Comparison of Luneau SA disposable and Goldmann applanation tonometer readings

Abstract

Purpose To test the agreement of intraocular pressure (IOP) measurements made with Luneau SA applanators and Goldmann applanator. Materials and Methods A single-blind crossover trial. IOPs were measured in both eyes of subjects with both applanators. Type of applanator was alternated to eliminate systematic bias. Multiple observers were used. Observers were blind to the scale while performing measurements but not to the type of applanator used. The appearance of the meniscus was assessed semiquantitatively. All measurements were combined and presented in a Bland-Altman plot. Results A total of 140 eyes of 79 subjects were tested by seven observers. The range of measurements was 6-45 mmHg (mean 17.8 mmHg) for the Goldmann applanator. On average, the Luneau SA applanator (range of measurements 4-36 mmHg) gave a measurement of 2.35 mmHg less than the Goldmann standard. The standard deviation of these differences was 2.13 mmHg, giving an upper 95% confidence limit of 6.53 mmHg and a lower 95% confidence limit of À1.83 mmHg. The measurements agreed in only 24 out of 140 instances. In 28 eyes, the disposable tonometer end point was difficult to assess owing to excessively thick rings. Linear extrapolation suggests an increase in difference with increasing IOP. Conclusion The inter-head inaccuracy, tendency to underestimate IOP, and lack of systematic inaccuracy make a corrective algorithm impossible to formulate. The range of variation between the Luneau SA disposable applanator and the Goldmann standard is sufficiently large to influence clinical management decisions. We speculate that one explanation is the interaction of the tonometer with the tear film, making end point determination difficult. Further research is being undertaken.

Does the surface property of a disposable applanation tonometer account for its underestimation of intraocular pressure when compared with the Goldmann tonometer?

“…Our experiments showed that the suction forces for the two tonometers were equivalent to 0.26 and 0.19 mmHg; these values were at least one order of magnitude smaller than the differences observed clinically. Additionally, when we compared the IOP of the Goldmann and Tonojet using Bland Altman plots, we did not find a consistent underestimation by a fixed amount, which one might have expected if the suction force was solely responsible for the difference in IOP measurements [1].…”

“…The tonometer is extracted past the surface of the liquid at position (d) and as it draws up a column of liquid. The force increases steadily to overcome the suction force until (e) when the column collapses and the force returns to zero at (f) 1 This is a 2% sodium hypochlorite solution. The active ingredients include sodium hypochlorite 2% w/w and sodium chloride 16.5% w/w.…”

“…The standard deviation of these differences was 2.13 mmHg, giving an upper 95% confidence limit of 6.53 mmHg and a lower 95% confidence limit of −1.83 mmHg [1].…”

How should we measure intraocular pressure in the era of coronavirus disease 2019? Balancing infectious risk, cleaning requirements, and accuracy

“…In their study, they inspected the prisms prior to use and found that 14 of 189 disposable tips had to be discarded because of the presence of surface irregularities. Baddon et al [ 33 ] found that in 28 of the 140 eyes included in the study, the tonometer endpoint was difficult to assess with Luneau prisms because of excessively thick rings. The menisci endpoint was deemed to be of acceptable quality in 80% of the Luneau tip readings and 100% of the GAT readings.…”

“…range of 0.1-0.5 mmHg [26][27][28][29][30][31]. Studies comparing the Luneau Tonojet to reusable tip GAT found a mean IOP difference of 0.4-2.35 mmHg [26,32,33].…”