Two glaucoma stents show modest two-year results in highly myopic eyes

A large retrospective study of highly myopic eyes has found that two widely used trabecular bypass devices for minimally invasive glaucoma surgery, the iStent inject and the Hydrus microstent, deliver modest pressure-lowering effects with low complication rates over two years, but neither device reached the minimal clinically important difference proposed for these procedures when combined with cataract surgery. The findings, published in Eye and Vision, offer the first dedicated look at how these implants perform in eyes whose extreme length and altered anatomy have long been suspected of complicating glaucoma surgery.

The research, a retrospective observational multicenter cohort study, drew on surgeries performed between January 2019 and December 2023 at three tertiary ophthalmology centers: Mahatma Eye Hospital in Trichy, India; Sydney Eye Surgeons in Australia; and the Singapore National Eye Center. The investigators enrolled 252 eyes of 207 subjects, of whom 128 eyes received the iStent inject and 124 received the Hydrus microstent. To qualify, eyes needed a refractive spherical equivalent of at least minus 6 dioptres before cataract surgery, an axial length of 26 millimeters or more, and a diagnosis of ocular hypertension or mild-to-moderate primary open-angle glaucoma, defined as a visual field mean deviation better than minus 12 decibels. Eyes with pre-existing ocular inflammation, anterior segment dysgenesis, or peripheral anterior synechiae were excluded, and every participant had at least twelve months of follow-up.

The two devices work in fundamentally similar ways. Trabecular bypass procedures enhance the eye’s natural aqueous outflow through the drainage angle, in contrast to traditional incisional operations such as trabeculectomy and tube shunt surgery, which create new drainage pathways but carry higher complication rates. The iStent series and the Hydrus microstent are indicated for mild-to-moderate primary open-angle glaucoma and have also shown good outcomes in ocular hypertension. Because many of these procedures use an ab-interno approach that minimizes collateral tissue trauma, they have been rapidly adopted as safer alternatives that still provide at least modest intraocular pressure reduction.

Highly myopic eyes, however, present a distinctive anatomical challenge. Myopia is a well-known risk factor for primary open-angle glaucoma, and studies have shown that eyes with moderate-to-high myopia of minus 3.0 dioptres or greater and an intraocular pressure of 20 mmHg or more are almost three times more likely to have the disease than non-myopic eyes. Structural changes in highly myopic eyes, including greater lamina cribrosa deformity at the optic nerve head and weaker scleral support, are thought to predispose the nerve to glaucomatous damage. Anatomical differences may also raise complication risks during surgery: cases of iStent inject malpositioning and over-implantation have been reported in highly myopic eyes, possibly attributable to scleral thinning, localized ectasia, and inadequate intraoperative visualization. Fixed-curvature canal-based devices such as the Hydrus may not fit the larger Schlemm’s canal diameter found in these eyes, and increased corneal striae during gonioscopy, reflecting decreased corneal hysteresis, can hinder device implantation.

Against this background, the study team tracked intraocular pressure, anti-glaucoma medication use, and visual acuity at one, six, twelve, and twenty-four months after surgery, and recorded complications including hyphema, peripheral anterior synechiae, and significant pressure elevation, the latter defined as a pressure of 30 mmHg or more or an increase of at least 6 mmHg from preoperative levels. At the twenty-four-month mark, 35.8 percent of Hydrus eyes and 30.0 percent of iStent eyes achieved a pressure reduction of at least 20 percent from baseline while remaining on anti-glaucoma medications. Without medications, the corresponding figures were 13.4 percent for Hydrus and 6.67 percent for iStent. Drop-freedom was achieved by 48.7 percent of Hydrus eyes and 38.5 percent of iStent eyes. An intraocular pressure of 15 mmHg or less with medications was reached by 55.2 percent of Hydrus eyes and 63.3 percent of iStent eyes, and without medications by 28.4 percent and 21.7 percent respectively.

The survival analysis painted a sobering picture of durability. The twelve-month cumulative risk of failing to maintain a pressure reduction of at least 20 percent with medications was 86.7 percent in the Hydrus group and 90.3 percent in the iStent group; without medications, the risks were 90.1 percent and 92.5 percent. Surgical success judged by American Academy of Ophthalmology guidelines was attained by 60.5 percent of Hydrus eyes and 53.8 percent of iStent eyes at two years, a difference that was not statistically significant. Both figures fell short of the 65 percent minimal clinically important difference threshold that the Academy’s Glaucoma Preferred Practice Pattern Committee proposed for minimally invasive glaucoma surgery combined with cataract surgery. Notably, those thresholds were benchmarked against published success rates of trabeculectomies and tube shunt surgeries, which range from 82.7 to 96.1 percent at one year but carry higher complication rates, and against standalone cataract surgeries, which achieved 46 to 61.9 percent at two years.

