Evolving Microinvasive Glaucoma Surgeries

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Article initiated by:

Ana IM Miguel, Pauline Rault

All contributors:

Daniel B. Moore, MD, Ana IM Miguel

Assigned editor:

Qi N. Cui, MD PhD

Review:

Assigned status Update Pending

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Surgical Glaucoma Therapy

Preserflo

This drainage device, made from a bio-inert and highly compatible material called styrene-block-isobutylene-styrene or SIBS, measures 8.5mm with an outer diameter of 350 microns and 70 microns of internal diameter. Preserflo was formerly known as InnFocus MicroShunt. The implantation of these devices is performed ab externo and can be performed alone or in combination with cataract surgery. Concerning the surgical technique, the operative procedure consists first of all in the creation of a conjunctival flap of a size of about 4 to 6 mm starting from the lamina, followed by a peritomy with disinsertion of the conjunctiva and the Tenon. The exposed sclera must be thoroughly cleaned and left without residual tissue. Any bleeding should be cauterized. Applying mitomycin for 2 minutes, using small sponges, will decrease future scarring risk. The next step is to build an intrascleral tunnel whose starting point will be 3 mm from the limb and which will have to be 2 mm long by 1 mm wide. A perforation from this canal, passing through the iridocorneal angle and to the anterior chamber, is initiated using a 25 gauge needle to make the bed of the implant.

Finally, the micro-shunt is introduced through the previously formed tunnel, taking care to position its distal part towards the anterior chamber and its anterior part under the conjunctival-tenonian plane, as evidenced by the subconjunctival filtration bubble, a marker of the effectiveness of the technique. The future stability of this implant is ensured by the fin present within it. The flap will be closed by stitches in the limb.

Several studies have been carried out on this microshunt; Juan F Batlle et al. conclude a success rate of 100% at one year and 95% at three years concerning the desired criteria of IOP < or = 14mmHg and IOP reduction > or = 20%. The complications found in this prospective, non-randomized study involving 23 eyes were transient ocular hypotonia in 13% of cases and transient choroidal effusion in 8.7% of cases, all self-limiting . In 2023, a review of the literature conducted by Michaël Balas et al. found a better safety profile and a faster recovery time for MIGS compared to traditional glaucoma surgeries. However, this analysis also found a lesser degree of IOP reduction.

Finally, regarding the complications of this technique, a study conducted in 2022 by J. CLIN Med et al. found a rate of between 2.5 and 20% of hyphema, 1.0 to 7.4% corneal edema, 0.0 to 5.7% obstruction of the device and 5.9 to 150% need for filter bubble switching.

HYDRUS

The Hydrus microstent is an 8mm crescent-shaped implant made of nitinol, a flexible alloy of nickel and titanium. After the corneal incision, the implant is placed at the level of the scheme's canal using a pre-loaded manual injector system. Once installed, this open structure allows the dilation of the scheme canal by approximately 90°, thus performing an ab interno trabecular bypass to bypass the trabecular flow. This surgery can also be performed in combination with cataract surgery.

In a study realized in 2016, Steven Vold et al. found a superiority in the results of glaucoma treatment in terms of intraocular pressure and the need to resort to hypotonic medical treatment post-operatively when using combined cataract and microstent surgery Hydrus versus cataract surgery alone, two years before the operative management. In a recent study, Antonio M Fea et al. confirm that this device effectively reduces intraocular pressure and ocular drug treatment burden.

Some transient postoperative complications have been identified, such as corneal edema, hyphemia, anterior synechiae, poor positioning of the implant, obstruction of the device, or peak of intraocular pressure.

MIMS

The minimally invasive minisclerostomy procedure represents a recent surgical technique of ab externo filtration surgery without stenting, the principle of which is represented by a permanent sclerocorneal drainage canal. The operating procedure is performed using an activation system used to operate a handpiece associated with a 600 micron needle, which in turn has a 300 micron triangular blade that rotates around its longitudinal axis. The needle is inserted into the subconjunctival space and the blade is extended into the limbic area to create a drainage space at the sclerocorneal junction. Thus, a passage tunnel is created between the anterior chamber and the subconjunctival space. The main complication known to date of this procedure is obstruction of the incision site by the iris. The results of this procedure are encouraging, and studies are currently underway to further develop the results.

ELIOS

The ELIOS minimally invasive surgical technique represents a new technology within MIGS. It uses high-precision, non-thermal laser ablation to create ten microchannels in the trabecular mesh. The cold laser's advantage is that it minimizes tissue fibrosis and helps bypass the main area of resistance to aqueous flow.

This procedure aims to improve the flow of the aqueous humor within the Schlemm’s duct, preserving the anatomy of the iridocorneal angle as much as possible.

Studies carried out by ELIOS Vision found that the lowering of intraocular pressure was maintained at least eight years of age, and 80% of patients assessed were no longer required to continue drug treatment at one year post-operatively. Several other studies, including one randomized controlled trial, four prospective case series, and 5 retrospective studies, have shown a decrease in intraocular pressure between 20% and 40% compared to the figures initially presented by the patient and a decrease in drug treatment post-operatively.

In 2021, A. Moreno-Valladares et al. studied the efficacy of this surgery combined with cataract surgery. They highlighted a complete success at 12 months in terms of lowering intraocular pressure in 62% of eyes and 58% of eyes regarding the cessation of drug treatments. Minor and transient complications were reported for 5 out of 34 eyes studied, and 1 patient underwent filtration surgery.

Conclusion

Since their appearance in treating glaucoma about twenty years ago, MIGS have become a prominent part of glaucoma management. These techniques have the advantage of a lower risk of hypotonia and complications related to the filtering bleb, but also entirely satisfactory or even promising results regarding intraocular pressure reduction, the reduction of medical treatments for glaucoma post-operatively, and improvement in quality of life while maintaining visual function.