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A new tonometer--the pressure phosphene tonometer: clinical comparison with Goldman tonometry
Objective:
This study aimed to compare the results of pressure phosphene tonometry, a new tonometric technique, with Goldmann applanation tonometry.
Design:
Comparative case series.
Participants:
A total of 100 consecutive patients (192 eyes) without diagnostic specificity, plus a separate subset of 14 eyes with intraocular pressure (IOP) above 19 mmHg, participated.
Intervention:
Intraocular pressure was measured with Goldmann tonometry by one examiner and pressure phosphene tonometry by a different examiner. There was no communication between the examiners regarding test results.
Main Outcome Measures:
Intraocular pressure.
Results:
In the group without diagnostic specificity, the mean difference between the two techniques was 0.3 mmHg. Fifty-one percent of the measurements were within +/-1 mmHg, 74.9% of the measurements were within +/-2 mmHg of each other, and the average deviation for 100% of the data was 1.8 mmHg. For pressure phosphene tonometry, the mean IOP was 15.2 mmHg with a standard deviation of 2.9 and a range of 18 mmHg (minimum, 10; maximum, 28). With Goldmann, the mean was 15.5 mmHg, the standard deviation was 3.1, and the range was 20 mmHg (minimum, 8; maximum, 28). The t test for paired data showed a Gaussian approximation with a P value of 0.05. A comparison between the results of the two techniques gave a correlation coefficient of 0.71. Results for the separate 14 patients with higher IOPs yielded a statistically significant mean difference of 0.1 mmHg between the two techniques (P < 0.05, t test for paired data). For pressure phosphene, the mean was 21 mmHg with a standard deviation of 5.5 and a range of 24 mmHg (minimum, 14; maximum, 38). For Goldmann, the mean was 21.1 mmHg with a standard deviation of 4.7 and a range of 19 mmHg (minimum, 15; maximum, 34). The correlation coefficient was 0.73.
Conclusions:
The close agreement between the two techniques suggests that pressure phosphene tonometry offers an alternative method for measuring IOP. It has the advantages that it is simple, noninvasive, and inexpensive. Potential uses of the pressure phosphene tonometer may include self-administered home testing, in outreach clinics by nonophthalmic technicians, and in patients with corneal conditions that preclude the use of Goldmann tonometry.