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Telescopes for Inner Space: Fiber Optics and Endoscopes
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
Optics can be divided into two branches: geometrical optics and wave optics. Geometrical (or ray) optics describes how light travels within various materials, how it interacts with matter, and how light can be manipulated to perform various useful functions. Geometrical optics assumes that within a uniform medium, light travels (or propagates) along straight lines from its source to a distant point (Figure 2.3a). By medium, we mean any material, such as air, water, glass, blood, fat, or other human tissue. The straight lines along which light propagates are called light rays, or simply rays. A narrow shaft of sunlight breaking through a cloud, or a laser beam, are good approximations to a ray of light. In this chapter we will see that to draw rays we use the properties of parallel lines, angles, and other geometrical figures, hence the term geometrical optics. Wave optics, discussed in the next chapter, builds on the fact that light is an electromagnetic wave carrying energy through vacuum or matter. This alternative approach allows us to understand a wider variety of optical phenomena relevant to medical applications.
EM behavior when the wavelength is much smaller than the object
Published in James R. Nagel, Cynthia M. Furse, Douglas A. Christensen, Carl H. Durney, Basic Introduction to Bioelectromagnetics, 2018
James R. Nagel, Cynthia M. Furse, Douglas A. Christensen, Carl H. Durney
In-between these extremes are the optical waves, which by most definitions encompass the infrared, visible, and UV regions. These waves are the main focus of this chapter. They share many common features and play an important role in human life. Since their wavelengths (from one-tenth to a few micrometers) are much smaller than the typical object, it is often convenient to describe them in two ways that are different from those used in the previous chapters. The first difference is that diffraction is often unnoticeable for these waves (unless purposely caused by specialized diffraction gratings or other very small structures). This is because, as covered in Section 3.8, the degree of diffraction is proportional to the ratio of wavelength to object size. Since the wavelength is short compared to most objects (for example, a mirror), diffraction is small and does not play a major role in the behavior of the propagating wave. The waves then can be conveniently described by straight-line ray propagation, and ray tracing is used to make optical propagation much easier to visualize and determine. This is the domain of geometrical optics, where the rays follow geometrical rules. Ray tracing is used extensively in the first half of this chapter.
Evaluating the blue-light hazard from solid state lighting
Published in International Journal of Occupational Safety and Ergonomics, 2019
John D. Bullough, Andrew Bierman, Mark S. Rea
The physical characteristics of the eye, including its approximately spherical shape, a round pupil opening formed by the iris and an adjustable lens, enable it to function as a precise imaging device. Light incident on the pupil opening is focused on the retina, where it forms an irradiance distribution corresponding to the radiance of the scene outside the eye. Using geometrical optics and radiometry principles, and ignoring absorption and scattering in the eye for the moment, the following equation can be derived [54]: Eretina= retinal irradiance; L= radiance being focused; Apupil= area of the pupil opening; feye= focal length of the eye, roughly 1.7 cm. As stated previously, Eretina is the irradiance at a point on the retina, not an average, and the corresponding radiance is for a specific viewing direction which, e.g., can be a small light source in the field of view.
From monocular photograph to angle lambda: A new clinical approach for quantitative assessment
Published in Journal of Binocular Vision and Ocular Motility, 2022
Maxence Rateaux, Dominique Bremond-Gignac, Matthieu P. Robert
Figure 1 represents the geometrical optics of the anterior chamber. In this analysis, we assume that the distance between V and C is negligible and therefore that value of angle λ, which corresponds to the angle V’ is the orthogonal projection of
The usefulness of optics-based courses for optometry and vision science alumni: a cross-sectional online survey
Published in Annals of Medicine, 2022
Mohammad A. Alebrahim, May M. Bakkar
Optometry curricula worldwide include medical sciences courses (e.g. pathology, neuroscience, and microbiology) and courses related to optics [7–10]. Optics is a branch of physics that deals with studying the properties of light and its behaviour, such as interaction with matter, reflection, refraction, interference, diffraction, and polarisation [11,12]. Optics courses in the optometry curriculum aim to provide students with primary knowledge of two main fields, geometrical optics and visual optics, which form the basis for ocular physiology, contact lenses, low vision, and ophthalmic instrumentation [13–19].