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F. A. Medeiros, L. M. Alencar, D. Chao, A. Tafreshi, P. A. Sample, C. Bowd, L. M. Zangwill, R. N. Weinreb; The Relationship Between Intraocular Pressure and Rates of Progressive Visual Field Loss in Glaucoma. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5831.
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To evaluate the relationship between intraocular pressure and rates of progressive visual field loss in glaucoma patients followed over time.
This was an observational cohort study that included 432 eyes of 238 patients recruited from a prospective longitudinal study (Diagnostic Innovations in Glaucoma Study - DIGS). All patients were diagnosed as having primary open angle glaucoma at baseline based on the presence of repeatable visual field defects on standard automated perimetry (SAP) and/or glaucomatous optic neuropathy on optic disc stereophotographs. Rates of progressive visual field loss were measured by the Visual Field Index (VFI). Functional data analysis (FDA) was used to evaluate the relationship between IOP and longitudinal changes in VFI scores. For each eye, smooth monotone decreasing functions using B-splines were used to model VFI scores over time. The first derivatives of these functions represented the rates of VFI change over time. IOP trajectories over time were also modeled using cubic splines. The relationship between IOP, central corneal thickness and disease severity (measured by VFI) with rates of VFI change was evaluated by mixed models. A historical model was also constructed to evaluate the influence of IOP levels obtained during the preceding 1 year of follow-up on the subsequent rates of VFI change by integrating the IOP trajectories at annual intervals.
Average follow-up time was 6.0 years (median: 4.9, first quartile: 2.7, third quartile: 9.2). Higher levels of IOP during follow-up were significantly associated with higher rates of visual field loss. Each 1 mmHg higher IOP was associated with 0.20 units/year greater loss of VFI. Eyes with thin corneas (P = 0.026) and more severe disease (P = 0.001) had significantly higher rates of progression. There was a significant interaction between the IOP effect and disease severity (P < 0.001). In eyes with severe disease, each 1 mmHg change in IOP was related to greater changes in the rates of progression compared to eyes with less severe damage. In the historical model, IOP levels during the preceding year were significantly related to the subsequent rate of VFI change (P = 0.002).
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