TonoPen, Pascal Dynamic Contour tonometer suitable in PK eyes

This study compared IOP measurements taken using four different methods in eyes that had undergone penetrating keratoplasty (PK). The results indicate that TonoPen XL or Pascal Dynamic Contour tonometer (PDCT) are the most suitable alternatives for measuring IOP in eyes that have undergone PK in which Goldmann applanation tonometry (GAT) readings are difficult to obtain.

The authors note that the gold standard for IOP measurement, GAT, has limitations in corneas that deviate significantly from normal values, as is the case in PK eyes. The study's results also indicate that PDCT results were independent of both central corneal thickness (CCT) and corneal astigmatism measurements at all postoperative stages.

Thirty-one subjects (31 eyes) were included in this prospective study. IOP measurements were taken in these eyes using GAT, TonoPen, PDCT and Ocular Response Analyzer (ORA) a mean of 27.7 months after PK. The authors assessed CCT and corneal astigmatism by Pentacam rotating Scheimpflug Tomography. These results were correlated with the IOP readings.

They found that IOP measured with GAT and TonoPen was similar. Although there was an extremely strong correlation between PDCT and GAT measurements (P = < 0.01), IOP measured with both PDCT (2.12 mmHg, P < 0.01) and ORA (6.29 mmHg, P < 0.01) was significantly higher than with GAT. They say these data suggest that ORA is the least useful measure of IOP in eyes that have undergone PK.

CCT did not correlate significantly with IOP measured with any of the instruments. PDCT was the only instrument that did not show significant correlation with corneal astigmatism. None of the instruments took measurements that correlated with corneal astigmatism in eyes with sutures in situ or eyes that had undergone PK less than one year prior.