Assessment of conjunctival, episcleral and scleral thickness in healthy individuals using anterior segment optical coherence tomography.

PURPOSE: To determine the thickness of the conjunctiva, episclera and sclera in healthy individuals using anterior segment optical coherence tomography (AS-OCT). METHODS: We prospectively included 107 healthy individuals of different age groups (18-39 years, 40-54 years, 55-69 years and ≥70 years). For each eye, AS-OCT scans of four quadrants (temporal, nasal, superior and inferior) were acquired. The thickness of the conjunctiva, episclera and sclera was measured for each scan. In addition, the axial length of both eyes was measured, and general characteristics, including smoking, allergies and contact lens use, were collected. RESULTS: The mean conjunctival thickness was significantly different between the nasal and superior quadrants (87 ± 30 µm vs. 77 ± 16 µm; p < 0.001), as well as the superior and inferior quadrants (77 ± 16 µm vs. 86 ± 19 µm; p = 0.001). The mean episcleral thickness was larger in the superior (174 ± 54 µm) and inferior (141 ± 43 µm) quadrants, compared to the nasal (83 ± 38 µm) and temporal quadrants (90 ± 44 µm). The mean scleral thickness of the inferior quadrant was the largest (596 ± 64 µm), followed by the nasal (567 ± 76 µm), temporal (516 ± 67 µm) and superior (467 ± 52 µm) quadrants (all p < 0.001). The averaged scleral thickness increased 0.96 µm per age year (0.41-1.47 µm, p < 0.001). CONCLUSIONS: This study provides an assessment of the thickness of scleral and adjacent superficial layers in healthy individuals determined on AS-OCT, which could enable future research into the use of AS-OCT in diseases affecting the anterior eye wall.

Fast optical source for quantum key distribution based on semiconductor optical amplifiers.

A novel integrated optical source capable of emitting faint pulses with different polarization states and with different intensity levels at 100 MHz has been developed. The source relies on a single laser diode followed by four semiconductor optical amplifiers and thin film polarizers, connected through a fiber network. The use of a single laser ensures high level of indistinguishability in time and spectrum of the pulses for the four different polarizations and three different levels of intensity. The applicability of the source is demonstrated in the lab through a free space quantum key distribution experiment which makes use of the decoy state BB84 protocol. We achieved a lower bound secure key rate of the order of 3.64 Mbps and a quantum bit error ratio as low as 1.14×10⁻² while the lower bound secure key rate became 187 bps for an equivalent attenuation of 35 dB. To our knowledge, this is the fastest polarization encoded QKD system which has been reported so far. The performance, reduced size, low power consumption and the fact that the components used can be space qualified make the source particularly suitable for secure satellite communication.

Estimation of the standard deviation in three-dimensional microscopy by spatial statistics.

Usually, the calibration process for three-dimensional microscopy involves the use of a reference flat surface. The random fluctuations of the topographic image for this reference surface are used for determining the uncertainty of the microscope. When the sample material or the measuring conditions of the microscope are modified (such as the objective used in a confocal microscope, or the tip in an atomic force microscope), the measuring conditions vary and thus a new calibration is required. In this work, a technique based on spatial statistics methods (more specifically, the variogram function) is proposed to determine accurately the standard deviation for three-dimensional microscopy that does not require a reference flat surface and therefore eliminates the need for a previous calibration process of this parameter.

Optical technique for the automatic detection and measurement of surface defects on thin metallic wires.

In industrial applications of thin metallic wires it is important to characterize the surface defects of the wires. We present an optical technique for the automatic detection of surface defects on thin metallic wires (diameters, 50-2000 microm) that can be used in on-line systems for surface quality control. This technique is based on the intensity variations on the scattered cone generated when the wire is illuminated with a beam at oblique incidence. Our results are compared with those obtained by atomic-force microscopy and scanning-electron microscopy.

Histogram-based method for contrast measurement.

A histogram-based technique for robust contrast measurement is proposed. The method is based on fitting the histogram of the measured image to the histogram of a model function, and it can be used for contrast determination in fringe patterns. Simulated and experimental results are presented.

Modulation transfer function of translucent rough sheets.

Rough surfaces in translucent protective sheets are used in imaging systems, such as displays, to decrease specular reflections of external sources. However, they modify the quality of the images formed by transmission. Using a geometric approximation, we have modeled the behavior of rough surfaces in imaging systems. This model provides an analytical expression for the modulation transfer function of rough surfaces.