A standard problem in large tanks at oil refineries and petrol stations is that water and fuel usually occupy the same tank. This is undesirable and causes problems such as corrosion in the tanks. Normally, the water level in tanks is unknown, with the problems that this entails. We propose herein a method based on surface plasmon resonance (SPR) to detect in real time the interfaces in a tank which can simultaneously contain water, gasoline (or diesel) and air. The plasmonic sensor is composed of a hemispherical glass prism, a magnesium fluoride layer, and a gold layer. We have optimized the structural parameters of the sensor from the theoretical modeling of the reflectance curve. The sensor detects water-fuel and fuel-air interfaces and measures the level of each liquid in real time. This sensor is recommended for inflammable liquids because inside the tank there are no electrical or electronic signals which could cause explosions. The sensor proposed has a sensitivity of between 1.2 and 3.5 RIU⁻¹ and a resolution of between 5.7 × 10⁻⁴ and 16.5 × 10⁻⁴ RIU.

To evaluate the optical image quality, using 2 optical devices (an aberrometer and a double-pass device), and visual performance [contrast sensitivity function (CSF)] in patients with keratitis and after resolution of the disease. Twenty subjects with keratitis (18 patients with unilateral keratitis and 2 patients with bilateral keratitis) were included in this study. We also took measurements in healthy fellow eyes for comparison. Ten patients were studied before and after the resolution of keratitis. Objective data were gathered by aberrometry (ocular higher order, spherical, and coma aberrations) and the Strehl ratio, a parameter derived from the double-pass device that included information on diffraction, ocular aberrations, and scattering. The CSF was also measured for all the patients. Ocular higher order, spherical, and coma aberrations in keratitis eyes were significantly (P < 0.05) higher than those in healthy fellow eyes. The Strehl ratio indicates a worse optical quality for keratitis eyes being significantly (P < 0.05) lower than the Strehl ratio for healthy fellow eyes. CSF for keratitis eyes was also significantly lower than that for the healthy eyes (P < 0.05). Data for keratitis eyes after the resolution of the disease showed a significant increase in the optical function and visual performance but, after treatment, continued to suffer significant (P < 0.05) impairment in the optical quality of the affected eyes compared with the healthy fellow eyes. Devices to measure optical image quality and the CSF enable the characterization of the optical quality and visual performance in patients with keratitis, showing a significant decline in optical quality and visual performance during keratitis and an improvement after the resolution of the pathology.