Association between mean intraocular pressure, disease stability and cost of treating glaucoma in Canada.

Purpose: A retrospective analysis determined the association between intraocular pressure (IOP) control levels (mean and last IOP) and disease stability, and the association between IOP and yearly treatment cost in primary open angle glaucoma (POAG).
Methods: Data were collected from POAG patients, referred to a tertiary glaucoma clinic. All IOP measurements, visual field mean deviation (VF) scores, physicians' impressions, and resources used (physician visits, procedures, and medications) were recorded and costed using standard resource unit cost lists from the Ministry of Health's perspective. Patients were categorized by the average VF score of their first three visits [mild (< 5 dB), moderate (> or = 5 dB to < 12 dB) and severe (> or = 12 dB)]. Pearson's r quantified the association between IOP control levels and stability, where stability was defined by the physician's subjective impression of the patient's disease. Spearman's rho was determined to quantify association between mean IOP and yearly treatment cost within VF categories.
Results: Four hundred and eleven charts were reviewed of which 265 were acceptable for analysis. A negative relationship was determined between the probability of reaching stability and mean IOP in all three VF severity groups. Pearson's r was -0.68 (p < 0.001), -0.72 (p < 0.001), and -0.52 (p < 0.001) for the mild, moderate, and severe groups, respectively. A similar correlation was determined between the last measured IOP and stability. Pearson's r was -0.49 (p < 0.001), -0.80 (p < 0.001), and -0.65 (p < 0.001) for the mild, moderate and severe groups, respectively. A positive relationship was reported between mean yearly costs and IOP. Spearman's rho between mean yearly costs and mean IOP was 0.11 (p = 0.28), 0.23 (p < 0.05), and 0.26 (p < 0.05) for each respective VF level.
Discussion and Conclusion: Lower IOP control levels are associated with higher probabilities of stability. In addition, lower IOP control levels are associated with lower costs of managing POAG in patients either with moderate VF loss or with severe VF loss. Economic burden increased with increasing disease severity.