China
Africa
Explore chapters and articles related to this topic
An Approach to Visual Loss in a Child
Published in Vivek Lal, A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
Muhammad Hassaan Ali, Stacy L. Pineles
A preference to view objects of regard at very close range is seen occasionally in normal children, reflecting a transient behavioral pattern. Children with poor vision often do so consistently to produce linear magnification (by shortening the focal length), to damp an existing nystagmus with convergence to improve vision or, in the case of uncorrected aphakic children, to induce a miotic response to increase depth of focus and create a pinhole effect. Visual function may also be qualitatively evaluated with the optokinetic reflex. When the visual field moves with respect to the eyes, as with a rotating optokinetic drum, the eyes track the moving field to the limit of their excursion and then make a recovery saccade in the opposite direction and so on, producing optokinetic nystagmus. Cortically blind patients cannot generate optokinetic nystagmus (9).
Smart Eye Tracking Sensors Based on Pixel-Level Image Processing Circuits
Published in Iniewski Krzysztof, Integrated Microsystems, 2017
The optokinetic reflex is a visually guided reflex, the purpose of which is to compensate for body and head movements so that retinal image motion is minimized. The optokinetic reflex responds optimally if the stimulus is movement of all, or a large portion of, the retinal image. We have no voluntary control over these reflexive eye movements. If the retinal image of the whole field of view moves, our eyes invariably follow this motion. Just as in the case of pursuit movements, the kinematics of eye movements resulting from the optokinetic reflex are determined by the motion of the stimulus.
Sparse classification of discriminant nystagmus features using combined video-oculography tests and pupil tracking for common vestibular disorder recognition
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2020
Aymen Mouelhi, Amine Ben Slama, Jihene Marrakchi, Hedi Trabelsi, Mounir Sayadi, Salam Labidi
Vertigo is caused by various kinds of vestibular pathology that affects the functionality of the eye and head movements. It causes disequilibrium by a unilateral reflectivity of the vestibule (Lin et al. 2005; Donnard et al. 2015). The measurement of abnormal eye movement is related to vestibular ocular channel, which is stimulated by different tests such as kinetic and caloric experiments. The kinetic test (KT) or rotational chair testing is a stimulus of semicircular canal (SCC) couple. It allows an evaluation of the highest slow phase velocity (SPV) value from the post-rotatory nystagmus. Meanwhile, caloric test (CT) is exclusively able to explore and evaluate each horizontal SCC separately. It is applied to calculate the reflectivity between the right and left ears by collecting the cumulative of nystagmus slow velocities after the irrigation of inner ear with cold and warm water during 20 seconds. In addition, the head-shaking test (HST) provides an exploration of both peripheral and central vestibular functions at high frequency (2 Hz) (Van Beuzekom and Van Gisbergen 2002; Faucheux et al. 2006; Kim et al. 2012; Santos et al. 2018). Clinicians shake the head of the patient at a frequency of 2 Hz for 20 seconds with a rotation on both sides of 45 degrees. Eye movements are recorded for 1 minute to evaluate for post-rotary nystagmus. In Saccadic test (ST) or known also as optokinetic nystagmus testing, visual targets move from left to right or from right to left and the patient must look straight ahead and follow the target with his or her eyes. The movement of the visual target produces the optokinetic reflex. In central pathologies such as stroke, the patient’s optokinetic reflex gain is reduced.
Clinical testing of mild traumatic brain injury using computerised eye-tracking tests
Published in Clinical and Experimental Optometry, 2022
Alice Cade, Philip RK Turnbull
The optokinetic reflex aims to stabilise retinal slip across a wide portion of the retina,84 and consists of two distinct components – a slow phase in the direction consistent with the optic flow, and a fast-phase saccadic movement in the opposite direction.85 A common example of the optokinetic reflex are eye movements that occur when watching passing telephone poles from a moving car or train.