Development And Evaluation Of A Multi-Force Sensor Based Trans-Palpebral Tactile Tonometer

Glaucoma is a group of diseases that lead to a progressive loss of vision in the majority of the cases due to elevated intraocular pressure (IOP). Glaucoma is the second leading cause of blindness after cataract. According to the National Eye Institute's report, there were almost 2.7 million detected cases in the United States in 2010.Everybody older than 40, African Americans and Hispanics at any age, are at high risk and would need frequent IOP measurement in order to diagnose the disease at an early stage. Majority of the existing tonometers measure the IOP through the cornea and their operation requires clinical professionals. As a result, the measurement has to take place at the doctor's office and requires local anesthesia. This work demonstrates a novel multi-probe tactile-tonometer, which is operated by the patients and measures the IOP through their eyelid. Finite element (FE) models were used to estimate the static, mechanical response of the eye, due to indentation at different IOPs. The models include hyperelastic behavior of the sclera and cornea. The thickness variation of the sclera, throughout the geometry was also considered. Volumetric constraint was applied on the eye cavity, but its actual anatomic structure was neglected. In-vitro indentation tests were performed on enucleated porcine eyeballs, as a proof of concept of tactile-tonometry. Eye/patient specific calibration method was demonstrated, in order to further improve accuracy ("Forward Biomechanics"), and in-vivo estimation of biomechanical properties of the eye ("Inverse Biomechanics"). The method uses simplified FE models and a feed forward artificial neural network (ANN). The tactile-tonometer was implemented for human use, and clinical studies were performed on a small number (10) of human subjects. Based on the measurements from the recruited 10 patients (3 females, 7 males) with a mean age ±SD of 43±19.33 and the measured IOP range of 9.25-21.25mmHg, the novel technique has a mean of differences of ≈ 0mmHg and its 95% limits of agreement are ±4.84mmHg with respect to the Goldmann Applanation Tonometer