Die Rolle der Pachymetrie in der täglichen Glaukomdiagnostik

The influence of corneal thickness on the precision of Goldman applanation tonometry is highly disputed. Goldmann and Schmidt assumed that the physiological variation of corneal thickness does not influence the measurement. But they indicated that an "abnormal" deviation of corneal thickness can lead to a false measurement. In the last 30 years many investigations have reliably demonstrated that thick corneas produce elevated applanation values and thin corneas lower values. The correation value is 1 mm Hg per 25 μm change in corneal thickness. The accuracy of intraocular pressure measurement is important for the detection and monitoring of glaucoma. Therefore it is necessary to recalculate applanation values based on corneal thickness in every patient, especially after refractive surgery. It is also necessary to keep in mind that with applanation tonometry we measure a force. From the force readings we deduce the value of the intraocular pressure. This conclusion is only correct if the theory of Goldmann applanation tonometry is right. But between force measurement and intraocular pressure there is the individual cornea with special properties like thickness, rigidity and astigmatism which can influence the correctness of the measurement. So we can understand why knowledge of corneal thickness can improve the deduction from force measurement of intraocular pressure. It is also reasonable that other individual corneal properties we do not measure or do not know so far can influence the deduction. This means that the corneal thickness is not the only variable. Pachymetry allows us to estimate the intraocular pressure with higher precision. Therefore it should be clinically used.