Preface for AES special series “recent glaucoma surgeries”

In recent years, surgical techniques for glaucoma have undergone significant changes. The only proven treatment for glaucoma with established evidence is the reduction of intraocular pressure (IOP). To achieve good control of the IOP, a stable and very small outflow, which is 1.2 to 2.9 µL/min in the healthy eye, must be maintained (1). Since Cairns’ landmark report in 1968, trabeculectomy has long been considered the gold standard for this purpose. The procedure creates a small drainage pathway that allows aqueous outflow into the subconjunctival space through a tiny gap between a scleral flap and scleral bed. However, surgical outcomes are largely influenced by wound healing, conjunctival condition, scleral flap design, suturing technique, and the use of anti-scarring agents, making trabeculectomy technically demanding and unpredictable (2). Reported postoperative early complications include shallow anterior chamber, hypotony maculopathy, or choroidal detachment, with postoperative visual loss in up to 43.9% of patients (3). Even when early complications are managed, patients remain at lifelong risk of bleb leaks and infections.

To address these problems, alternative surgical approaches such as tube shunts and canal opening surgeries have been developed. After a long history of unsuccessful attempts, the first clinically useful tube shunt device was the Molteno implant (4). Although its introduction was groundbreaking, the surgical outcomes of the Molteno implant had significant limitations, which prompted further refinement. These improvements diverged in two main directions.

The first pathway led to the so-called second-generation implants, consisting solely of a tube. Devices in this lineage include the Ex-PRESS, PreserFlo (InnFocus), and Xen, which utilize biocompatible materials, such as metal, styrene-block-isobutylene-block-styrene (SIBS), and porcine collagen-derived gelatin cross-linked with glutaraldehyde, respectively, to minimize tissue reaction. In addition, the reduced tube caliber was designed to provide safe and stable aqueous humor outflow, ensuring a controlled and constant flow. In this special series, Drs. Han and Ishida will discuss this.

The second pathway gave rise to the so-called third-generation implants, composed of a silicone tube connected to an aqueous reservoir (plate). In this design, aqueous humor is diverted outside the eye through the tube, stored over the plate, and subsequently absorbed through the surrounding capsule. Although the concept is straightforward, refinements in both surgical technique and biomaterials are essential to minimize surrounding tissue damage and reliable long-term outcomes (5). The Paul Glaucoma Implant, discussed in this special series, represents one such advancement developed through these continuous improvements. In this series, Drs. Muhammad, Narita, and Matsuda will discuss this topic.

Another approach to lowering IOP is to reduce the outflow resistance at the physiological drainage pathway, the Schlemm’s canal, a concept rooted in Barkan’s goniotomy (6) and Smith’s trabeculotomy (7). Because these procedures generally achieved a mild reduction in IOP, they were long criticized and failed to gain widespread adoption. However, with the development of Trabectome by Minckler, their effectiveness and safety attracted renewed attention. These procedures were subsequently reclassified under the category of minimally invasive glaucoma surgeries (MIGS) and have gained wide acceptance in recent years (8).

The trabeculotomy and gonioscopy-assisted transluminal trabeculotomy (GATT) described in this series by Drs. Khalil and Snchez highlight this important development. We hope that this special series will convey to readers the recent paradigm shifts in glaucoma surgery.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, Annals of Eye Science for the series “Recent Glaucoma Surgeries”. The article did not undergo external peer review.

Funding: None.

Conflicts of Interest: The author has completed the ICMJE uniform disclosure form (available at https://aes.amegroups.com/article/view/10.21037/aes-25-51/coif). The series “Recent Glaucoma Surgeries” was commissioned by the editorial office without any funding or sponsorship. E.C. served as an unpaid editorial board member of Annals of Eye Science from August 2024 to December 2026 and served as the unpaid Guest Editor of the series. The author has no other conflicts of interest to declare.

Ethical Statement: The author is accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

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5. Chihara E, Tanito M, Kono M, et al. Different patterns in the corneal endothelial cell loss after pars plana and pars limbal insertion of the Baerveldt glaucoma implant. Am J Ophthalmol 2023;253:12-21. [Crossref] [PubMed]
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8. Chihara E, Hamanaka T. Historical and Contemporary Debates in Schlemm's Canal-Based MIGS. J Clin Med 2024;13:4882. [Crossref] [PubMed]

Etsuo Chihara