Tono-Pen tonometer and corneal thickness.

Objective: To compare the intraocular pressure (IOP) measurements taken at the central cornea with those taken at the mid-peripheral cornea using the Tono-Pen tonometer.

Methods: Forty-eight normal human subjects had their IOP measurements taken (i) with the Goldmann tonometer, (ii) with the Tono-Pen at the central cornea and (iii) with the Tono-Pen at the mid-peripheral cornea. The central and mid-peripheral corneal thickness at the site of IOP measurements were then determined by ultrasonic pachymetry.

Results: The mean IOP with the Goldmann tonometer was 15.7 +/- 3.1 mmHg. The mean Tono-Pen IOPs at the central and midperipheral cornea were 15.2 +/- 3.2 mmHg and 15.7 +/- 3.3 mmHg respectively. The mean midperipheral corneal thickness (578 microns) was significantly higher than the mean central thickness (538 microns) (p < 0.001).

Conclusions: There was no significant difference between the IOP taken with the Tono-Pen and with the Goldmann tonometer. In addition, no clinically significant difference was observed between the IOP readings of central and mid-peripheral cornea measured by the Tono-Pen.