China
Africa
Explore chapters and articles related to this topic
Lung Microcirculation
Published in John H. Barker, Gary L. Anderson, Michael D. Menger, Clinically Applied Microcirculation Research, 2019
Andrew M. Roberts, Dick W. Slaaf
Microscopic images are obtained using a trinocular microscope (Leitz) designed for incident illumination (Figure 1). A color CCD video camera (Sony DXC-101; 2/3 inch) is positioned in the image plane of the objective lens (Leitz: L10 iris, numerical aperture 0.22). Total optical magnification is 10×. Images are displayed on a color video monitor (Sony Trinitron; 12-inch model PVM 1390) and stored on videotape for off-line analysis using a video cassette recorder (JVC HR-D660U). Total magnification of the image on the video monitor is 680× with a field of view of 380 × 285 µm. Incident illumination is achieved using a Leitz Ploemopak system (tube-factor 1×) equipped with a POL-cube (see Figure 1). The light source is a 100-W mercury arc lamp connected to a stabilized power supply (Leitz HBO 100 #990014). The light passes a heat absorption and a heat reflection filter that minimizes heating the preparation. The light passes a polarizer and is brought to the optical axis of the microscope by reflection from a 50% mirror positioned at a 45° angle with the optical axis of the microscope. Light coming from the preparation passes the 50% reflective mirror and a crossed analyzer and forms an image on the camera. The combination of the polarizer and crossed analyzer cancels all directly reflecting light.37
Photography of the nail unit
Published in Archana Singal, Shekhar Neema, Piyush Kumar, Nail Disorders, 2019
Sanjeev Gupta, Kartikay Aggarwal
A ring flash (Figure 38.8) is a circular photographic flash that fits around a camera lens. Its salient feature is that it provides even illumination with very few shadows visible in the resulting photographs. This is due to the origin of light being near to the optical axis of the lens. The much higher-quality results obtained with a ring (O-ring-type) flash are yet another reason for dermatologists to choose an DSLR camera over a compact or mirrorless model.
Foundations of motion analysis
Published in Paul Grimshaw, Michael Cole, Adrian Burden, Neil Fowler, Instant Notes in Sport and Exercise Biomechanics, 2019
To limit the effect of perspective error, the optical axis of the camera (i.e. an imaginary line passing through the middle of the lens) must be oriented at 90 degrees to the intended plane of motion (Figure H5.5a). Assuming that the plane of motion is vertical (e.g. during running), this can be partly achieved by placing a spirit level on top of the camera and positioned both parallel and perpendicular to its optical axis. Of course, this assumes that the top surface of the camera is both horizontal and level. If not, the height of the centre of the lens can be measured and a marker placed in the plane of motion at the same height. The lens can then be zoomed in on the marker, which should remain in the middle of the image. When the required field of view is confirmed, the bottom of the image should also be parallel with a line that is known to be horizontal (e.g. the ground). A 3–4–5 triangle (or multiples thereof) can be used to ensure that the optical axis is aligned at 90 degrees to the plane of motion, in the horizontal plane (Figure H5.5b). A plumb line should be used to ensure that the apex of the triangle, or a line extending from this point, is positioned directly below the centre of the lens (i.e. the optical axis).
Instant vision assessment device for measuring refraction in low vision
Published in Clinical and Experimental Optometry, 2021
Since the aim of the IVAD is to test subjective central refraction (i.e. the sharpest stimulus optotype on the fovea), the design has been optimised to provide a diffraction-limited image on-axis. The off-axis distribution should not affect the measurements of the study because the image tested is relatively small (less than 1 degree of visual angle) as compared to the isoplanatic patch of the system9 which covers 5 degrees, i.e. the overall foveal region (Figure 3 for the ray-tracing justification). Therefore, the optical variation away from the optical axis (i.e., pupil position, spherical and cylindrical errors) is of little relevance to this study. The magnification and exit pupil diameter of the telescope changed from 1.7x and 13.5 mm at the shortest length to 2.7x and 8.5 mm at the longest length, respectively. The back-vertex power of the telescope at each length setting was calibrated by the Zemax Program and measured by a focimeter.10
Modern spectacle lens design
Published in Clinical and Experimental Optometry, 2020
When a narrow pencil of rays is refracted obliquely by a spherical surface, the refracted pencil becomes astigmatic. Instead of the rays re‐uniting in a single image point, they form two‐line foci at right angles to one another and between them, where the refracted pencil has its least cross‐sectional area – a disc of least confusion. The plane containing the optical axis of the surface is referred to as the tangential plane and the plane at right angles to this is referred to as the sagittal plane. The tangential and sagittal oblique vertex sphere powers of a spectacle lens are determined by accurate trigonometric ray tracing through the lens. The chief ray passes through the centre of rotation of the eye which is supposed to lie on the optical axis of the lens. It is also assumed that the primary line of sight coincides with the optical axis.2016 When it does not, as would be the case when the lens is tilted or decentred before the eye – for example, when a pantoscopic or face form tilt is applied to the lens – more complicated ray tracing techniques must be applied, which invariably requires the use of computer software to trace skew rays through the lens.2016
Analysis of Corneal Astigmatism before Surgery in Chinese Congenital Ectopia Lentis Patients
Published in Current Eye Research, 2018
Yichi Zhang, Guangming Jin, Charlotte Aimee Young, Qianzhong Cao, Junxiong Lin, Jianqiang Lin, Yiyao Wang, Danying Zheng
Furthermore, our results show that eyes of CEL patients with Marfan syndrome have significantly more corneal astigmatism than CEL patients without Marfan syndrome. It is generally expected that the main cause of refractive astigmatism in eyes with CEL is from lenticular astigmatism because the displacement of the lens may cause optical axis and lens tilting. However, in the current study, we revealed that CEL eyes with Marfan syndrome also have significantly increased corneal astigmatism compared with CEL eyes without Marfan syndrome. This is consistent with previous studies19,20, which reported that eyes with Marfan syndrome have flatter and thinner corneas with higher corneal astigmatism than normal eyes. However, the potential physiological or pathological mechanisms of this finding are still unclear. It may be that the same mechanisms that cause zonular instability and EL can also cause defects in corneal tissue and therefore increase corneal astigmatism. To add, our study found a positive correlation between age and corneal astigmatism in CEL patients. In previous studies, negative correlation has been reported between age and corneal astigmatism in adult and pediatric cataract patients.16 The difference between the results of this study and previous studies may be explained by the difference in the subjects. In EL patients, the underlying pathological mechanisms causing zonular instability in EL may also result in increased corneal astigmatism, and the corneal astigmatism increases as the eyeball develops. However, more clinical and laboratory studies are needed to illustrate this mechanism.