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Reena Vaswani, Annapurna Singh; Importance of Defining a Target Intra-Ocular Pressure: a Meta-Analysis. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5052.
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To analyze the utility of target IOP in the management of early primary open angle glaucoma (POAG).
A review of literature was performed using the Pub Med database, key words including target IOP, goal IOP, treatment, and glaucoma progression. The inclusion criteria included randomized controlled clinical trials with long-term follow up. Techniques of meta-analysis were utilized to compare the results of studies with a target IOP versus those without target IOP, and were able to analyze whether treatment had a significant effect versus controls in each group of studies. There was evidence of heterogeneity, utilizing the Q statistic (p < 0.01), in the group without target IOP, so a random effects model was used for each meta-analysis. Additionally, an estimate of the risk difference (RD) for progression was calculated for each group.
The literature search revealed five randomized controlled clinical trials that analyzed the benefit of IOP reduction to prevent visual field loss progression in early POAG. Of the five trials, three employed a target IOP. The Ocular Hypertension Treatment Study (OHTS) treated with a goal reduction of IOP by 20% from baseline. The Collaborative Normal Tension Glaucoma study group (CNTGS) employed a treatment goal of 30% reduction in IOP. The Collaborative Initial Glaucoma Treatment Study (CIGTS) employed a formula to calculate target IOP based on baseline IOP, visual field, and optic disc appearance. In contrast, the Early Manifest Glaucoma Trial (EMGT) and the European Glaucoma Prevention Study (EGPS) failed to define IOP reduction goal. Because the CIGT study did not have a control group, it was excluded from these analyses. In the target IOP group (N = 1,781) the RD was estimated to be 8.01% (95% CI : 1.81% - 14.22%) with p = 0.01 for rejection of the null hypothesis. In the group without target IOP, (N = 1,332) the RD was estimated to be 8.17% (95% CI : -7.89% - 24.22%) with p = 0.32.
The trials that utilized the concept of target IOP were found to have greater success in preventing progression of visual field loss when compared with the trials that did not have target IOP. The RD of progression between the control and treatment groups was significantly lower for the treatment arm compared to the control arm in the target IOP group. The RD of progression was not significantly different in the treatment versus control arms for the no target group. Additionally, the RD was higher in the no target group compared to the target group. This review of data suggests that target IOP is in fact an important clinical parameter, and utilization of a target IOP can significantly lower the risk of progression of POAG.
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