China
Africa
Explore chapters and articles related to this topic
Describe the mechanisms of visual adaptation
Published in Nathaniel Knox Cartwright, Petros Carvounis, Short Answer Questions for the MRCOphth Part 1, 2018
Nathaniel Knox Cartwright, Petros Carvounis
Visual adaptation is the process by which the visual system automatically adjusts visual sensitivity to changes in illumination so as to extract maximum contrast from the environment. Visual sensitivity can change by 12 log units and results in changes in temporal and spatial acuity and in spectral sensitivity.
Neural adaptation to blur
Published in Pablo Artal, Handbook of Visual Optics, 2017
Michael A. Webster, Susana Marcos
Visual adaptation is one of many forms of neuroplasticity and refers to relatively rapid and temporary changes in perception when observers are exposed to a stimulus (Webster 2011). These are measured by monitoring how sensitivity or appearance is altered in the presence of an adapting stimulus, or by the lingering aftereffects when the adapting stimulus is removed. In a typical experiment, observers initially view an adapting stimulus for a short period and then make judgments about a probe stimulus (e.g., setting the contrast until it is just visible or judging its appearance such as its color, shape, or movement). The probe itself is shown briefly to avoid adapting to it and is often interleaved with reexposures or “top-ups” of the adapting stimulus to maintain a stable state of adaptation. In most cases, during or shortly after viewing the adapting pattern, the visibility of similar patterns is reduced, while patterns that are visible look different than they did before adapting, a change referred to as visual aftereffects (Thompson and Burr 2009). There are many classic examples of these aftereffects. Staring briefly at a red spot produces a greenish color afterimage; viewing a tilted line or grating causes a vertical grating to appear tilted in the opposite direction (Gibson and Radner 1937); and after watching downward motion (e.g., a waterfall), a static image appears to drift upward (Wohlgemuth 1911). As these examples illustrate, the aftereffects are typically “negative” in that a neutral stimulus (gray, vertical, or static) usually appears less like the adapting stimulus or in other words biased in the opposite direction. Yet while the form of aftereffects is similar, the neural changes giving rise to them can occur at many different levels of the visual system, beginning at the retina (e.g., for color afterimages; Zaidi et al. 2012) and cascading throughout the visual stream (e.g., with different motion aftereffects tapping different types and levels of cortical processing; Mather et al. 2008).
Positive feedback loop between vision-related anxiety and self-reported visual difficulty
Published in Ophthalmic Genetics, 2023
Lilia T. Popova, Rebhi O. Abuzaitoun, David M. Fresco, Maria Fernanda Abalem, Chris A. Andrews, David C. Musch, Joshua R. Ehrlich, K. Thiran Jayasundera
Although vision-related anxiety and disability may affect any patient with a vision condition, patients with low vision and blindness due to uncorrectable causes, including those with IRDs, are especially at risk (61–63). Because patients with uncorrectable low vision are at the end of the line for medical or surgical therapies that can alter their disease course, they depend on visual adaptation methods, assistive devices, and psychological therapies to optimize the vision they have left. These services are often offered as part of LVR, which aims to teach skills that can help patients compensate for low vision, provide patients with technology (such as magnifying devices) that can assist with their daily tasks, and connect patients to services such as psychological therapies, balance training, and home safety programs (51).
Effect of vitamin D deficiency on spatial contrast sensitivity function
Published in Clinical and Experimental Optometry, 2022
Retinal dopamine release has a circadian property that ensures visual adaptation to different lighting conditions by regulating the conduction between rods and cones. In the day time increased dopamine release causes uncoupling between rod and cone conductivity through decreasing the intracellular cyclic adenosine monophosphate level, and subsequently the protein kinase activity; this physiological sequence provides increased visual perception in bright light. On the other hand, strong electrical coupling between rods and cones occurs as a consequence of decreased dopamine release at night which can support the rod function for the detection of dim objects.19
Cognitive outcomes after cochlear implantation in older adults: A systematic review
Published in Cochlear Implants International, 2018
Annes J. Claes, Paul Van de Heyning, Annick Gilles, Vincent Van Rompaey, Griet Mertens
Ambert-Dahan et al. (2017) included 18 adults between 23 and 83 years old, with postlingual severe to profound sensorineural hearing loss. The mean duration of profound hearing loss was 6.5 (±2.1) years (range: 0.3–35 years). The participants were excluded from the study in case of neurological, psychiatric or visual illness. All entered a specific auditory-cognitive training program, which was an integral part of the routine auditory rehabilitation (Table 1, Risk of bias D). This training program was aimed at developing speech perception with the CI and cognitive abilities involved in verbal processing (e.g. attention, verbal memory, and mental flexibility). Participants’ cognition was assessed prior to and 12 months after implantation by means of 2 cognitive screening tests, the Cognitive Disorders Examination (CODEX) (Belmin et al., 2007) and the Montreal Cognitive Assessment (MoCA) (Nasreddine et al., 2005) (Appendix 3). Both tests were reported to be adapted with visual adaptation on a screen, but detailed information on the adaptation is lacking (Table 1, Risk of bias A). Furthermore, no statistical analyses were performed with respect to the change in cognitive performance (Table 1, Risk of bias C), presumably due to the small sample size and the ordinal character of the CODEX results. The qualitative analyses indicated that 4 of the 8 participants with abnormal scores before implantation, improved their cognitive performance into the normal range 12 months after implantation. On the other hand, 3 of the 10 participants with normal preoperative cognitive scores demonstrated a decrease in performance, but remained in the normal range. No control group was included or no other attempts were made to control for possible practice effects (Table 1, Risk of bias B).