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C. Kniestedt, M.T. Nee, R.L. Stamper; Comparative Responses of Dynamic Contour Tonometry, Goldmann Applanation Tonometry and Pneumotonometry on Hydrated and Dehydrated Human Cadaver Eyes . Invest. Ophthalmol. Vis. Sci. 2003;44(13):84.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare intraocular pressure (IOP) measurements obtained by Dynamic Contour Tonometry (DCT), Goldmann Applanation Tonometry (GAT), and pneumotonometry (PTG) and intracameral manometry in human cadaver corneas of different hydration conditions. Methods: 10 freshly enucleated human cadaver eyes were de-epithelialized. A tube was placed in the anterior chamber and connected to a transducer and to a bottle system filled with balanced salt solution. The pressure in the eye was then altered between 5mmHg and 58mmHg by changing the height of the bottle. Central Corneal Thickness (CCT) and IOP measurements were obtained with DCT, GAT, and PTG at each manometric pressure reading. Immediately after the trial the same corneas were dehydrated with Dextran 20% until a relatively stable CCT was achieved and the same measurement regimen was repeated. DCT was recently introduced by Kanngiesser and Robert. The tonometer curvature forces the external surface of the cornea into a shape that allows equal pressures on both sides of the cornea wich is then measured with a pressure sensitive tip. DCT is hypothesized to be less dependent on CCT and hydration conditions of the cornea and to measure IOP more acurately than other types of external tonometry based on applanation and indentation. Results: Hydrated human cadaver corneas presented with a CCT of 902µm±128µm, whereas the dehydrated corneae measured 449µm±46µm. In the clinically significant pressure range of 8 through 38mmHg (bottle height 10 through 50cm), DCT measured 0.49±0.48mmHg and 0.34±0.48mmHg higher before and after dehydration as compared to manometric readings. GAT showed consistently lower values of -3.50±2.30mmHg and-3.13±1.10mmHg. Similar low results were obtained with PGT, namely -4.16±2.40mmHg and -3.66±2.18mmHg for the hydrated and dehydrated corneal condition respectively. The thinning (mean 443±90µm) based on the dehydration process accounted for an average measurement change of -0.15±0.66mmHg (Linear correlation: y=0.0011x-0.3625) for DCT, +0.37±2.24mmHg (y=0.0044x-2.4508) for GAT, and +0.50±2.04mmHg (y=0.0078x-4.1339) for PTG. Conclusions: In this in vitro study DCT does indeed indicate IOP that is closer to the true manometric levels than GAT or PTG in both hydrated and dehydrated human cadaver corneae. The accuracy of DCT might be less dependent on corneal thickness and hydration. DCT data were obtained more easily and with less observer bias than data aquisition with GAT and PTG which had larger scatter. In vivo trials are indicated to see if the apparent advantage of DCT in clinical situations persists.
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