Comparison of Intraocular Pressure Measurements between Icare Pro Rebound Tonometer and Tono-Pen XL Tonometer in Supine and Lateral Decubitus Body Positions

Purpose: To compare intraocular pressure (IOP) measurements obtained using the Icare Pro rebound tonometer and Tono-Pen XL tonometer in supine and lateral decubitus body positions. Methods: One-hundred eyes of 50 subjects (normal volunteers or glaucoma suspects) were enrolled in this prospective observational study. IOP was measured in both eyes using the Icare Pro and Tono-Pen XL in the sitting position and the recumbent positions including supine, right lateral decubitus and left lateral decubitus. IOP was measured five minutes after assuming each of the recumbent postures in a randomized sequence. The eye on the lower side in the lateral decubitus position was termed as the dependent eye. Agreement of IOP readings between the Icare Pro and Tono-Pen was assessed in all recumbent positions. Differences of IOP readings (Delta IOP) between the two tonometers and their correlations with ocular parameters were also assessed in all positions. Results: The IOP readings obtained using Icare Pro and Tono-Pen showed good correlations in supine and lateral decubitus positions (all r>0.7, p<0.005), although Icare Pro readings were higher than Tono-Pen readings (all p<0.001) in all positions. The DIOP showed a weakly positive correlation with central corneal thickness in both eyes, whereas such a positive correlation was found only in the dependent eye in the lateral decubitus positions (r=0.307-0.531, all p<0.005). Both the spherical equivalents and axial lengths were not correlated with Delta IOP in all positions. Conclusion: IOP readings obtained with Tono-Pen and Icare Pro tonometers showed good agreement in supine as well as in lateral decubitus positions, although Icare readings were higher than Tono-Pen readings in all positions. Such differences in IOP readings between the different tonometers need to be considered when measuring IOPs in various body positions.