Effect of corneal thickness on applanation tonometry in glaucoma patients
B. Roesen, S. J. Fröhlich, C. Niederdellmann, S. Ullrich, M. Bechmann
Purpose: Goldmann applanation tonometry is based on the Imbert-Fick law, which assumes that the surface of the cornea is perfectly elasitc and thin so the intraocular pressure could be measured by applanation of the cornea. The design of the tonometer was based on the central corneal thickness (CCT) of 520µm. Thinner or thicker CCTs could lead to an under- or overestimation of the IOP.
Methods: In addition to the clinical examination we determined in 132 consecutive controls and patientes with ocular hypertension (OHT), primary open-angle glaucoma (POAG) and normal tension glaucoma (NTG) the CCT by ultrasonic pachymetry.
Results: Mean CCT of the control eyes was 573 µm ± 34, the mean CCT of the eyes with POAG was 570 ± 39. The eyes with LTG had with a CCT of 548 µm ± 44 a significant lower CCT than the POAG group. The eyes with OH had a significant thicker cornea than the POAG group (627 µm ± 28, p£ 0,001).
Conclusion: In patients with OHT, NTG and in patients with POAG with regulated IOP and deterioration of the visual field the CCT can help to interpred the results of the Goldmann applanation tonometry.
Department of Ophthalmology, Ludwig-Maximilians-Universität, Munich, Mathildenstr. 8, 80336 Munich, Germany