Developments and Progress in Non-contact Eye Tonometer Calibration

Abstract

This paper focuses on the problematic of intraocular pressure (IOP) measurements, performed by non-invasive methods. More specifically, the devices that are connected with the presented finding are non-contact tonometers that use concentrated air stream and optical sensors to determine the IOP within a human’s eye. The paper analyzes various influential factors that have an effect on the determination of the IOP values originating from the patients themselves and from the non-contact tonometer devices. The paper furthermore elaborates on the lack of independent methods of calibration and control of these devices. In order to fill this gap a measurement standard device that is capable of calibrating and testing these devices with traceability to the basic SI unit is presented. A detailed characterization and the determination of the expected uncertainty of the device are provided. By introducing an independent and traceable calibration method and control of non-contact tonometers into the clinical practice, the reliability of the measured IOP that is the primary indicator of glaucoma can be improved.

Corrosion Resistance of AISI 316L Stainless Steel Biomaterial after Plasma Immersion Ion Implantation of Nitrogen

“…This corresponds with the results of both electrochemical corrosion tests and points to the abovementioned positive role of nitrogen in the pit repassivation process (Section 3.2). Recorded low corrosion rates also indicate a potentially negligible leakage of harmful substances into the human body [26][27][28][29][30] and suggest a high biocompatibility of PIII nitrided surfaces [11].…”

Factors Affecting Measurements of IOP Using Non-Contact Eye Tonometer

“…The duration of pressure application is recorded by optical means; more specifically by an infrared light source that is reflected into the detector upon reflection from the flattened cornea, during the application the detector detects higher power from the pressure source than when reflected from the cornea of an unexposed air stream which is normally convex. The IOP calculation is done by the device, by using the time of the application at the pressure value generated by the air flow [1,8].…”

“…By defining their interaction we can increase the resulting uncertainty, but also significantly reduce it. It all depends on the nature of whether the uncertainty components act in agreement or disagreement on the two uncertainty estimates under consideration; in particular, the values generated from the non-contact eye tonometer will be correlated with each other [1,8].…”

“…1 Comparison of difference artificial cornea thicknesses and their effect on the IOP measurement by a clinically tested non-contact tonometer NidekNT2000. [ 8] The Fig. 1 shows how the set pressure by the developed standard corresponds with the indicated IOP pressure by a clinically tested non-contact tonometer Nidek NT 2000.…”

“…The use of higher thicknesses had caused a more significant deviation and the decreasing the thickness to 0.3 mm had shown no benefit but has caused instability at higher pressures. It should be noted that the 0.7 mm thick cornea has caused the absence of an applanation and therefore no data could be measured [1,8].…”