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G. B. Skjold, P. A. Naevdal, O. K. Volden, M. Nilsen, P. O. Lundmark; The Association Between Intraocular Pressure and Optic Disk Evaluation Using the ISNT Rule in 40 to 79 Yrs Old Patients Seen in Optometric Practice. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3622.
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To investigate the association between intraocular pressure (IOP) and the outcome of optic disk assessments using the ISNT rule in healthy patients seen in optometric practice.
Consecutive patients over the age of 40 yrs and with no known general- or ocular pathology were enrolled into the study from 4 optometric practices in Norway and Sweden during a period of 9 months. The sample was stratified by age group (40-49; 50-59; 60-69 and 70-79 yrs) and ISNT rule outcome (positive or negative). Subjects underwent a full optometric examination including stereoscopic assessment of the optic disk where the outcome was considered negative if the width of the neuroretinal rim obeyed the ISNT rule (widest Inferiorly followed by Superiorly, Nasally and Temporally) and positive in other cases, followed by measurements of the IOP (non-contact tonometry) and central corneal thickness (CCT). The vertical size of the disk was measured. Ocular parameters were analyzed for one eye per subject. Selection was randomized when both eyes were equally classified. In other cases the eye with positive outcome was selected. Odds ratio (OR) was used to assess the association between IOP and the outcome measure. Stratified analysis (Chi-square) was employed to investigate the effect of age, sex, CCT, refractive error (myopia or hyperopia) and disk size on the association. IOP was dichotomized at a cutoff corresponding to the 75th percentile, whereas numeric covariables were categorized at cutoffs corresponding to the 33rd and 66th percentile, respectively.
A total of 159 patients (F: 90, mean age 57.1 yrs, range: 40 - 79) were included. IOP was significantly higher in patients with a positive outcome using the ISNT rule (16.9 vs. 15.4 mmHg, p=0.014), corresponding to a crude OR of 2.2 (CI 1.1-4.8). In stratified analyses the association between IOP and positive outcome was significant for the following covariables: age group 50-59 (OR 4.2 CI 1.0-17.1), cornea thickness <548 micron (OR 6.6 CI 1.2-34.7), males (OR 7.7 CI 1.6-38.0), vertical disk size < 1.6 mm (OR 4.8 CI 1.3-18.3), and myopia (OR 6.0 CI 1.2-30.1).
Optic disks that did not obey the ISNT rule were associated with higher IOP than disks that conformed to the rule. Results indicate that this association may be strengthened by male gender, age in the fifties, myopia, thin corneas and small optic disks. Further research investigating the independent effect of these factors is warranted.
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