V 431
The influence of corneal thickness on applanation error in eyes with pathologic corneas
F. Madjlessi, W. Marx, T. Reinhard, C. Althaus
Background: Recently, we have been able to demonstrate, that applanation tonometry delivers mostly false low results in corneal pathology. The influence of corneal thickness on applanation error in normal corneas is discussed controversely. It was the aim of this study to evaluate the influence of corneal thickness in corneal pathology on applanation error.
Patients and methods: In 100 eyes with different corneal pathology we performed intraocular needle tonometry after applanation tonometry and ultrasound pachymetry.
Results: The mean of applanation tonometry was 4.3 ± 5.7 mm Hg below true intraocular pressure as measured by needle tonometry. Corneal thickness was between 271µm and 1200 µm. In corneas with edema, corneal thickness correlated significantly negative with the applanation error which means the thicker the edematous cornea the lower the sampling error. This correlation was not to be found in corneal transplants with or without edema.
Conclusion: Presence of corneal edema is responsible for false low applanation measurements. This sampling error is diminished in corneas - but not in corneal transplants! - by increasement of corneal thickness. The reason for the different behaviour of corneal transplants has to be examined in further studies.
Eye-department, Heinrich Heine University, Moorenstr. 5, D-40225 Düsseldorf