Letter to the Editor: Cost-analysis of Surgical Intraocular Pressure Management in Glaucoma.

We write in reference to “Cost analysis of surgical intraocular pressure management in glaucoma” by Elhusseiny et al.1 The authors address an important issue, aiming to quantify the value of clinically effective glaucoma surgical procedures. However, they present average cost-effectiveness ratios (ACERs), not incremental cost-effectiveness ratios (ICERs), which is what Health Technology Assessment (HTA) agencies consider when making coverage decisions. Confusion between ACERs and ICERs is common but can lead to inappropriate policy recommendations.

As an example of the ICER concept, every product is positioned in relation to its next most costly alternative, and a decision is made as to whether the additional benefits are worth the costs. Figure 1 provides a graphical example of the per-person cost and effectiveness in terms of quality-adjusted life years (QALYs) saved of usual care and 5 interventions, ordered from lowest to highest cost. The slope of the line segments illustrates the ICERs for each strategy. The figure demonstrates that Strategy 1 should never be employed; at a cost of $7000, one could obtain greater QALYs by offering a mix of usual care and Strategy 2. Importantly, this holds true even though Strategy 1 has a better ACER than Strategies 4 and 5. This example is how HTA agencies make decisions about the value of new medical products.

FIGURE 1

Example cost-effectiveness frontier. QALY indicates quality-adjusted life year.

Elhusseiny and colleagues conclude that “conventional glaucoma surgeries and SLT surgery were the most cost-efficient surgical methods to lower intraocular pressure (IOP) compared with the various microinvasive glaucoma surgery options.” However, this conclusion can only be made with knowledge of ICERs and a decision-maker’s willingness-to-pay for additional health gains. This can be illustrated using lines V1 and V2 in Figure 1. If the decision-maker were willing to pay a maximum of $50,000 for a unit gain in QALYs (in the case of V2), then Strategy 3 would be the preferred option. In the case of V1 ($100,000/QALY), where the decision-maker has a higher willingness-to-pay for 1 U of QALYs, as shown by its steeper slope than that of V1, Strategy 4 would be preferred.

Elhusseiny and colleagues present health gains in term of reductions in IOP. HTA agencies almost universally rely on QALYs because there are well-established benchmarks for what represents good value for money using this metric; no such benchmark exists for cost per IOP reduction. Since policymakers understand cost/QALY, it is important to convert the cost/IOP into cost/QALY and consider a lifetime perspective. A long-term perspective is needed as the benefits of better IOP in the short term may be outweighed by some of the secondary complications and subsequent treatments that may not materialize until years later with conventional glaucoma surgeries.

HTA agencies also recognize that some procedures may be more clinically appropriate than others and that this decision depends on severity of glaucoma, baseline IOP (as IOP goals differ by glaucoma severity2) as well as other factors specific to the individual patient, such as patient’s age, employment status, and lifestyle. Given the importance of the topic, future studies regarding the relative merits of options should build on the excellent work of Elhusseiny and colleagues to produce ICERs using cost/QALY while taking a lifetime perspective and with analyses for select subgroups of patients.