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Bioengineering Aids to Reproductive Medicine
Published in Sujoy K. Guba, Bioengineering in Reproductive Medicine, 2020
In order to maintain simplicity in the design and construction most rigid endoscopes have a fixed focus. Even so the design is such that objects within a certain range of distance from the objective are fairly well focused and this range is the depth of focus. Power of accommodation of the eye also helps in viewing objects at varying distances and the accommodation increases the range beyond the intrinsic depth of focus of the instrument. An older observer with reduced power of accommodation will obviously be able to clearly see objects over a smaller range of distance than a younger endoscopist with normal amplitude of accommodation which usually ranges from infinity to 25 cm in front of the eye. The difference between the intrinsic depth of focus of an endoscope and the effective range of focus as viewed by an observer has important bearing in photography through an endoscope. An observer may see an object clearly through an endoscope but the picture taken may come out as blurred. This may be because the observer has exerted his power of accommodation to bring the object into focus whereas the camera obviously does not have this provision. Modern endoscopic cameras are provided with focusing arrangement which is independent of the power of accommodation of the photographer’s eye.
The Illumination
Published in William C. Beck, Ralph H. Meyer, The Health Care Environment: The User’s Viewpoint, 2019
The general room illumination should be controllable and should provide a uniform 2200 lux (200 fc), from recessed luminaires. Luminance ratios should be no greater than 5:1 within view of the surgeon and his team. The surgical task lighting system should provide at least 27 kilolux (2500 fc) at the center of a field at least 10 in. in diameter, with at least one fifth this much at the periphery of the pattern. The source should be so arranged that a minimum shadow will be created by the surgeon and his team at the depth of the wound. The depth of focus should be at least 15 centimeters.
Physics
Published in Peter R Hoskins, Kevin Martin, Abigail Thrush, Diagnostic Ultrasound, 2019
Kevin Martin, Kumar V Ramnarine
This equation shows that the depth of focus increases rapidly with increases in f-number. Doubling the f-number gives a fourfold increase in depth of focus. Depth of focus also increases with the wavelength. The equation predicts depths of focus of 32 and 14 mm, respectively, for the beams in Figure 2.22a and b.
Polychromatic through-focus image quality in a wavefront-shaping presbyopia correcting intraocular lens
Published in Expert Review of Ophthalmology, 2022
Francisco Pastor-Pascual, Alicia Gómez-Gómez, Robert Montés-Micó, Ramón Ruiz-Mesa, Pedro Tañá-Rivero
Some clinical studies have been published showing the visual performance of patients implanted with several EDOF IOLs [3], and, in addition, in vitro studies [4–10], carried out with an optical bench, have also shown different optical properties of these lenses compared with other IOLs. Other studies have aimed to measure the optical quality of eyes implanted with EDOF IOLs in order to understand the optical quality of the eye when implanted with these lenses. In vivo optical quality measurement of eyes with an EDOF has been done using ray-tracing [11–15], Hartmann-Shack [16], skyascopy [17–19] or double-pass [20] techniques. It has been proposed several objective metrics for predicting refraction from wavefront aberrations being a useful method to compute the depth of focus (DoF) from the wavefront aberration map [21–23]. Despite this, most of the studies do far of the optical quality performances of EDOF has been done assuming monochromatic light, that is neglecting the effects of chromatic performance of the IOL on the retinal image. It is possible to use objective metrics of image quality applied to wavefront aberrations in infrared light to accurately predict subjective refractive error for polychromatic light [24,25]. However, although the retinal image is typically polychromatic no studies have examined polychromatic through-focus image quality in eyes implanted with EDOF IOLs.
Effect of Pupil Size and Binocular Viewing on Accommodative Gain in Emmetropia and Myopia
Published in Journal of Binocular Vision and Ocular Motility, 2020
Chun Tang Huang, Tsukasa Satou, Takahiro Niida
As mentioned previously, AG with stimuli from 3D to 5D was around 70%, with little variation. However, there were small but significant differences in AG among different conditions. AG in the translucent condition in the myopia group was significantly lower than in the monocular condition, whereas there was no difference between these conditions in the emmetropia group. Both monocular and translucent conditions were with monocular viewing, with the difference between them being pupil size. The difference in AG between these conditions may be attributed to pupil size. Nakatsuka et al. reported that myopic children showed poor accommodative responses to near-distance targets and large lags of accommodation when their refractive error was fully corrected under binocular viewing conditions,12 a conclusion that our results support. Collins et al. discussed that higher-order aberrations in myopic eyes were larger than in emmetropic eyes, which increase the depth of focus.13 Pupil contraction induces an increase in the depth of focus and decreases higher-order aberrations.14 Thus, the effect of pupil contraction further promotes an increase in the depth of focus in myopic eyes. In addition, Rosenfield et al. demonstrated that myopic eyes were less sensitive to the presence of blur.5 An increase in the depth of focus with pupil contraction may lead to induction of minimal accommodation in myopic eyes. Therefore, the effect of pupil size may contribute largely to the decrease in accommodative accuracy in myopic eyes with binocular viewing.
Cardiovascular rEmodelling in living kidNey donorS with reduced glomerular filtration rate: rationale and design of the CENS study
Published in Blood Pressure, 2020
Kjersti Benedicte Blom, Kaja Knudsen Bergo, Emil Knut Stenersen Espe, Vigdis Rosseland, Ole Jørgen Grøtta, Geir Mjøen, Anders Åsberg, Stein Bergan, Helga Sanner, Tone Kristin Bergersen, Reidar Bjørnerheim, Morten Skauby, Ingebjørg Seljeflot, Bård Waldum-Grevbo, Dag Olav Dahle, Ivar Sjaastad, Jon Arne Birkeland
Non-occlusive atherosclerotic plaques and increased carotid intima media thickness represent early vascular remodelling and is associated with increased cardiovascular risk [52]. Carotid intima media thickness will be measured after recommendations by Touboul et al. [53]. Carotid ultrasound in B-mode will be used, with a (6–15.0 MHz) linear array transducer (ML6-15-D) at frequencies >7 MHz. The depth of focus will be about 30–40 mm and the optimal frame rate about 25 Hz (>15 Hz). The common carotid artery, the carotid bulb and the internal carotid artery will be visualised on both sides in longitudinal and cross-sectional views. The carotid intima media thickness measurement will be performed with a lateral probe position on both sides in a longitudinal view, perpendicular to the ultrasound beam with both walls clearly visualised in a region free of plaques on the far wall of the common carotid artery, at least 5 mm below its end. An automated system will be used to provide accurate measurements of carotid intima media thickness and common carotid artery inter-adventitial and intraluminal diameters.