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A. de Saint Sardos, A. Kamdeu Fansi, M. Chagnon, P.J. Harasymowycz; An Assessment of Intraocular Pressure Corrected for Central Corneal Thickness as a Screening Tool for Primary Open Angle Glaucoma in a High Risk Population . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3421.
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To assess the validity of IOP corrected for CCT as a screening tool for POAG in various at–risk groups in an urban Canadian population.
Study data was gathered during a community based, high–risk glaucoma screening clinic conducted in Montreal, Canada between Oct 2003 and Sept 2005. Two hundred and seventy four patients underwent a complete ophthalmic examination including visual acuity, ultrasonographic corneal pachymetry (the average of three separate measurements), intraocular pressure measurement by Goldmann applanation tonometry, gonioscopy, slit lamp and dilated fundoscopic examination, as well as non mydriatic photography of the optic nerve. Outcome measures included IOP, CCT and the presence of glaucomatous optic nerve damage as confirmed by a consensus of three disc readers. Five different published algorithms were used to correct IOP for CCT for each eye. The corrected IOPs of patients with glaucoma were compared to those of glaucoma suspects as well as to participants without glaucoma and not suspect. Statistical analyses including ANOVA, student t–test, multivariate analysis and AROC were conducted using GraphPad Prism and SPSS software.
A total of 516 eyes with an average IOP of 16.4mmHg and an average CCT of 550.4µm were included in the study. There were 31 eyes diagnosed with POAG (prevalence 6.0%) and 68 eyes that were suspect for glaucoma. Prior to correcting for CCT, an IOP greater than 21mmHg was determined to be highly specific (99%) with a sensitivity of 12%, a positive predictive value of 43% and a negative predictive value of 95% as a screening test for POAG. The area under the receiver operating characteristic (AROC) for the right and left eyes were 0.57 and 0.51 respectively. Depending on the correction factor used, the AROC varied significantly from 0.51–0.70 post adjustment of IOP for CCT. The use of 21mmHg as a screening test cut–off point, post adjustment of IOPs for CCT was not significantly more sensitive and no less specific than for unadjusted IOPs.
Correcting IOP for CCT does not improve its validity as a screening tool for glaucoma in a high–risk urban population.
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