Abstract
Purpose: :
This study compares intraocular pressure (IOP) measurements obtained using the Goldmann applanation tonometer (GAT) to four other tonometers, Reichert pneumatonometer (RPT), Tonopen, Pascal dynamic contour tonometer (PDCT), and Schiotz tonometer (Schiotz). The effect of age and central corneal thickness (CCT) on the measurement discrepancy between GAT and other tonometers was evaluated.
Methods: :
Enrolled were 159 subjects between the ages of 21 and 84 years with normal IOPs, or with ocular hypertension or glaucoma. IOP by each tonometer was measured sequentially with ICare, PDCT, GAT, Tonopen, RPT, Schiotz tonometer, and OBT in this order. CCT was measured by ultrasound pachymetry either before or after all the IOP measurements were obtained.
Results: :
There was a positive linear correlation between CCT and IOP measurements with all tonometers (p<0.04). The magnitude of the correlation was highest for Schiotz (R2 =0.15, p<0.0001). A statistically significant positive linear correlation was detected between age and IOP when using GAT (R2 =0.15, p<0.0001), Tonopen (R2 =0.03, p=0.04), PDCT (R2=0.08, p=0.0002) and RPT (R2=0.04, p=0.01). Overall, GAT IOPs were significantly lower than IOPs obtained using PDCT and RPT (T-test p<0.0001).The difference in measurements between GAT and RPT, PDCT or Schiotz was significantly greater in subjects under 40 than over 40 years of age (t-test p<0.01). Tonopen IOPs were overall higher than GAT in subjects under 40 and lower than GAT in subjects over 40 with the difference between the 2 groups being statistically significant (p=0.002). The difference between IOP by GAT and IOP by any of the other tonometers was positively linearly correlated with age (p<0.05).
Conclusions: :
This study shows that IOP measured by GAT is positively correlated with CCT and age. GAT provides lower IOP measurements compared to PDCT and RPT. The differences between GAT IOPs and IOPs by the other tonometers are significantly affected by age. The largest differences between GAT and other tonometers are found in younger subjects. Understanding the IOP differences by different tonometers is important in clinical care.
Clinical Trial: :
University of Nebraska, NCT00570791
Keywords: intraocular pressure • aging