Dental impressions are widely used in the field of oral restoration. The materials are used for making impression in oral cavity. In order to measure the thickness of impression for reference in clinic, the real impressions are taken as the object for studying. Through optical method, charge-coupled device (CCD) is used for collecting the grey image of cutting section of the impressions which are located in the same plane with steel dividing ruler. According to convert relationship between dividing ruler and pixels collecting grey image, the thickness of impression specimens can be obtained. The results show that the optical method used for measuring thickness is feasible to the task and the precision can reach micro dimension. The experiment method and technique can also be provided for measuring thickness of similar tissue engineering materials.
We conducted this study to explore the influence of the ocular residual aberrations changes on contrast sensitivity (CS) function in eyes undergoing orthokeratology using adaptive optics technique. Nineteen subjects' nineteen eyes were included in this study. The subjects were between 12 and 20 years (14.27±2.23 years) of age. An adaptive optics (AO) system was adopted to measure and compensate the residual aberrations through a 4-mm artificial pupil, and at the same time the contrast sensitivities were measured at five spatial frequencies (2,4,8,16, and 32 cycles per degree).The CS measurements with and without AO correction were completed. The sequence of the measurements with and without AO correction was randomly arranged without informing the observers. A two-interval forced-choice procedure was used for the CS measurements. The paired t-test was used to compare the contrast sensitivity with and without AO correction at each spatial frequency. The results revealed that the AO system decreased the mean total root mean square (RMS) from 0.356 μm to 0.160 μm(t=10.517, P＜0.001), and the mean total higher-order RMS from 0.246 μm to 0.095 μm(t=10.113, P＜0.001). The difference in log contrast sensitivity with and without AO correction was significant only at 8 cpd (t=-2.51, P=0.02). Thereby we concluded that correcting the ocular residual aberrations using adaptive optics technique could improve the contrast sensitivity function at intermediate spatial frequency in patients undergoing orthokeratology.
In photoacoustic imaging the ultrasonic signals are usually detected by contacting transducers. For some applications, contact with the tissue should be avoided, e.g. in those of brain functional imaging. As alternatives to contacting transducers interferometric techniques can be used to acquire photoacoustic signals remotely. Here, a system for non-contact photoacoustic tomography imaging (NCPAT) has been established. This approach enables NCPAT not to exceed laser exposure safety limits. The stimulated source of NCPAT utilized a laser with center wavelength of 532 nm and output intensity of 17.5 mJ/cm2, and a laser heterodyne interferometry was used to receive the photoacoustic signals. The NCPAT was used to implement on a rotational imaging geometry for photoacoustic tomography with a real-tissue phantom. The photoacoustic imaging was obtained by applying a reconstruction algorithm to the data acquired for NCPAT. Experiments results showed that the NCPAT system with detection 15 dB bandwidth of 2.25 MHz could resolve spherical optical inclusions with dimension of 500 μm and multi-layered structure with optical contrast in strongly scattering medium. The method could expand the scope of photoacoustic and ultrasonic technology to in-vivo biomedical applications where contact is impractical.
Adaptive optics (AO) is a technique to improve the performance of optical systems by reducing the influence of optical aberrations. Combined with scanning laser ophthalmoscope (AOSLO), the aberration of human refractive system can be corrected. Thus, the resolution and quality of imaging can be greatly improved to the cellular level in vivo retina (such as photoreceptor, nerve fibers, vascular parietal cell), therefore the earlier changes of the diseases can be detected. At the same time, microstructure changes of retinal can also be observed during the follow-up of the disease. Due to inherent technical defects of AOSLO, its wide application in clinical practice is limited. With the continuous progress of AO technology and the further improvement of related software functions, the function of the system will become more stronger and will play a more and more important role in scientific research and clinic.
ObjectiveTo evaluate whether there are changes in cone cells in patients with pre-clinical hydroxychloroquine (HCQ) retinopathy using an adaptive optics (AO) retinal camera. MethodsA retrospective case-control study. From May 2020 to July 2020, 46 patients who were treated in Department of Rheumatism and Immunology, Hainan Hospital of PLA General Hospital with rheumatic immune diseases were included. All patients had a history of HCQ use and no obvious abnormality was found in fundus examination; 105 healthy people with similar demographic characteristics without a history of hydroxychloroquine were recruited as the control group were included. All subjects received the routine ophthalmological examination including best corrected visual auity (BCVA), spectral-domain optical coherence tomography (SD-OCT), Fundus autofluorescence (FAF), visual field, endoscopy of the cornea, and the measurement of axial length (AL). The BCVA was performed with the Snellen visual acuity chart, and the result was converted to logarithmic minimum angle of resolution (logMAR) visual acuity for statistic. Among the 46 cases, 6 cases were males and 40 cases were females. Age was (42.02±13.81) years old; logMAR BCVA was 0.063±0.015; AL was (23.95±0.726) mm. Visual field, macular SD-OCT, FAF examination showed no abnormality. The average cumulative dose of HCQ was 522.60 (6-1 728) g. rtx1 AO retinal camera was used to collect fundus images of subjects in four quadrants above the retina, nasal side, lower side and temporal side with 3°centrifugation from the fovea in both eyes. The cone density, cone spacing, cone arrangement regularity and the proportion of the nearest cones with 6 (nn=6) were measured in the four quadrants. The density of cone cells between the left and right eyes in case group and control group were compared by paired t test. The density and spacing of cone cells in each quadrant were compared by t test of two independent samples. ResultsCompared with the control group, the cone cell density in the four quadrants of the left eye and the nasal, superior and inferior sides of the right eye in the case group was significantly decreased, and the difference was statistically significant (t=4.247, 2.107, 4.884, 2.254, 2.643, 4.445, 4.116; P＜0.05). The cone spacing in the nasal and temporal sides of the left eye of the patients in the case group was significantly larger than that in the control eye, with statistical significance (t=2.750, 3.318; P＜0.05). Compared with the control group, the regulatign of cone cell arrangement in the left temporal side of the right and left eye in the case group were significantly reduced, the difference was statistically significant (P=0.002, 0.011). The proportion of nn=6 in the inferior and temporal sides of the right eye decreased significantly in the case group, and the difference was statistically significant (P=0.006, 0.032). ConclusionAO retinal imaging can detect the changes of cone cells in the early clinical stage of HCQ retinopathy.
As a newly developing technology of adaptive optics (AO), the combination of AO technology with traditional fundus imaging devices, such as fundus camera, scanning laser ophthalmoscope as well as optical coherence tomography, can image photoreceptor cells, retinal pigment epithelial cells, retinal ganglion cells, and retinal vascular system. Currently, AO technology is applied in the diagnosis, monitor and management of retinal diseases, enabling the observation of early changes of photoreceptor cells and analyzing vascular parameters in inherited retinal diseases, age-related macular degeneration, retinal vascular diseases such as diabetic retinopathy and retinal vein occlusion, inflammatory retinal diseases and central serous chorioretinopathy. Major breakthrough brought by AO technology along with rapid progress driven by ophthalmic imaging devices can help clarify the pathogenesis of eye diseases. and offer a comprehensive understanding of the new perspectives provided by AO technology for fundus imaging. Of course, limitation of popularizing application of AO device exists due to small scan range and optic media opacity. Thus, a comprehensive understanding of AO technology provides a new horizon for retina imaging. A comprehensive understanding of AO technology provides updated vision for fundus imaging, and is expected to promote the clinical application of AO technology in ophthalmology, and to enable cellular-resolution imaging of the living human retina.