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Effect of Riboflavin-UVA–Induced Collagen Cross-linking on Intraocular Pressure Measurement

¹From the Department of Ophthalmology and the ²Horten Centre for Patient-Oriented Research, University of Zurich, Zurich, Switzerland; the ³IROC Institute for Refractive and Ophthalmic Surgery, Zurich, Switzerland; and the ⁴Department of Ophthalmology, Cantonal Hospital Lucerne, Lucerne, Switzerland.

PURPOSE. Corneal collagen cross-linking (CCL) with riboflavin and ultraviolet A irradiation has recently been introduced for treatment of corneal ectasia. Yet a CCL-induced increase in corneal rigidity may interfere with intraocular pressure (IOP) measurements. In an investigation of the effect of CCL on the accuracy of IOP measurements, IOP readings before and after CCL were compared.

METHODS. Ten human eye bank corneas were de-epithelialized and mounted on an artificial anterior chamber. The hydrostatically controlled reference pressure in the chamber was adjusted from 10 to 40 mm Hg in 5-mm Hg steps. IOP was measured by Goldmann applanation tonometry (GAT; Haag Streit, Könitz, Switzerland), dynamic contour tonometry (DCT; Pascal tonometer; Ziemer Ophthalmics, Port, Switzerland), and the TonoPen XL (TP; Tono-Pen XL, Medtronic, Jacksonville, FL) before and after CCL, which was performed with a 0.1% riboflavin solution and 30 minutes of UVA irradiation.

RESULTS. Before CCL, GAT, and DCT readings showed an excellent concordance with the manometric reference pressure, whereas TP overestimated the true IOP. After CCL, the reliability of IOP readings decreased with all three tonometers. This decrease resulted in a slight overestimation of mean IOP, but there were also some potentially dangerous underestimations in some individual corneas. The mean (±SD) difference between IOP readings after and before CCL was +1.8 (3.5) mm Hg for DCT, +2.9 (6.1) mm Hg for GAT, and +3.1 (8.3) mm Hg for TP (P 0.002 for DCT versus GAT or TP).

CONCLUSIONS. In this in vitro model on human corneas, CCL resulted in an overestimation of true IOP by all the tested tonometers. Although the magnitude of this effect was small, care should be taken when measuring IOP with GAT after CCL, as it results in less accurate, much more variable IOP readings.