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T. S. Romppainen, L. M. Bachmann, C. Kaufmann, C. Kniestedt, M. Mrochen, M. A. Thiel; Effect of Riboflavin-UVA Induced Corneal Collagen Crosslinking on Intraocular Pressure Measurement. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1848.
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Corneal collagen crosslinking (CCC) with riboflavin and ultraviolet A irradiation has recently been introduced for the treatment of corneal ectasia. CCC alters the corneal structure and biomechanics. The induced increase in corneal rigidity may interfere with accurate measurement of intraocular pressure (IOP). To investigate the effects of CCC on IOP measurements obtained by different tonometers, we compared IOP readings before and after CCC using Goldmann Applanation Tonometry (GAT), Dynamic Contour Tonometry (DCT) and the TonoPen XL® (TP) in an in vitro model.
10 human eye bank corneas considered unsuitable for transplantation were de-epithelialized and mounted on an artificial anterior chamber. The hydrostatically controlled pressure in the chamber was adjusted from 10 to 40 mmHg in 5 mmHg steps. IOP was measured by GAT, DCT and TP before and after CCC, which was performed using a 0.1% riboflavin solution and 30 minute UVA irradiation.
Before CCC the manometric reference pressure showed an excellent concordance with GAT and DCT readings but was overestimated by TP. After CCC all tonometers showed higher readings. The mean deviation between IOP readings after and before CCC was +1.6 (± 3.6 SD) mmHg for DCT, +3.0 (± 6.6) mmHg for GAT and 3.2 (± 8.8) mmHg for TP.
In this in vitro model on normal de-epithelialized human corneas CCC resulted in an overestimation of IOP as compared to the reference pressure. The magnitude of this effect differs between the tonometry principles tested. For DCT and GAT the magnitude is too small to create a serious clinical safety problem for patients undergoing this novel treatment.
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