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Congenital Cranial Dysinnervation Disorder
Published in Vivek Lal, A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
Correction of refractive error is an essential component of non-surgical management of DRS, and treatment of amblyopia should be initiated where possible. To decide for surgical correction, the following points should be assessed prior: Deviation in primary positionQuantification of limitation of abductionThe severity of globe retractionOvershoots present in adduction
Refractive Errors, Myopia, and Presbyopia
Published in Ching-Yu Cheng, Tien Yin Wong, Ophthalmic Epidemiology, 2022
Ka Wai Kam, Chi Pui Pang, Jason C. S. Yam
Refractive errors are a group of ophthalmic disorders that individually or in combination affect individuals of all ages and ethnicities in both sexes. When the optical system in an eye fails to bring incoming light into focus on the retina, the resultant image perceived by the individual becomes blurred. Refractive errors can be classified into three main types: myopia, astigmatism, and hyperopia. There is also presbyopia, which literally means aging vision, and affects people at a later stage in life, usually in the fifth decade. It is sometimes included as a fourth type of refractive error, although it may be regarded not as an error of refraction because it is due to the loss of accommodation by the lens.
Objective and Camera Lenses
Published in Robert J. Parelli, Principles of Fluoroscopic Image Intensification and Television Systems, 2020
In a simple lens, focal length is usually of most importance. This is a characteristic of all lenses and is generally used to identify a lens since it is a measure of the refracting power of the lens. Refraction is defined as the bending of a beam of light energy when it passes across an interface of materials with different indices of refraction. Focal length is simply the distance measured from the lens to a focal point. The focal point is, by definition, that point at which light incident upon a lens from an infinitely distant object is brought to a focus. The importance of focal length lies in the fact that this is the determining factor in the magnification at which a scene is an image on the television camera tube. Lens characteristics are shown in Figure 2.2
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
Refraction is defined as the change in direction of a transmitted light beam after it enters a second medium. Reflection is defined as the change in direction of a light beam at an interface that returns the light beam back to the original medium. The angle of incidence of the light beam on the surface and the material properties of the two media determine the intensity and direction of the refracted and reflected light beam. Another way to steer light is scattering: multiple changes in refractive index force the light beam to randomly change direction in a series of reflection events, resulting in diffuse light scattering. Lastly, a fundamentally different method to steer a light beam is diffraction. Diffraction is defined as the bending of light after encountering a small opening or obstacle. The light beam does not bend in one direction; instead, a diffraction pattern is generated by the interference of different wave fronts. Diffraction is predominant for apertures and obstacles with sizes in the range of the wavelength of the incident light.
Instant vision assessment device for measuring refraction in low vision
Published in Clinical and Experimental Optometry, 2021
Refraction is an essential part of eye care because it determines the refractive error of an eye and its corrections by optical devices to achieve the best possible visual acuity. However, low vision refraction is often overlooked once there is a measured decrease in visual acuity based on a pathology.2 Consequently, the best-corrected visual acuity is not always determined or verified. In fact, refraction often can measurably improve visual acuity, which, at the very least, can modify the magnification needed to enhance visual acuity, and, at best, eliminates the need for magnification devices altogether.2 The benefits of refraction in low vision have been documented and shown to significantly improve visual acuity by two lines or more in 11% of low vision patients.3
Neuro-Ophthalmic Literature Review
Published in Neuro-Ophthalmology, 2018
David Bellows, Noel Chan, John Chen, Hui-Chen Cheng, Peter MacIntosh, John H. Pula, Michael Vaphiades, Konrad P. Weber, Sui Wong
Noonan syndrome (NS) is an autosomal dominant disorder with variable phenotype, including short stature, congenital heart defects, and ophthalmological abnormalities. Different mutations in coding genes leading to dysregulation of the Ras/mitogen-activated protein kinase pathway can cause NS. The authors describe a retrospective review of 105 NS patients in the Netherlands. Sixty eight were under the age of 18 years. The primary outcome of the study was presence of ocular abnormalities in NS population. Seven patients were visually impaired, mainly attributable to binocular optic nerve abnormalities and manifest nystagmus related to RAF1, SHOC2, and KRAS gene mutations. Twenty-eight patients had amblyopia. Refractive errors included myopia, hyperopia, and astigmatism. Ten patients had high refractive errors.