Improved illumination for the Perkins applanation tonometer.

Abstract

To improve the Perkins tonometer measurements by using an augmented, monochromatic solid-state light source of 470 nm wavelength. This prospective study comprised 44 patients of our ophthalmic department who were split into two groups of 21 and 23 patients, and were tested by two independent ophthalmologists. Intraocular pressure (IOP) was measured in both eyes, comparing the instrument with augmented source against the standard Perkins for both observers. A set of three consecutive IOP measurements was recorded on each patient's eye and the time required to make each of them was recorded. The mean of the three IOP values was used in the analyses. For Observer 1, higher values of IOP with our augmented illumination against the standard were recorded, the mean difference of +0.59 mmHg being statistically significant (95% CI, 0.0 to +1.18 mmHg). For Observer 2, the mean difference of -0.22 mmHg was not significant (95% CI, -0.70 to +0.26 mmHg). Measurement times for observers were shorter when using the augmented illumination (Observer 1: mean difference = -2.0 s, S.E. = 1.4 s, CI, +0.8 to -4.9 s; Observer 2: mean difference = -5.0 s, S.E. = 1.3 s, CI, -2.5 to -7.5 s). The monochromatic blue light source may improve the performance of IOP measurements with the Perkins instrument under bright room conditions, making them faster and more convenient.