Should all ocular hypertension cases be treated?

At the annual meeting of the Association for Research in Vision and Ophthalmology, Steven M. Kymes, PhD, an outcomes researcher with the OHTS and instructor in the Department of Ophthalmology and Visual Sciences at Washington University School of Medicine in St. Louis, reported the results of an economic evaluation examining the cost-effectiveness of treatment of ocular hypertension based upon the patient's risk of developing primary open-angle glaucoma (POAG). Dr. Kymes and his colleagues found treatment of people with at least a 2% annual risk of the development of POAG was cost effective, leading him to assert that a management strategy delaying treatment of all people with ocular hypertension until there is evidence of glaucoma-related visual field loss or nerve damage is an unnecessarily conservative approach.

An economic model

Dr. Kymes explained that based upon the distribution of risk factors in OHTS, treating those with a 5% or greater annual risk represents about 10% of patients with IOP ≥24 mm Hg in at least one eye (the OHTS definition of ocular hypertension), and those with 2% or greater annual risk represents about 30% of patients meeting that criterion.

He later explained that because OHTS was not a population-based study, this prevalence may not reflect that seen in clinical practice.

In their evaluation, the OHTS researchers used a cost-utility approach, Dr. Kymes explained.

In this approach the investigators considered not only the cost of treatment and the cost saved by avoiding progression to blindness, but also the impact of disease on the patient's quality of life. In the model, quality of life is measured based upon "utilities," which when multiplied by the patient's expected length of life result in a measure called the quality-adjusted life year (QALY).

To illustrate this formula, he cited an example of patients with a visual acuity in the better eye of 20/200 or worse, which represents a 35% loss of quality of life. Therefore, a year of life spent in blindness carried the value of 0.65, and if the blindness could be prevented, the patient would gain 0.35 QALY.

The outcome measure in cost-utility analysis is the incremental cost-effectiveness ratio (ICER), which is calculated as the additional cost of treatment divided by the incremental gain due to treatment. In the investigation conducted by the OHTS team, the ICER would be the increased cost of treatment to prevent glaucoma divided by the quality of life gained due to the prevention of glaucoma.

In their model, the investigators used data from the OHTS including the incidence of POAG, benefit of treatment, and cost of medication. They recognized that efforts to maintain decreased IOP would require changes in medication or addition of more medications.