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Daniel R. Agarwal, Joshua R. Ehrlich, Mitsugu Shimmyo, Nathan M. Radcliffe; Effect of Correction Formulas for Corneal Properties on the Magnitude of Intraocular Pressure Reduction from Topical Prostaglandin Therapy. Invest. Ophthalmol. Vis. Sci. 2011;52(14):664.
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Investigators have proposed distinct formulas to correct IOP for corneal bio-structural and mechanical properties including central corneal thickness (CCT) and corneal hysteresis (CH). We sought to determine whether the use of several published corneal correction formulas would result in different measurements of the magnitude of IOP reduction from ocular hypotensive therapy.
61 consecutive patients with open-angle glaucoma who were treatment naïve and initiated on a prostaglandin analog (PGA) underwent examination with the Ocular Response Analyzer (ORA; Reichert, Corp., Buffalo, NY) at baseline (untreated) and at follow-up (treated). IOP correction formulas included ORA-generated corneal compensated IOP (IOPcc) and three published formulas(1-3) to adjust for the impact of CCT, assuming either a linear(1,2) or logarithmic(2,3) relationship between corneal properties and IOP.
Goldmann-correlated IOP (IOPg) unadjusted for corneal properties was reduced by 4.0 mm Hg (22.3%) from 17.9 mm Hg at baseline to 13.9 mm Hg after treatment (p<0.001). Baseline CCT was 542.4 µm and baseline CH was 9.5 mm Hg. IOPg corrected for CCT using the three cited formulas declined by 4.01, 4.01, and 4.05 mm Hg respectively while IOPcc declined by 4.28 mm Hg. Compared to unadjusted IOPg, there was no significant difference in the amount of IOPg reduction with adjustment for corneal properties (p≥0.15, pairwise comparisons), nor were there significant differences in the magnitude of IOPg reduction between correction formulas (p≥0.15, pairwise comparisons).
Adjustment of IOP for corneal properties results in significantly different IOP values, however correction formulas did not significantly impact the magnitude of IOP reduction following initiation of PGA therapy. This study suggests that cross-sectional correction of IOP could impact the determination of target IOPs but that IOP correction may be less useful in longitudinally gauging treatment response.1. Kohlhaas M, et al. Arch Ophthalmol. 2006;124(4):471-476.2. Ko Y, et al. Eye. 2004;19(3):327-332.3. Shimmyo M, et al. Am J Ophthalmol. 2003;136(4):603-613.
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