Clinical comparison of the ocular blood flow tonograph and the Goldmann applanation tonometer

Purpose. To compare the IOP readings of an ocular blood flow (OBF) tonograph (OBF Labs UK Ltd) with Goldmann applanation tonometry. Methods. 194 patients were studied. In group 1, the software version 8.2 of the OBF tonograph was used in 214 eyes of 107 patients and in group 2, the 11.2 version of the tonograph was used in 174 eyes of 87 patients. Results. We found 63% of the OBF tonograph readings to be within +/-2 mm Hg of the Goldmann applanation tonometry readings in group 1 and 60% in group 2. In group I the correlation coefficient between the readings of the two instruments was 0.71 and 0.82 in group 2. The mean value for the paired differences in group 1 was -1.34+/-2.75 mm Hg overall and -1.04+/-2.91 mm Hg overall in group 2. There was a significant difference between the Goldmann applanation tonometer and OBF tonograph readings in the 8-10 mm Hg interval (p<0.001) in group I, but not in group 2 (p>0.1). Conclusions. The 11.2 version of the OBF tonograph is more accurate than the 8.2 version and measures IOP in a manner that corresponds well to the Goldmann applanation tonometer in the 8-10 mm Hg and 21-29 mm Hg intervals. It corresponds fairly well in the 11-20 mm Hg interval.