Tono-Pen tonometry in normal and in post-keratoplasty eyes.

Abstract

Oculab Tono-Pen tonometry was compared with Goldmann applanation tonometry in 82 eyes of 82 patients with normal corneas and in 54 eyes of 54 patients who had undergone penetrating keratoplasty and whose corneas did not preclude the use of the Goldmann tonometer. We found that the intraocular pressure (IOP) This instrument has certain advantages over the Goldmann applanation tonometer. It is portable and compact, can be used regardless of the patient position, is easy to calibrate and operate, has a disposal tip cover which eliminates contamination risks, and the digital readout minimises user bias. Because of its small contact diameter (1I5 mm) the Tono-Pen was recommended for the measurement of the IOP in eyes with irregular corneas. ' Our goal was to try to find if the IOP differences between Tono-Pen and Goldmann in normal eyes would be similar in post-keratoplasty eyes which often have large and irregular astigmatism. In addition, we wanted to find a correction factor for the Tono-Pen which could be used to make it clinically comparable with the Goldmann tonometer. Figure 1 shows the regression line of the TonoPen IOPs compared with Goldmann IOPs (y= 0 87,x+5 63, correlation coefficient 0-83) in eyes with regular corneas. Table 1 compares the measurements of both tonometers, in terms of mean paried differences and mean absolute value of paired differences in normal eyes. The analysis is divided into several Goldmann tonometry based IOP intervals. There were significant differences between the two instruments (-3 59 (SD 0 36) mm Hg, p<0-oo0l). Figure 2 displays the distribution of paired IOP differences in the group of normal eyes. Most of the measurements are situated left of the zero, representing overestimation of the TonoPen; only 52% of the Tono-Pen measurements 538 on 11 May 2018 by guest. Protected by copyright.

Graft failure: III. Glaucoma escalation after penetrating keratoplasty

“…When the Tono-pen was compared with the MacKay-Marg tonometer, there was no significant difference in IOP measurement in normal corneas and in corneas after PKP and epikeratophakia [87]. However, Geyer et al found the Tono-pen to overestimate compared with the Goldmann tonometry readings in both normal and post-keratoplasty eyes, especially in the lower IOP range (\9 mmHg) [88]. Another electronic portable tonometer similar to the Tono-pen is the ProTon tonometer.…”

Comparative evaluation of TonoPen AVIA, Goldmann applanation tonometry and non-contact tonometry

“…Several authors have demonstrated that the TonoPen XL tends to overestimate low IOPs and underestimate high IOPs [12][13][14], while others have concluded that there is no such variation [15,16].…”

Comparison of Different Methods for Measurement of Intraocular Pressure and Evaluation of Effect of Central Corneal Thickness on Measurement Results

“…Literatürde farkl› ölçüm yöntemlerini karfl›laflt›ran birçok çal›flma mevcuttur. Bu öl-çüm yöntemlerinden tonopen ve GAT ile ölçümler aras›n-da uyum oldu¤unu bildiren çal›flmalar (12)(13)(14)(15) (16)(17)(18)(19)(20). Bir çal›flmada tonopen ve GAT ile elde edilen ölçümler aras›nda 20 mmHg'nin alt› için iyi bir uyum oldu¤u ancak 20 mmHg'nin üstündeki bas›nçlar için tonopenin anlaml› olarak daha düflük ölçüm yapma e¤ilimi gösterdi¤i bildirilmifl ve tonopenin güveni-lirli¤inin GAT ile karfl›laflt›r›labilir oldu¤u savunulmufltur (12).…”