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Reliable measurements of the intraocular pressure (IOP) are necessary for glaucoma patients. The measuring procedure, anatomical changes of the eye or extraocular influences can lead to errors during applanation tonometry. The IOP is overestimated if measured through the wrong eyepiece of the slit lamp, if a force is interfering with the tonometer arm during the measurement, if the lid comes into contact with the tonometer tip, if blepharospasm occurs, if there is lid retraction or if a Valsalva maneuver is present. An underestimation of the IOP occurs if staining with fluorescein is absent or insufficient, if the illumination is not bright enough, if a corneal stromal edema is present, after LASIK, during accommodation, during repeated measures within a few minutes or during systemic blood pressure drop. Discrepancies of the IOP in both directions can appear if the calibration of the tonometer is irregular, if abnormal central corneal thickness or astigmatism is present. For correct measurements calibrations are advised once or twice a year.

Purpose: To assess acute corneal decompensation after silicone oil removal in some aphakic eyes with clear corneas whose anterior chambers were completely filled with silicone oil for a considerable period of time. Methods: Eight eyes of 8 patients who underwent vitrectomy and intraocular silicone oil injection were studied. All the eyes were aphakic and anterior chambers were completely filled with silicone oil. In all eyes, corneas were clear and no corneal finding indicating keratopathy was detected by slit-lamp microscopy before silicone oil removal. The mean silicone oil removal time was 4 months (range 2–7 months). A specular microscope was used for the evaluation of corneal endothelial changes and corneal pachometry was performed to observe corneal changes before and after the silicone oil removal in 5 eyes besides slit-lamp microscopy. The follow up period after silicone oil removal was 2–12 months (mean 6 months).Results: In all eyes severe corneal stromal edema and clouding was detected in the first day following silicone oil removal. Increased corneal thickness was seen in all eyes. Decreased (at or below critical levels) corneal cell density was detected by specular microscopy before and after silicone oil removal. No significant improvement was observed during the follow up period. Conclusion: Eyes whose anterior chambers completely filled with silicone oil could be evaluated as clear corneas by slit lamp microscopy despite severe endothelial damage. We recommend that eyes with silicone oil in the anterior chambers should be monitored by a combination of slit-lamp microscopic examination and specular microscopy to determine the relative corneal endothelial tolerance to the silicone oil and endothelial damage. Early removal of the silicone oil can be considered when the retinal adhesion allows.