Assessment of a new Goldmann applanation tonometer

Even-number measurement bias with Goldmann applanation tonometry in patients with glaucoma and glaucoma suspects

CLINICAL RELEVANCE

Goldmann applanation tonometry is widely used for the diagnosis and management of glaucoma and its use is considered standard of care. However, the precision of this method may be reduced by a clinician tendency to round to even numbers.

BACKGROUND

Studies have previously demonstrated an even-number measurement bias with Goldmann applanation tonometry during examination of a general patient population. Since it has not been determined whether this bias persists among glaucoma suspects and patients with glaucoma, further investigation was conducted.

METHODS

A retrospective analysis was conducted on a random sample from a large dataset of >69,000 patients seen during a six-year period at an urban, academic primary eye care service. Patients without suspicion of glaucoma, patients with a suspicion of glaucoma, and patients with glaucoma were selected who had Goldmann tonometry performed. Chart reviews were performed to confirm status, and even/odd-numbered Goldmann tonometry measurement frequencies were compared.

RESULTS

The analysis included 961 controls, 506 glaucoma suspects, 159 ocular hypertensives not taking medication, and 314 patients taking medications who carried a diagnosis of glaucoma or ocular hypertension. Among controls the Goldmann tonometry even/odd digit proportions were 62.8%/37.2% (N = 961, p < 0.0001), and the even-number bias persisted among the other groups with specific even/odd distributions being 61.9%/38.1% (N = 506, p < 0.0001) for glaucoma suspects not taking medications, 66.0%/34.0% (N = 159, p < 0.0001) for ocular hypertensives not taking medications, and 64.3%/35.7% (N = 314, p < 0.0001) for glaucoma/ocular hypertension patients taking medications.

CONCLUSION

An even-number measurement bias with Goldmann tonometry may be prevalent even when the examiner is aware of there being greater importance for intraocular pressure measurement accuracy.

Evaluation of the New Digital Goldmann Applanation Tonometer for Measuring Intraocular Pressure

Purpose. To compare a new digital Goldmann applanation tonometer (dGAT) that measures intraocular pressure (IOP) in 0.1 mmHg increments to a standard Goldmann applanation tonometer (sGAT).Methods. This study included 116 eyes of 60 subjects. A single examiner first measured IOP in triplicate using either sGAT or dGAT, which was randomly chosen. After a 5-minute interval, the next set of three consecutive IOP was measured using the other GAT.Results. The mean IOP measured with sGAT was 16.27 ± 6.68 mmHg and 16.35 ± 6.69 mmHg with dGAT. Pearson’s correlation coefficient was 0.998 (P<0.01). The subjects were divided into three groups based on the mean IOP: IOP < 14 mmHg, 14–20 mmHg, or >20 mmHg. The Pearson’s correlation coefficient within each group was 0.935, 0.972, and 0.997 (P<0.01), respectively. The difference within the three consecutive IOP measurements (maximum–minimum) for dGAT (0.72 ± 0.34 mmHg) was significantly smaller than those with sGAT (0.92 ± 0.42 mmHg,P<0.01). Even in patients with equal IOP (zero left-right difference) with sGAT (n=30), dGAT detected IOP differences between the left and right eyes (0.47 ± 0.31 mmHg).Conclusion. Compared to sGAT, dGAT measurements are highly reproducible and less variable.