Accuracy of dynamic contour tonometry compared with applanation tonometry in human cadaver eyes of different hydration states

Abstract

In an experimental laboratory investigation we compared intraocular pressure (IOP) measurements obtained by dynamic contour tonometry (DCT), Goldmann applanation tonometry (GAT), and pneumatonometry (PTG) with intracameral manometry on human cadaver corneas of different hydration conditions. Ten freshly enucleated eyes were de-epithelialized. Two tubes were placed in the anterior chamber in opposite directions and connected to a transducer and to a bottle system filled with balanced salt solution. The pressure in the eye was then adjusted between 5 mmHg and 58 mmHg by electronically altering the height of the bottle. Central corneal thickness (CCT) was registered and IOP measurements were obtained with DCT, GAT, and PTG at each manometric pressure reading. Immediately after the trial the same corneas were artificially dehydrated and the same measurement regimen was repeated. In the pressure range defined by the bottle height 10-50 cm, IOP values measured by DCT were 0.50 mmHg (95% CI=0.40-0.60) and 0.36 mmHg (95% CI=0.25-0.47) higher than manometric readings before and after dehydration, respectively. GAT showed consistently lower values than manometry, the difference being -3.48 mmHg (95% CI=-3.91 to -3.05) and -3.14 mmHg (95% CI=-3.39 to -2.89), respectively. Similar results were obtained with PGT, namely differences of -4.75 mmHg (95% CI=-5.21 to -4.29) and -3.98 mmHg (95% CI=-4.48 to -3.48) for the hydrated and the dehydrated corneal condition, respectively. Only DCT showed no significant change in accuracy between hydrated and dehydrated corneas. In this in vitro study DCT values for IOP were significantly closer to the manometric reference pressure than those obtained using GAT and PTG, independent of the state of corneal hydration.