The Measurement of Intraocular Pressure in Eyes with Keratoconus Using Pascal Dynamic Contour Tonometer

Purpose: To compare Pascal dynamic contour tonometer (DCT) with other tonometric systems for measurement of intraocular pressure (IOP) in eyes with keratoconus which has thinned cornea and topographically indicated keratoconus pattern and to investigate whether central corneal thickness (CCT) affect IOP measurements or not. Material and Method: Our study included 44 eyes of 28 patients which were diagnosed as keratoconus clinically and topographically. Their central corneal thicknesses which were measured with ultrasonographic pachymeter were under 500 microns (mu). IOP's were estimated using Pascal DCT, Goldmann applanation tonometer (GAT) and non contact air-puff tonometer (NCT). The "mean" IOP accepted as the mean of three consecutive measurements in different times. The "mean" IOP's values using Pascal DCT, GAT and NCT compared with paired student t test with each other. Statistically significance limit was p< 0,05. Pearson correlation analysis was used to determine the effect of CCT on IOP. Correlation coefficient was accepted r> 0,25 (p< 0,05). Results: The mean age of 28 patients with keratoconus was 30,18 +/- 8.8 years. In 44 study eyes, the mean value of CCT's was 465,8 +/- 24,1 mu. The mean values of IOP's using Pascal DCT, GAT and NCT were 14,3 +/- 2,3 mmHg, 11,1 +/- 2,6 mmHg, 8,11 +/- 1,9 mmHg, respectively. The mean IOP using Pascal DCT was statistically higher than the mean values of GAT and NCT (Student t test; p< 0,05). IOP measured with NCT were significantly correlated with CCT (Pearson correlation analysis r1= 0,26, p< 0,05) but IOP measured with GAT and Pascal DCT were not effected (for GAT r(2)= 0,09; for DKT r3= 0,06, p> 0,05). Conclusion: In eyes with keratoconus, the highest IOP value was measured with Pascal DCT. The measured IOP's using NCT was affected by the changes in CCT but the IOP's measured with Pascal DCT and GAT were not. When the technical problems with using GAT in eyes with keratoconus which was thinned and topographically distrurbed cornea are considered, we thought that to use Pascal DCT is more accurate and safely.