Comparing the Tonojet disposable tonometer with the traditional Goldmann tonometer in glaucomatous and non-glaucomatous eyes.

Applanation tonometry is widely performed as the most accurate method of measuring intraocular pressure in the clinical setting. Disposable tonometer heads reduce the risk of transmitting infection during applanation and eliminate tonometer head cleaning, which is time-consuming. We performed a study to investigate whether the Tonojet disposable tonometer (Luneau, France) gave comparable intraocular pressure measurements to the standard Goldmann tonometer produced by Haag Streit (Switzerland). The study was performed in a busy general secondary referral ophthalmology clinic in Beaumont Hospital over a 15-day period. We measured intraocular pressure with the Goldmann and Tonojet tonometers in 293 eyes. Patients were randomised as to which tonometer was used first. A diagnosis of glaucoma or ocular hypertension was noted. Central corneal thickness (CCT) was measured. The measurements taken with the Tonojet were on average 2.2 mmHg lower than corresponding measurements taken with the Goldmann applanation tonometer head. The bias was present over the entire range of pressures. The 95 % limits of agreement between the two tonometers ranged from -5.9 to +1.4 mmHg. In the cohort of eyes with ocular hypertension/glaucoma the difference was significantly higher (2.8 vs. 2.1 mmHg). The bias was independent of CCT. We found that the Tonojet disposable tonometer tends to underestimate intraocular pressure compared with the Goldmann. The bias is non-systematic, present over the entire range of pressures and independent of corneal thickness. We conclude that the Tonojet is not sufficiently accurate to constitute a suitable alternative to the Goldmann.