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Comment by Augusto Azuara Blanco on:

20389 Cost-effectiveness of treating ocular hypertension, Stewart WC; Stewart JA; Nassar QJ et al., Ophthalmology, 2008; 115: 94-98

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This report by Stewart et al. examines the cost-effectiveness of treating ocular hypertension (OH), using results from two major randomised controlled trials, the Ocular Hypertension Treatment Study (OHTS), and the Early Manifest Glaucoma Trial (EMGT). We usually define OH as an intraocular pressure of > 21 mmHg (the approximate 95^th percentile of IOP in a European-derived population) in the absence of glaucoma. Using the OHTS dataset changes the definition to that used in the OHTS; i.e., an intraocular pressure of between 24 and 32 mmHg in the absence of glaucoma. Similarly, the definition of glaucoma changes to early manifest or pre-perimetric open-angle glaucoma. This is important as it changes how we might apply the results to clinical practice. This question asked was this: Compared to not treating OHTS ocular hypertension (OOH) until glaucoma develops, what is the direct medical cost in the U.S.A. (in USD) (per quality-adjusted life-year) of treating at baseline to prevent a case of glaucoma developing?

Clinical decisions to treat ocular hypertension are complex and usually take into account a patient's estimated individual risk and preferences as well as the culture of healthcare in that region

There is no benchmark which allows us to say whether doing some-thing is cost-effective. The paper uses the United Kingdom's National Institute for Health and Clinical Excellence's (NICE) concept of a "most plausible incremental cost-effectiveness ratio (ICER)" under which cost-effectiveness would be the main determinant of whether a technology would be an effective use of resources for the UK National Health Service. For treating all OOH, the ICER of $89 072 is well above the $50 000 NICE limit. However the ICER falls greatly as baseline risk increases. Older people with higher IOPs, thinner corneas and larger vertical cup/disc ratios are more likely to develop glaucoma and therefore more likely to benefit from treatment, with ICERs all under $50 000. For someone of average age (56 yrs) with average IOP (25mmHg) and a cup/disc ratio of 0.4, the ICER when CCT was less than 493 microns fell to $15,567. While the costs of treatment can be calculated, the loss of quality of life from moving from OH to glaucoma is more difficult to determine.

The paper makes estimates from the literature while recognizing the paucity of published information. This is an area where much more research is needed. Clinical decisions to treat ocular hypertension are complex and usually take into account a patient's estimated individual risk and preferences as well as the culture of healthcare in that region. At a wider level, the expending of resources on treating ocular hyper-tension takes away resources from other endeavours. Stewart's paper does not tell us whether treating ocular hypertension is cost-effective; it can not. But it does bring home the importance of risk factor analysis in health economics and reminds us that the benefits we can achieve for our patients for a particular cost are not always the same.

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