[Correction factors for central corneal thickness in Goldmann applanation tonometry]

For many years researchers have discussed which corneal parameters can influence the measurement of intraocular pressure (IOP). As a substantial parameter, the central corneal thickness (CCT) is assumed; however, different measuring methods - including Goldmann applanation tonometry (GAT), dynamic contour tonometry (DCT), and corneal compensated pressure measured with the ocular response analyzer (IOPcc) - may lead to a completely different dependence on corneal thickness.

In a study approved by the ethics commission, the anterior chamber of 92 eyes of cataract patients and 85 eyes of glaucoma patients with very different CCT measurements was cannulized before surgery (cataract operation or trabeculectomy), and the IOP values were measured simultaneously with a pressure absorber and with GAT (Perkins tonometer) at different pressure values.

The individual measurements exhibited an extraordinarily wide dispersion. In both groups, weak correlations of the difference between GAT and IOP values with the CCT were found (correction factors of 0.95 mmHg/100 microm CCT at pressure level 20 mmHg, 1.2 mmHg/100 microm CCT at pressure level 30 mmHg, and 1.7 mmHg/100 microm CCT at pressure level 40 mmHg).

Measurement of CCT is valuable for prognostic assessment of glaucoma, but not for correction factors for corneal thickness.