China
Africa
Explore chapters and articles related to this topic
Objective and Camera Lenses
Published in Robert J. Parelli, Principles of Fluoroscopic Image Intensification and Television Systems, 2020
An image created by the actual intersection of light rays is called virtual image.real image.magnified image.prism.
Noninvasive Tests
Published in Vineet Relhan, Vijay Kumar Garg, Sneha Ghunawat, Khushbu Mahajan, Comprehensive Textbook on Vitiligo, 2020
Hemant Kumar Kar, Gunjan Verma
The Woods lamp emits long-wave UV radiation (UVR), also called black light, generated by a high pressure mercury arc fitted with a compound filter made of barium silicate with 9% nickel oxide, the “Woods filter.” This filter is opaque to all light rays except a band between 320 and 400 nm with a peak at 365 nm. Fluorescence of tissues occurs when Woods (UV) light is absorbed and radiation of a longer wavelength, usually visible light, is emitted. The output of Woods lamp is generally low (<1 mw/cm2). The fluorescence of normal skin is very faint or absent and is mainly due to constituents of elastin, aromatic amino acids, and precursors or products of melanin [1,8].
Bioengineering Aids to Reproductive Medicine
Published in Sujoy K. Guba, Bioengineering in Reproductive Medicine, 2020
Entry angle e is equal to (90 - i). To have i large, e must be small. In other words, light rays with only small entry angles are transmitted (Figure 3.24). The maximum acceptance half angle
Steering light in fiber-optic medical devices: a patent review
Published in Expert Review of Medical Devices, 2022
Merle S. Losch, Famke Kardux, Jenny Dankelman, Benno H. W. Hendriks
Another possible fiber core end design is a conical shape as described in seven patents [23,38–43]. The cone can be polished either positively [23,38–41] or negatively [42,43]. For a standard positively polished tip, the conical surface forms an interface between two media: fiberglass and tissue [23,38–40]. Most light rays that strike the cone wall for the first time reflect totally, as their incidence angle is greater than the critical angle. These reflected light rays then strike the opposing wall of the cone with an incident angle lower than the critical angle, causing radial refraction of the light beam into the tissue, see Figure 2e. The device of Scheller [41] describes a unique positively polished cone-shaped fiber tip design with four slanted surfaces that split the light into four separate beams that travel in individual directions. Two devices include a design for a negatively polished tip [42,43]. This surface always contains a reflective coating that ensures that all light that strikes the cone is reflected into the tissue [42,43] or collected from the tissue [43] in radial direction.
Methods for Assessing Corneal Opacity
Published in Seminars in Ophthalmology, 2019
Thomas H. Dohlman, Jia Yin, Reza Dana
In confocal microscopy, a pinhole aperture is used to block out-of-focus light rays from reaching a detector. As only in-focus light rays are detected, higher resolution images can be obtained as compared to standard microscopy. As with OCT and Scheimpflug, these high-resolution images of the cornea can then be analyzed to quantify light scatter as an indicator of corneal opacity. This technique has been used to quantify corneal opacity in transgenic murine models of corneal haze,35 a rabbit model of photorefractive keratectomy (PRK),36 and in the clinical setting to quantify corneal haze after refractive surgery.37 The potential utility of confocal microscopy in quantifying opacity is supported by two animal studies which examined post-PRK haze and showed a strong correlation between confocal-measured light scatter and both subjective clinical opacity score38 and subepithelial scar-tissue thickness.36 However, compared to OCT and Scheimpflug, confocal image acquisition requires more time for image processing and can be uncomfortable for patients, given that it requires physical contact with the cornea. In addition, while confocal microscopes are commercially available, they are generally only found at academic medical centers.
Non-Orthogonal Corneal Astigmatism among Normal and Keratoconic Brazilian and Chinese populations
Published in Current Eye Research, 2018
Ahmed Abass, John Clamp, FangJun Bao, Renato Ambrósio, Ahmed Elsheikh
Using the axial curvature method to map corneal power in this study was based on its effectiveness in representing the overall visual acuity due to considering the optical axis as a reference in power calculations and assuming that centers of axial curvature always lay on this axis.18,37 Other mapping methods were excluded for different reasons: simulated keratometry (sim-k) for fitting a unique curvature to each power meridian38,39, the tangential curvature for its sensitivity to the digital noise associated with videokeratographers’ data and not being sensitive to optical axis position13,22 and light ray tracing for its sensitivity to numerical errors near the center of calculations at the optical axis where the corneal focal point is close to mathematical infinity.40 Because of their inherent assumptions, the simulated keratometry (sim-k) optical power method is probably least representative of corneal topography, whereas the tangential curvature method is more effective in assessing local areas of the cornea as in identifying the shape and the position of the cone in a keratoconic cornea but not in presenting an accurate global optical power estimate for the cornea. Lastly, both axial curvature and light ray tracing mapping methods are effective in representing the overall visual acuity as both consider the optical axis as a reference in the power calculations; however, the latter method was not used since the numerical analysis errors associated with it are known to be condensed in the central optic zone, where topography data is most important.41