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Georgios A. Kontadakis, Alexandros Pennos, Iro Pentari, George D. Kymionis, Ioannis G. Pallikaris, Harilaos S. Ginis; Corneal Edema And Tonometry Errors: An In-vitro Comparative Evaluation Of Dynamic Contour Tonometry, Goldman Applanation Tonometry And Tonopen Xl. Invest. Ophthalmol. Vis. Sci. 2011;52(14):681.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate in vitro the accuracy of Dynamic Contour Tonometry (DCT), Goldman Applanation Tonometry (GAT) and TonoPen XL (TXL) in edematous corneas.
Twenty porcine eyes were obtained from a local abattoir. Epithelium was mechanically debrided and total globes were divided in 4 groups. Groups were immersed in glycerin solutions of 35%, 40%, 50% and 60% concentration for 3 hours in order for the corneal hydrations to reach equilibrium. Subsequently, globes were mounted in a purposely-made holder and intraocular pressure was regulated hydrostatically through anterior chamber cannulation. The IOP of each globe was measured by means of DCT, GAT, and TXL while adjusting true IOP to 33mmHg and 50mmHg by the height of the saline column. Corneal ultrasound pachymetry was performed.
Mean corneal thickness in our group of corneas was 914.5±33,3µm (range 730-1015µm). All corneas were in edematous condition and thickness was significantly correlated with glycerin concentration (p<0.001). The IOP measurements taken under IOP of 33mmHg with the three methods were correlated to each other (p<0.001). The measurements taken under IOP of 50mmHg were not correlated to each other. No measurement was correlated to corneal thickness. In true IOP of 33mmHg, GAT and DCT significantly underestimated true IOP (mean GAT: 14.7±4.8mmHg, p<0.001, mean DCT: 21.6±6.8, P<0.001). TXL also underestimated but difference was not statistically significant (TXL: 27.9±9.7, p=0.064). In true IOP of 50 mmHg all three methods significantly underestimated true IOP (GAT: 17.6±5.3mmHg, p<0.001, DCT: 26.8±6.3mmHg, p<0.001, TXL: 35.6±8.4mmHg, p<0.001). The error in measured IOP for each method (true minus measured IOP) was significantly correlated to true IOP (p<0.001).
GAT, DCT and TXL underestimate IOP when measured under edematous conditions. TXL showed better accuracy than the other methods especially in lower true IOP. The measurement error increases when true IOP increases in all three methods.
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