[Transpalpebral tonometry with a digital tonometer in healthy eyes and after penetrating keratoplasty]

Abstract

Purpose: The Goldmann applanation technique established itself as gold standard for clinical intraocular pressure (IOP) measurement. But the device measures by corneal touch and presupposes corneal conditions within a normal range. So precise determination of IOP is crucial in corneal disorders and after corneal surgery. This pilot study presents tonometry data of normal and postkeratoplasty eyes measured transpalpebrally with a digital tonometer in comparison to Goldmann tonometry.

Method: The TGDc-01 tonometer is based on a ballistic principle of measurement. IOP was measured in 50 healthy eyes (group 1) and 40 eyes after penetrating keratoplasty (group 2) first by the TGDc-01 and after 3 minutes by Goldmann tonometry (Haag-Streit). Subjective refraction, keratometry and ultrasonic pachymetry were performed in all eyes. The IOP measurements in the postkeratoplasty eyes were done when corneal epithelium was fully closed and only a medium suture edema could be observed.

Results: The Pearson's product-moment correlation was r=0,46 for group 1 and 0,65 for group 2. Using the concordance correlation coefficient the value showed a reproducibility index of r(c)=0,44 in group 1 and r(c)=0,60 in group 2. Following the Bland-Altman-analysis 58% of the cases in group 1 had a difference between the two instruments of maximum 3 mmHg. In group 2, 53,5% of the eyes showed an absolute difference between Goldmann and TDGc-01 of 3 mmHg or less.

Conclusion: A transpalpebral measurement technique-avoiding corneal contact-seems to be an alternative choice in patients with corneal pathologies and after corneal surgery. The TGDc-01 tonometer provided mostly similar results compared to the Goldmann device, but with fluctuations. Keeping the deviations between the two methods in mind we recommend, however, the use of the transpalpebral approach only in combination with other techniques (palpation, indentation) to obtain enough reliability of IOP information in problem eyes.