Background: Recent comparisons between transpalpebral tonometry using TGDc-01 and Goldmann applanation tonometry were performed in populations with IOPs between 10 and 20 mmHg. The purpose of this study was to evaluate device deviations depending on different IOP levels (range 5-40 mmHg).
Methods: A total of 68 eyes of 68 patients were included and assigned to four IOP levels according to an initial applanation tonometry assessment: level I, <10 mmHg (n=8); level II, 10-19 mmHg (n=20); level III, 20-29 mmHg (n=20); and level IV, > or =30 mmHg (n=20). Two independent and randomized observers performed three replicate measurements per eye-observer 1 using TGDc-01 tonometry, and observer 2 using Goldmann applanation tonometry. Intraindividual deviations between measurement results were investigated concerning clinical relevance by medians and quartiles, concerning statistical significance by pairwise sign tests; p values <0.05 indicate local statistical significance.
Results: In patients with initial IOP > or =20 mmHg, TGDc-01-based tonometry significantly underestimated the IOP as based on Goldmann applanation tonometry (p<0.001). This effect increased with increasing IOP: IOP level III median difference (TGDc-01 - Goldmann) -1.3 mmHg (interquartile range, -2.5, -0.4), IOP level IV median difference -2.7 mmHg (-3.7, -1.0). In patients with initial IOP <10 mmHg, an at least gradual underestimation by TGDc-01 tonometry (p=0.219; median difference, -0.6, -1.6, 0) was observed. A total 18% of patients showed device deviations > +/-3 mmHg, and even 35% of those patients with initial IOP > or =30 mmHg.
Conclusions: TGDc-01-based tonometry demonstrated an increasing underestimation of IOP with increasing IOP levels when compared with the current standard method of Goldmann applanation tonometry.