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D. C. Pye, W. M. Lau; The Effect of Corneal Edema on Ocular Response Analyser and Goldmann Tonometry Measurements. Invest. Ophthalmol. Vis. Sci. 2010;51(13):567.
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To investigate the changes in Goldmann Applanation Tonometry (GAT) and Ocular Response Analyser (ORA) measurements (corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated IOP (ORAg) and corneal-compensated IOP (ORAcc)) with contact lens induced corneal edema.
25 healthy normals (age 23±2 years) had central corneal radius (CCR), ORA, GAT and central corneal thickness (CCT) measurements performed in both eyes before a thick, soft hydrogel contact lens was worn with eye closure for 2 hours in one eye. Measurements were repeated immediately after lens removal and every 20 minutes thereafter for the following hour.
The experimental and control eyes behaved asymmetrically over time (repeated measures ANOVA, p<0.05) for all variables except CCR. The changes in GAT, ORAg and ORAcc were similar (repeated measures ANOVA, p>0.05). Means and standard deviations for GAT, CCT, CH and CRF in the experimental eye, corrected for changes in the control eye at each time, are given in the Table below. After accounting for the fluctuations in the control eye, changes in GAT could be predicted by changes in CRF (linear mixed models, 0.65±0.27 mmHg change in GAT per mmHg CRF change, p<0.05), but not by changes in CCT, auto-keratometry or CH (all p>0.05).
The GAT, ORAg and ORAcc overestimations due to contact lens induced corneal edema were not related to the level of corneal swelling as measured by CCT. GAT errors could be partially predicted by CRF, but not CH.
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