Reliability of proton and goldmann applanation tonometers in normal and postkeratoplasty eyes

To compare the reliability of intraocular pressure (IOP) measurements with the ProTon tonometer and the Goldmann applanation tonometer (GAT) in normal and post-penetrating keratoplasty (post-PK) eyes.

Prospective, nonrandomized, comparative case series.

Twenty-four individuals (48 eyes) with no known ocular disorder and 59 patients (59 eyes) that had undergone penetrating keratoplasty (PK) were included in the normal and post-PK groups, respectively.

Three readings at 5-minute intervals each were obtained with GAT and ProTon in both the groups. Each reading with ProTon was a mean of five accepted readings with the highest accuracy (standard error of mean, <0.5 mmHg). In post-PK eyes with more than 3.00 diopters of astigmatism or with irregular astigmatism, the mean of two readings taken with GAT in the steepest and flattest axis was considered to be the IOP.

The IOP measurements in all groups were compared using a two-tail paired t test. The coefficient of repeatability and Cronbach's coefficient alpha were calculated separately for the IOP measured using both instruments in each group.

There was no significant difference in the second (r1) and third (r2) IOP reading using the GAT and ProTon tonometers in normal and post-PK eyes. The coefficients of repeatability for GAT and ProTon were 2.64 and 2.49 in normal versus 3.72 and 3.47 in the post-PK group. The Cronbach's alpha for GAT and ProTon was 0.94 and 0.95 in the normal group versus 0.95 for both GAT and ProTon in the post-PK group.

The results of our study show that the ProTon tonometer is reliable and comparable with GAT for recording IOP in normal and post-PK eyes.