Visual impairments
Michael Horvat, Ronald V. Croce, Caterina Pesce, Ashley Fallaize in Developmental and Adapted Physical Education, 2019
In addition to visual acuity, vision undergoes a developmental process that allows the child to use vision for reading as well as using visual information for learning. In the newborn, the muscles of the eye are weak, and vision is limited to focusing on near objects and responses to light. It could be said that we are born with sight but not vision. Vision will develop from several functions of the eye. For example, visual acuity is the ability to see objects clearly, as measured by performance on the Snellen test. In addition, the eyes must also demonstrate visual fixation, that is, the ability to gaze directly at an object, and pursuant fixation, by which they follow a moving object. Fixation of an object is pursuit at zero velocity, with the pursuit system correcting for small drifts off target. These movements are slower than the fast saccadic movements (involuntary, abrupt, small movements, such as those made when the eye changes their point of fixation). The slower eye movements go by a variety of names but are most commonly called smooth pursuit or tracking movement. The brain must allow the ability to process information and slowly track the object.
Sensory Development and Motor Control in Infants and Children
Mark De Ste Croix, Thomas Korff in Paediatric Biomechanics and Motor Control, 2013
The eye also contains a set of six extraocular muscles (Figure 2.1b), which can move the eye vertically, horizontally and torsionally (Aslin 1987). When looking directly at an object, the visual image falls on the fovea, which is a small area of the retina containing only cones. Both head and body muscles can be used to foveate, but for rapid foveation the extraocular muscles are needed. They are also used for slow pursuit tracking of objects. In smooth pursuit tracking, the eyes can match the velocity of the moving stimulus. The extraocular muscles are also needed for binocular fixation, that is, moving both eyes to look directly at an object. The lack of binocular fixation can produce a double image (diplopia) or result in a loss of binocular depth perception or stereopsis (Aslin 1987).
Can Cognitive Theories Help to Understand Motor Dysfunction in Autism Spectrum Disorder?
Elizabeth B. Torres, Caroline Whyatt in Autism, 2017
Eye movements serve to maintain objects of interest on the fovea, the region of the retina that provides the greatest acuity and color detection (Leigh and Zee 2015). Accurate eye movements are essential for on-line regulation of fine and gross motor accuracy, in addition to proprioceptive signals, and also for providing visual feedback to refine movement accuracy over the long term. Saccades are semiballistic eye movements that shift the eye toward an object of interest, while smooth pursuit eye movements help us to track moving objects, while either an object or ourselves (or both) are in motion (Leigh and Zee 2015). These two main types of eye movements help us to plan actions and coordinate our whole-body movements, and give us visual information about our changing environment to enable us to adapt our actions on the fly. There are a number of known visual processing and ocular motor disturbances in ASD that are likely to impact these processes, which include impaired motion detection (Manning et al. 2013; Takarae et al. 2014), inaccurate eye movements (Takarae et al. 2004a, 2004b; Johnson et al. 2012; Schmitt et al. 2014), and inefficient timing of ocular motor with fine motor actions (Crippa et al. 2013).
The Effect of Target Velocity on the Fast Corrective Response during Reaching Movement
Published in Journal of Motor Behavior, 2022
Kosuke Numasawa, Tomohiro Kizuka, Seiji Ono
In our experiment, participants were required to track the target motion, unlike the MFR. When we look at a small moving object, smooth pursuit eye movements are used to hold the target image on the fovea (Krauzlis, 2004; Lisberger, 2010; Ono, 2015). Smooth pursuit eye movements are driven by retinal slip signals generated from the difference between actual target motion and eye velocity. In particular, retinal slip information carried in the MT/MST plays an important role in the initial part of smooth pursuit (Dursteler & Wurtz, 1988; Newsome et al., 1985). As mentioned above, since arm movements responding to visual motion are associated with neuronal activity in the MT/MST, we speculate that the fast corrective response shares the same visual motion processing as smooth pursuit eye movements. Indeed, our results indicate that the initial amplitude (first 50 ms) of the corrective response increases according to the target velocity. However, a previous study has reported that the initial part of smooth pursuit (open-loop period) is not dependent on target velocity (Lisberger & Westbrook, 1985). Thus, one possible explanation is that the initiation of arm movement is generated differently from the eye movement, even though they both share a common retinal slip signal. Indeed, Saijo et al. (2005) have suggested that the MFR and the eye movements elicited by the large-field visual motion are separated even they are processed by the same visual information in parallel (Saijo et al., 2005).
Scene through the eyes of an apex predator: a comparative analysis of the shark visual system
Published in Clinical and Experimental Optometry, 2018
Shaun P Collin
Eye movements in sharks are thought to be controlled through efference copy, a neural mechanism in which a copy of the signal that controls the body movements during swimming is transmitted to the extraocular muscles, inducing eye movements that counteract body rotation.1965 Compensatory eye movements keep the retinal image stable when the animal is moving or when the visual world is moving around the animal.1965 Smooth pursuit eye movements allow the eyes to track moving objects with their retinal areas of high resolution.1970 Both compensatory and smooth pursuit eye movements would be expected in sharks as a way of keeping the image of the visual world stable on the retina as the animal moves through its environment.1942 Unfortunately, little is known about these types of eye movements in free‐swimming sharks.
Eye Movement Abnormalities in Amyotrophic Lateral Sclerosis in a Tunisian Cohort
Published in Neuro-Ophthalmology, 2022
Arwa Rekik, Saloua Mrabet, Imen Kacem, Amina Nasri, Mouna Ben Djebara, Amina Gargouri, Riadh Gouider
Altered horizontal smooth pursuits were the most common eye movement abnormality among our patients. However, results do diverge when it comes to studying smooth pursuits in ALS patients. For example, Shaunak and collaborators found that smooth pursuits were normal in all of the 17 patients involved in their study.22 Gizzi and co-authors found them altered, but only in patients who had associated Parkinsonism.18 Recent studies conducted on the Korean population by Kang et al. found, similar to our study that altered horizontal pursuits were the main abnormality (64% of cases).19 Smooth pursuit eye movements are generated through the cerebro-ponto-cerebellar pathway. Cortical regions are considered as the generators of the pursuit movement with the pons being the final destination. The frontal lobe is implicated via the frontal eye fields (FEF), which encode and predict the pursuit trajectories.23,24 These anatomical data explain the established correlations of altered smooth pursuits with the presence of non-motor signs in general and specifically with bladder dysfunction and executive impairment. Such a combination may not be so surprising since both executive and bladder dysfunction are consistent with frontal lobe pathology.
Related Knowledge Centers
- Eye
- Eye Movement
- Eye Tracking
- Fixation
- Saccade
- Psychophysics
- Vision Science
- Gaze
- Vestibulo–Ocular Reflex
- Search Coil Magnetometer