Delayed Appearance of High Altitude Retinal Hemorrhages

When closely examined, a very large amount of climbers exhibit retinal hemorrhages during exposure to high altitudes. The incidence of retinal hemorrhages may be greater than previously appreciated as a definite time lag was observed between highest altitude reached and development of retinal bleeding. Retinal hemorrhages should not be considered warning signs of impending severe altitude illness due to their delayed appearance

Laser Doppler Flowmetry versatile acquisition system with low quantization error

The Laser Doppler Flowmetry (LDF) is a non-invasive technique used to evaluate blood perfusion of various human tissues like the skin or the fundus of the eye. It is based on the scattering of light on moving red blood cells in tissue. Frequency shifted scattered light is detected and provide an electrical signal. Physical models for LDF use the DC and AC components of this signal. If AC is small relative to the DC, digitalization becomes an issue, and if more than two LDF signal acquisitions and analysis have to be done simultaneously, the device becomes expensive and bulky. We propose here a versatile and inexpensive acquisition system, which overcomes quantization errors issue by first separating DC from AC, then amplifying AC and finally recombining both signals before digitalization. We designed an analog circuit combined with a 12 bit analog-to-digital converter, a microcontroller unit and a Raspberry Pi2 (Rpi2) for the signal processing. Results are accessed remotely from the Rpi2 through HTTP protocol. Multiple systems can easily be used simultaneously for multichannel acquisitions

Maximum possible contrast level for silent substitution ::a theoretical model applied to melanopsin stimulation

For any given set of light sources stimulating the photoreceptors of the retina, the theoretical levels of illumination producing the smallest and the largest expression of one photoreceptor with fixed stimulation for the others are analytically computed. The cases of four, five, and more light sources are studied. We show that, for contrast optimization, only as many light sources as photoreceptors do matter and that, in the case of four light sources, the maximum contrast achievable for melanopsin lies at the intersection of the lines joining the sources in the CIE xy chromaticity diagram. This result is used to obtain the optimal position of four Gaussian primaries of equal bandwidth. In addition, we derive a procedure to construct level maps for melanopsin contrast overlying the diagram. In the second part of the paper, the interpersonal variability of the perceived stimulation is shown to be globally reduced if the bandwidth of the light sources is increased and, under some assumptions, if a light source is added

Development of interferometer for refractive index measurement of aqueous solution in a microfluidic chip

This study presents the design and development of an interferometer for the measurement of the refractive index or concentration of a sub-microliter volume of aqueous solution in a microfluidic chip. This proposed interferometer is manifested by the successful measurement of the refractive index of a sugar–water solution, using a He–Ne laser as a light source and robust instrumentation for practical implementation. The measurement principle and the feasibility of the system are analyzed theoretically. The experimental device is constructed with a He–Ne laser, two lenses, two optical plates and a complementary metal oxide semiconductor detector. The refractive index change is determined by measuring the positional changes of the interference fringes. A refractive index change of 10−4 is inferred from the measured image data

Device for silent substitution excitation of melanopsin for human eye

Research in neurobiology has identified a new ocular photoreceptor (melanopsin or ipRGC) which mediates a variety of light-based, non-visual effects on human physiology. One way to isolate the stimulation of ipRGCs is the silent substitution technique. We have built a Maxwellian view device capable of 85% ipRGCs contrast excitation with a large FOV (52o). Four modulated LED light sources, illuminate a diffusing sphere, which exit aperture is imaged into the pupil of the eye. A camera with a 900 nm illumination capture the pupil. Without luminance changes (510±2 lm/m2), we increased ipRGC excitation from low to high level on three subjects. We observed a pupil constriction increasing with the ipRGC contrast. This suggests that we excite melanopsin silently. However, further experiments with electrophysiological and pupil recording needs to be done to completely validate our silent substitution device

Schlieren laser Doppler flowmeter for the human optical nerve head with the flicker stimuli

We describe a device to measure blood perfusion for the human optic nerve head (ONH) based on laser Doppler flowmetry (LDF) with a flicker stimuli of the fovea region. This device is self-aligned for LDF measurements and includes near-infrared pupil observation, green illumination, and observation of the ONH. The optical system of the flowmeter is based on a Schlieren arrangement which collects only photons that encounter multiple scattering and are back-scattered out of the illumination point. LDF measurements are based on heterodyne detection of Doppler shifted back-scattered light. We also describe an automated analysis of the LDF signals which rejects artifacts and false signals such as blinks. By using a Doppler simulator consisting of a lens and a rotating diffusing wheel, we demonstrate that velocity and flow vary linearly with the speed of the wheel. A cohort of 12 healthy subjects demonstrated that flicker stimulation induces an increase of 17.8% of blood flow in the ONH

Forward osmosis in a portable device for automatic osmolality adjustment of environmental water samples evaluated by cell-based biosensors

Forward osmosis (FO) is a well-established process that has been used for different applications like desalination of water, concentration of foods or drugs, and energy harvesting. We exploited this process in a fully automatic system to adjust osmolality of environmental water samples that are to be tested by cell-based biosensors. In cell-based biosensors, samples are brought into contact with living cells. Therefore, the samples osmolality and should be in a range that is tolerable for the cells. Controlling these parameters has been a significant challenge especially in environmental monitoring, where the biosensors are required to work on-site. In this paper, we introduce a low-cost portable fluidic system that works automatically, and adjusts the osmolality and pH of environmental samples without diluting or denaturizing the ingredients of the samples. We report the performance of this system in adjusting the osmolality and pH of Swiss environmental waters with a natural osmolality of 4 1 mmol/kg and a pH of 7.84 +/- 0.02. (c) 2013 Elsevier B.V. All rights reserved

Forward osmosis in a portable device for automatic osmolality adjustment of environmental water samples evaluated by cell-based biosensors

Forward osmosis (FO) is a well-established process that has been used for different applications like desalination of water, concentration of foods or drugs, and energy harvesting. We exploited this process in a fully automatic system to adjust osmolality of environmental water samples that are to be tested by cell-based biosensors. In cell-based biosensors, samples are brought into contact with living cells. Therefore, the samples' osmolality and pH should be in a range that is tolerable for the cells. Controlling these parameters has been a significant challenge especially in environmental monitoring, where the biosensors are required to work on-site. In this paper, we introduce a low-cost portable fluidic system that works automatically, and adjusts the osmolality and pH of environmental samples without diluting or denaturizing the ingredients of the samples. We report the performance of this system in adjusting the osmolality and pH of Swiss environmental waters with a natural osmolality of 4±1 mmol/kg and a pH of 7.84±0.02

Compact Laser Doppler Flowmeter (LDF) Fundus Camera for the Assessment of Retinal Blood Perfusion in Small Animals

International audienceNoninvasive techniques for ocular blood perfusion assessment are of crucial importance for exploring microvascular alterations related to systemic and ocular diseases. However, few techniques adapted to rodents are available and most are invasive or not specifically focused on the optic nerve head (ONH), choroid or retinal circulation. Here we present the results obtained with a new rodent-adapted compact fundus camera based on laser Doppler flowmetry (LDF)