Effect of Corneal Thickness, Curvature and Axial Length on Goldmann Applanation Tonometry

Abstract

Abstract: : Purpose: IOP measurement is an important parameter in the detection and monitoring of glaucoma. It is assumed that Goldmann tonometry is not influenced by ocular parameters such as corneal thickness, corneal curvature and axial length. Aim of this study was to examine if there is an influence of the mentioned ocular parameters on Goldmann tonometry. Methods: In a prospective clinical trial 125 eyes of 125 patients undergonig phacoemulsification (33 m and 92 w, mean age 72.91+/-13.2y, range 18 – 91y), with a corneal thickness of 568.8+/-43.79 (462 – 705) µm, with a corneal curvature of 7.72+/-0.27 (7.07 – 8.32) mm and an axial length of 23.62+/-2.05 (18.84 – 32.93) mm were examined. Before phacoemulsification the anterior chamber was canulated at the temporal corneal limbus. In a closed system the IOP was adjusted to 20, 35 and 50 mmHg by manometric watercolumn. IOP was measured with Perkins tonometer. Statistical analysis was performed with multiple regression analysis (SPSS). Results: At all IOP levels the IOP readings were highly dependend on corneal thickness (p<0.0001), R²: 0.78 – 0.83. At the IOP level of 20 mmHg corneal curvature effected the IOP measurement (p<0.037) but not at levels of 35 and 50 mmHg (p>0.05). Axial length had no effect on applanation tonometry at all IOP levels (p>0.05). The dependence of the IOP reading on corneal thickness is shown in the "Dresdner correction table". Conclusion: As corneal thickness effects Goldmann IOP readings we suggest that IOP readings should be corrected by corneal thickness according to the "Dresdner correction table" to obtain the true IOP value. This approach might be helpful in the detection and management of glaucoma.  

Keywords: intraocular pressure • cornea: clinical science • clinical research methodology