Aim: This study was undertaken to compare the measurement of intraocular pressure (IOP) in a population-based glaucoma survey by the Goldmann Applanation Tonometer (GAT) and the Tonopen with respect to IOP readings, the time required to measure IOP and subjects' preference for the two instruments. The purpose of the study was to see which of the two instruments could be more suitable in a rural survey, particularly house-to-house, in trying to find cases of advanced glaucoma.
Method: The study was conducted on a total of 203 subjects as a part of a population-based glaucoma survey. The IOP of one randomly selected eye of each subject was measured, first with the GAT and subsequently with the Tonopen. The time taken for each procedure was noted and subjects' preference was ascertained.
Results: The mean of the paired differences between the readings of the two instruments (Tonopen minus GAT) was 1 mm Hg with a standard deviation of 2.28. The Tonopen readings were within +/-3 mm Hg of the GAT readings in 86.2% of eyes. In 7.4% of the eyes the paired differences were > or =+/-5 mm Hg. Measurement of IOP by the Tonopen was much quicker, the mean time difference being 38.7 sec. Subjects' preference for the Tonopen was higher.
Conclusion: The overall agreement between the measurements of the two instruments was good but a small percentage of large difference (> or = +/-5 mm Hg in 7.4%) may be of concern in a population-based survey. The time to measure IOP and the subjects' preference were strongly in favour of the Tonopen.