Safety results were encouraging. Significant intraocular pressure elevation was the most common complication, affecting 4.84 percent of Hydrus eyes and 4.54 percent of iStent eyes at one month, followed by hyphema, which occurred in 0.8 percent of Hydrus eyes and 4.5 percent of iStent eyes at the same timepoint. Rates of peripheral anterior synechiae formation were similar between groups, and no complications other than significant pressure elevations were noted at twenty-four months. Only three iStent eyes required further pressure-lowering procedures, one filtration surgery at one month, one deep sclerectomy at twelve months, and one selective laser trabeculoplasty at twenty-four months, while no Hydrus eye required any additional procedure. In the iStent group, one patient experienced a significant best-corrected visual acuity worsening of at least 0.2 logMAR, whereas no Hydrus eye did, although visual acuity was overall significantly better in the iStent group from six months onward. The authors noted that complication rates were so low, at five or fewer events per complication, that the study may have been underpowered to compare them reliably between groups.

Statistically, the two devices performed equivalently. The Hydrus microstent tended to outperform the iStent in the early postoperative months, achieving significantly greater proportions of eyes with a 20 percent pressure reduction without drops at one and six months, while the iStent tended to fare better later; by twenty-four months the groups no longer differed on any success criterion. Mean anti-glaucoma medication counts fell significantly from baseline at every timepoint in both groups, from roughly two drops per eye preoperatively to between 0.5 and 0.6 at two years, with no significant difference between devices. Baseline characteristics were well matched except for ethnicity, which was more predominantly Chinese in the Hydrus group, and visual field mean deviation, which was worse by about 2 decibels in the Hydrus group, indicating somewhat more advanced disease. Nearly all eyes, 96.1 percent of iStent and 100 percent of Hydrus, underwent combined phacoemulsification cataract surgery.

How do these results compare with landmark trials in non-myopic eyes? The investigators found that their cohort fared worse. Samuelson and colleagues reported 63.2 percent of primary open-angle glaucoma subjects achieving a pressure of 18 mmHg or less without drops two years after iStent inject implantation, and the HORIZON trial reported 49.5 percent achieving the same five years after Hydrus implantation, with 84 percent and 78 percent attaining drop-freedom at two years respectively. In the present study, only 31.7 percent of iStent eyes and 43.3 percent of Hydrus eyes reached 18 mmHg or less without drops, and drop-freedom stood at 38.5 and 48.7 percent. The authors caution that direct comparison is limited by differences in study populations, surgical protocols, and outcome definitions, particularly the medication washout periods used in the randomized trials. They also point to their cohort’s low baseline medicated pressure of about 15 mmHg, which leaves little room for percentage reduction, and its more advanced disease stage as likely contributors. Similar patterns emerged in ab-interno trabeculotomy studies, where high myopes achieved qualified success rates of 35 percent versus 65 percent in non-high myopes at twenty-four months.

The study has important limitations that temper its conclusions. Its retrospective design meant data could only be standardized at the scheduled follow-up visits, preventing precise determination of failure dates, and the fixed sample size precluded an a priori power calculation. Preoperative pressures were measured without a medication washout, potentially introducing inaccuracy, and multivariable adjusted models could not converge because of complete separation in ethnicity and standalone surgery variables, so only unadjusted results are reported. Patients in the Hydrus group came from a single center where most surgeries were performed by two surgeons, while iStent patients came predominantly from one of the three centers, raising the possibility of center- and surgeon-specific bias. The authors suggest that in highly myopic eyes, where the main resistance to aqueous outflow may lie distal to an enlarged Schlemm’s canal and where traditional incisional surgery carries elevated risks, trabecular bypass procedures may still represent a clinically relevant and safer option, even if the pressure-lowering effect remains modest. More research into pressure-lowering options tailored to the highly myopic eye, they conclude, is clearly needed.

Subject of Research: Surgical outcomes of trabecular bypass MIGS devices in highly myopic eyes with glaucoma

Article Title: Surgical outcomes of trabecular micro-bypass minimally invasive glaucoma surgery devices in eyes with high myopia: a 24-month retrospective multicenter cohort study

Article References: Ang, B. C. H., Wong, N. S. Q., Kochar, A., Lor, S., Phang, L. C., Htoon, H. M., Tan, J., Lawlor, M., Ramesh, P. V., Jung, Y., Yap, Z. L., Ng, S. R., & Chong, R. S. (2026). Surgical outcomes of trabecular micro-bypass minimally invasive glaucoma surgery devices in eyes with high myopia: a 24-month retrospective multicenter cohort study. Eye and Vision, 13(1), Article 40. https://doi.org/10.1186/s40662-026-00512-1

Image Credits: AI Generated

DOI: 10.1186/s40662-026-00512-1

Keywords: glaucoma, MIGS, iStent inject, Hydrus microstent, high myopia, intraocular pressure, trabecular bypass, cataract surgery, ophthalmology, retrospective cohort study, Schlemm's canal, surgical outcomes