Hand-held dynamic contour tonometry.

PURPOSE: We present a prototype of the hand-held dynamic contour tonometer (HH-DCT) and prospectively compare this HH-DCT with the well-established Perkins applanation tonometer (PAT) and the TonoPenXL (TPXL). METHODS: In a prospective, single-centre, randomized study, intraocular pressure (IOP) readings were taken in random order using HH-DCT, PAT and TPXL tonometers. Intra-observer variability was calculated for each observer and compared between three experienced ophthalmologists and an inexperienced medical student. RESULTS: Ninety-two corneas of 92 healthy participants were enrolled. IOP [mean mmHg ± standard deviation (SD)] as measured by HH-DCT was 16.97 ± 2.71, by PAT 13.98 ± 2.52 and by TPXL 13.34 ± 2.68. The range of three consecutive IOP readings differed significantly between the devices [p < 0.001; mean range: 1.45 ± 1.07 (HH-DCT), 1.87 ± 0.97 (PAT) and 2.08 ± 1.77 (TPXL)]. There was no difference of the range in all devices between the ophthalmologists and the medical student (HH-DCT p = 0.68, PAT p = 0.54, TPXL p = 0.48). CONCLUSION: IOP readings measured by HH-DCT are significantly higher than by PAT and TPXL. The differences of IOP measurements are in good accordance with previous studies using the slit-lamp-mounted DCT (SL-DCT) and Goldmann Applanation Tonometry, where SL-DCT readings were 1-3.2 mmHg higher. HH-DCT seems to give more constant results, which can be seen in the lower intra-observer variability compared to PAT and TPXL.

Effect of riboflavin-UVA-induced collagen cross-linking on intraocular pressure measurement.

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