Glaucoma Stent Reviews Find Cost-Effectiveness Hinges on Perspective and Time Horizon

A systematic review of model-based economic evaluations has found that adding an iStent-family trabecular micro-bypass stent to cataract surgery is projected to be cost-effective for mild-to-moderate open-angle glaucoma in every published analysis meeting its criteria — but that this uniform conclusion rests on a narrow, largely industry-funded evidence base built on incremental quality-of-life gains so small that the reported ratios are unstable. The review, published in Cost Effectiveness and Resource Allocation, examined how the analytic perspective and time horizon chosen by each model shape the decision the evidence can actually inform.

The reviewer searched PubMed, Embase, the Cochrane Library and Web of Science on 27 July 2026 without date, language or publication-type restriction. Of 418 records identified and 293 remaining after de-duplication, eight economic evaluations from eight countries met the eligibility criteria. All eight compared an iStent device implanted concurrently with cataract surgery against cataract surgery alone in adults with mild-to-moderate open-angle glaucoma. Seven used a cohort Markov model and one an individual-patient Monte Carlo microsimulation of 500,000 simulated patients. Reporting followed PRISMA 2020, and the reporting quality of each included study was appraised item-by-item against the CHEERS 2022 checklist.

All eight evaluations reported a favourable base-case result. The reported incremental cost-effectiveness ratios included €1,154 per quality-adjusted life year in France, €12,676 in Spain, €13,037 in Italy, €10,955 for two stents and €15,673 for one in Germany, JPY 1,430,647 in Japan and A$2,430 in Australia — the last derived from an incremental cost of A$177 and a gain of 0.0726 QALYs. Two analyses reported outright dominance, meaning lower cost with greater effect: a Canadian study reported a ratio of −CAD 16,691 with a 73.7% probability of cost saving, and a United States study reported the intervention costing USD 4,809.39 less while yielding 0.17 more QALYs than cataract surgery alone.

A feature common to the entire evidence base qualifies those headline numbers. The incremental QALY gains were small throughout, ranging from approximately 0.005 to 0.17 — from negligible to roughly two months of full-health-equivalent time over a lifetime. Because the ratio places this quantity in the denominator, small differences in modelled effectiveness produce very large differences in the reported ICER. The German analysis illustrates this directly: the same procedure yields €10,955 per QALY in moderate disease but €60,269 per QALY in advanced disease, where the utility gain is smaller while the cost is unchanged. The review concludes that the reported ratios should not be treated as stable quantities suitable for comparison between studies.

Time horizon also demonstrably affects the conclusion. The Canadian evaluation reported the same model over several horizons: the intervention was dominant over a lifetime and over a 15-year base case, but at five years the cost-saving result did not persist, with an incremental cost of CAD 446.90 and a ratio of CAD 32,227.80 per QALY — still below that study’s CAD 50,000 threshold, but with substantially wider uncertainty. A Spanish evaluation showed the same direction, reporting €12,676.48 per QALY over a lifetime base case against €15,699.56 in a 15-year scenario. The reason is visible in the cost breakdown: the additional primary surgery cost falls in the first year, whereas the medication saving accumulates across the whole horizon.

Six of the eight evaluations were funded by the device manufacturer, Glaukos Corporation, and in five one or more co-authors were manufacturer employees. Moreover, six of the eight modelled iStent inject, and their clinical-effect inputs were derived largely from the same two-year pivotal trial. The apparent convergence across the economic models therefore does not represent independent replication. Extrapolation beyond the two-year trial follow-up rests on assumption in every model; some assumed the treatment effect declines by 5% annually to year ten with no effect thereafter, while others extrapolated efficacy for ten years or over a lifetime without stating an explicit projection method.

The review’s central structural observation concerns analytic perspective. Six studies adopted a payer or health-system perspective and two a societal perspective; no evaluation adopted a provider or hospital-budget perspective, and every base-case horizon was 15 years or longer — five lifetime, one 35 years and two 15 years. The device cost is incurred at the time of surgery, while the modelled savings, principally reduced topical medication use and deferred subsequent surgery, accrue over decades. Where the device is not separately reimbursed, an annually budgeted surgical service may bear the marginal cost without recovering any of the modelled return within its own planning horizon. No included model reports the distribution of costs and savings between budget holders.

Several further limitations temper the findings. Discount rates ranged from 1.5% to 5% where stated, and at every rate applied most of the present value of a constant annual saving over fifteen years falls after year five — already beyond any observed follow-up. No evaluation modelled long-term structural change in medication prices, prescribing practice or competing alternatives, and none applied the systematic optimism adjustments required in some public-sector appraisal guidance. No study reported a pre-specified health economic analysis plan, price years were missing or unverifiable in two studies, and all eight evaluations derive from high-income health systems, so generalisation to middle- or low-income settings is not supported. The review was also conducted by a single reviewer without prospective PROSPERO registration.

The review’s conclusions are deliberately conditional. The included peer-reviewed models generally project that adding an iStent-family device to already planned cataract surgery can be cost-effective over long horizons, but that projection depends on sustained medication reduction, on extrapolated glaucoma progression and on local device and treatment costs. Direct evidence that the modelled long-term clinical benefit is realised in practice and offsets the acquisition cost remains limited. The evidence applies to adults with mild-to-moderate open-angle glaucoma already scheduled for cataract surgery in high-income systems; it does not address secondary open-angle glaucoma, angle-closure disease or standalone implantation. The reviewer identifies a concrete direction for future work: a budget-impact analysis from the provider perspective over a one-to-three-year horizon, reporting explicitly which budget carries each cost and each saving, would address a decision that the included cost-utility analyses do not.

Subject of Research: Cost-effectiveness of iStent trabecular micro-bypass stenting combined with cataract surgery in mild-to-moderate open-angle glaucoma

Article Title: Cost-effectiveness of iStent-based trabecular micro-bypass stenting combined with cataract surgery in mild-to-moderate open-angle glaucoma: a systematic review of analytic perspectives and time horizons

Article References: Drobin, D. (2026). Cost-effectiveness of iStent-based trabecular micro-bypass stenting combined with cataract surgery in mild-to-moderate open-angle glaucoma: a systematic review of analytic perspectives and time horizons. Cost Effectiveness and Resource Allocation, 24(1), Article 128. https://doi.org/10.1186/s12962-026-00846-6

Image Credits: AI Generated

DOI: 10.1186/s12962-026-00846-6

Keywords: glaucoma, iStent, cataract surgery, cost-effectiveness, systematic review, MIGS, QALY, health economics, trabecular micro-bypass, analytic perspective, time horizon, industry funding