laser Trabeculoplasty

Another interesting new technology, the Eagle system for direct SLT (Belkin Vision), would not only improve visualization but also eliminate the need for gonioscopy altogether (Figure 5). An automated, noncontact procedure, direct SLT is performed through the limbus, without gonioscopy. Because of this approach, it does not require the surgeon to identify all the anterior segment landmarks to deliver the treatment to the correct location. By eliminating this barrier, direct SLT should be able to improve efficiency while maintaining the same or better efficacy that is achievable with current SLT lasers.

Belkin’s initial proof-of-concept and human trials were very promising.^7,8 In the ongoing multicenter, controlled GLAUrious trial, patients were randomized to either conventional SLT or direct SLT with the Eagle system.⁹ Results for IOP reduction, change in medications, and complications over 12 months should be available soon.

Practice Makes Perfect

Until these new technologies become available, the gonio lens serves as the foundation of all other gonioscopy skills, so a great way for surgeons to improve their skills at gonioscopy is simply to use the gonio lens more frequently in clinic to visualize the angle. Simply noting whether the angle is wide open or narrow and how pigmented the TM is can facilitate decision making in glaucoma care.

Another helpful recommendation is for surgeons to use a gonio lens in the operating room, until it becomes comfortable to use in the nondominant hand. This practice does not need to be during a glaucoma surgery. At the end of a cataract surgery, simply use the gonio lens to observe the angle and practice identifying other relevant structures. Finally, start implanting stents in patients with glaucoma who are undergoing cataract surgery. Cataract surgery represents an excellent, one-time opportunity to bring down the pressure in that eye and potentially eliminate one or more topical medications for the patient.

To conclude, here are some pearls for practicing intraoperative gonioscopy. It is important to keep the eye well inflated with viscoelastic and refrain from exerting too much pressure on the cornea with the gonio lens. The incision and flow of fluid during intraocular surgery can already impede the surgeon’s view. Too much pressure on the cornea can exacerbate this by causing corneal folds or striae. You can also stain the TM with trypan blue to make it easier to locate. Finally, make your wounds carefully (more anteriorly) to avoid nicking surface blood vessels that will cause blood to pool on the surface of the eye, impeding the gonioscopic view.

Conclusion

Minimally invasive glaucoma surgery has already brought tremendous change to glaucoma care. The development of new technologies to overcome the visualization challenges of MIGS, SLT, and goniotomy will further advance our field and provide more options for surgeons and patients. GP

Nathan M. Radcliffe, MD, is a clinical assistant professor of ophthalmology at Mt. Sinai School of Medicine and an attending physician at New York Eye Surgery Associates in New York, New York. He reports consultancy to Lumenis, Belkin, ViaLase, Elios, Glaukos, Allergan, Alcon, New World Medical, and Sight Sciences. Reach him at drradcliffe@gmail.com.

References

1. 2019 ASCRS Clinical Survey 2019. EyeWorld. Accessed April 17, 2023. https://supplements.eyeworld.org/eyeworld-supplements/ascrs-clinical-survey-2019
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3. Waring GO 4th, Chang DH, Rocha KM, Gouvea L, Penatti R. Correlation of intraoperative optical coherence tomography of crystalline lens diameter, thickness, and volume with biometry and age. Am J Ophthalmol. 2021;225:147-156. doi:10.1016/j.ajo.2020.12.021
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6. Nagy ZZ, Kranitz K, Ahmed IK, et al. First-in-human study of femtosecond laser image guided high-precision trabeculotomy (FLigHT) for glaucoma treatment: 2-year outcomes. Presented at: American Society of Cataract and Refractive Surgery 2023 annual meeting.
7. Geffen N, Ofir S, Belkin A, et al. Transscleral selective laser trabeculoplasty without a gonioscopy lens. J Glaucoma. 2017;26(3):201-207. doi:10.1097/IJG.0000000000000464
8. Goldenfeld M, Belkin M, Dobkin-Bekman M, et al. Automated direct selective laser trabeculoplasty: first prospective clinical trial. Transl Vis Sci Technol. 2021;10(3):5. doi:10.1167/tvst.10.3.5
9. Congdon N, Azuara-Blanco A, Solberg Y, et al. Direct selective laser trabeculoplasty in open angle glaucoma study design: a multicentre, randomised, controlled, investigator-masked trial (GLAUrious). Br J Ophthalmol. 2023;107(1):62-65. doi:10.1136/bjophthalmol-2021-319379