Abstract
Purpose: :
To evaluate the diurnal variation of intraocular pressure (IOP) measurements obtained by Goldmann applanation tonometry (GAT), Pascal dynamic contour tonometry (PDCT), and non-contact tonometry (NCT) and to study their relationship to central corneal thickness (CCT) in non-glaucomatous eyes.
Methods: :
This is a prospective study of 38 eyes from 38 non-glaucomatous subjects who underwent intraocular pressure (IOP) measurements by GAT, PDCT and NCT. IOP was measured during office hours, at 08:00 am, 12:00am, 04:00 pm and 08:00 pm. Two consecutive GAT followed by three consecutive PDCT and three NCT IOP measurements were taken in each session by the same investigator. Only PDCT measurements with quality 1 and 2 were taken into account. CCT was obtained by ultrasound pachymeter after the last IOP measurement. The effect of CCT was correlated with the GAT/P DCT/ NCT IOP differences as well as with diurnal IOP and ocular pulse amplitude (OPA) variation.
Results: :
Mean age was 28.2±7.4 years. Mean PDCT values were significantly higher than GAT (mean 15.6 ± 3.0 mmHg vs. 14.1 ± 3.7 mmHg, p:0.0005) and NCT readings (mean 15.6 ± 3.0 mmHg vs. 14.0 ± 4.0 mmHg, p:0.0001). The mean OPA was 1.9 ± 0.9 mmHg (range 0.8-3.5 mmHg). The mean amplitude of diurnal OPA variation was 0.39 ± 0.26 mmHg. No significant changes were observed in GAT, PDCT and NCT IOP measurements during office hours (ANOVA; GAT: F= 0.2, P = 0.87; DCT: F = 0.14, P = 0.93; NCT: F =0.03; P = 0.99). Diurnal IOP variation with GAT was 1.9 ± 1.1 mmHg, with PDCT was 2.1 ± 1.3 mmHg and with NCT was 2.1 ± 1.0 mmHg. The difference among the IOP diurnal variations obtained by the three devices was not statistically significant (p>0.05). CCT was significantly correlated with GAT and NCT IOP. CCT was correlated only with PDCT IOP diurnal variation (Spearman’s r=0.45, P=0.004) and not with GAT and NCT variation (r=0.15, P=0.36 and r=-0.07, P=0.67, respectively). The differences in IOP measurements (GAT-PDCT, GAT-NCT, PDCT-NCT) were significantly correlated with CCT. CCT was not correlated with PDCT IOP readings, OPA readings and OPA diurnal variation.
Conclusions: :
In non-glaucomatous eyes, mean PDCT IOP values were significantly higher than mean GAT and NCT IOP values. There were no statistically significant differences among the diurnal IOP variation measurements obtained by GAT, PDCT and NCT. IOP, measured with GAT and NCT, varied independently of CCT. However, CCT was correlated with DCT IOP diurnal variation.
Keywords: intraocular pressure • intraocular pressure • intraocular pressure