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Special Considerations in Gaze
Published in Vivek Lal, A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
Mohamed Elkasaby, Aasef G. Shaikh
The cerebral cortex executes the visually guided saccades, and the commands are carried in two distinct pathways that converge onto the superior colliculus [1, 2]. The frontal eye field (FEF), supplementary eye field (SEF) and dorsolateral prefrontal cortex (dlPFC) comprise the first pathway. The saccade signals generated in this pathway are projected to the caudate nucleus [3–6]. The caudate directly inhibits the substantia nigra pars reticulata (SNpr) [6, 7]. Inhibition of the latter activates the superior colliculus via removal of tonic GABAergic inhibition [8–11]. The cessation of tectal inhibition initiates saccades. The parietal eye field (PEF) comprises the second pathway [1, 2]. The PEF has reciprocal connections with the FEF and it also provides input to the superior colliculus [12, 13]. The connections between the PEF and FEF participate in visual processing, while those between PEF and superior colliculus seem to affect saccade expression. The cortical lesions typically do not influence the kinematic properties of saccades, but their planning (amplitude and timing matrix) are affected [14, 15].
Dementia
Published in Henry J. Woodford, Essential Geriatrics, 2022
The physical examination should incorporate the features of a general medical assessment, in particular looking for signs of neurological and vascular disease. Speech will have been assessed as part of the mental state examination. Cranial nerves may show reduced up and down gaze with progressive supranuclear palsy (PSP) (see page 188). Impaired saccadic eye movements may provide more subtle signs of an underlying movement disorder (seeFigure 9.5). Pyramidal tract or cerebellar signs may indicate VaD. Increased tone, tremor and bradykinesia suggest an underlying movement disorder but be aware of paratonia (see page 169).
Neurologic Diagnosis
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
Saccades are rapid eye movements to an eccentric target tested by getting the patient to look rapidly from side to side and up and down or rapidly to an eccentric target. Look at initiation, velocity, and accuracy of the eye movement. In some diseases, saccades may be abnormal early while pursuit is normal (e.g. in progressive supranuclear palsy). Saccades can be used to accentuate a mild limitation of eye movement to make it easier to see (e.g. in an abduction defect).
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
With regard to eye movements, a target jump stimulus induces saccades while a target motion stimulus induces smooth pursuit. Although both eye movements play an important role in holding the visual image on the fovea, these are driven by different visual information. Saccades are driven by the retinal position error between eye and target position (Krauzlis et al., 2000), whereas smooth pursuit is driven by the retinal velocity error (retinal slip) between eye and target motion (Krauzlis, 2004; Lisberger, 2010; Ono, 2015). Furthermore, these eye movements have different latencies, as saccade latency is about 150-200 ms (Leigh & Zee, 2015) while pursuit latency is about 120-140 ms in human subjects (Krauzlis et al., 1999; Lindner & Ilg, 2000; Miyamoto et al., 2020). Since these eye movements are based on different control systems, the fast corrective response to the target motion may have different properties from the response to the target jump.
Evaluation of saccadic velocity in patients with orbital floor fracture before and after surgery
Published in Seminars in Ophthalmology, 2022
Ken Kakeue, Masanobu Kanazawa, Tatsuya Yunoki, Miharu Mihara, Atsushi Hayashi
Saccades play an important role in the rapid movement of eyes to visual targets. The saccadic PV is reported to be an important parameter for saccadic evaluation,18,19 and the examination of the saccadic PV using an eye tracking system can measure dynamic ocular motility. However, to the best of our knowledge, there are no reports of a detailed evaluation of saccades before and after surgery in patients with orbital floor fractures. In the present patient series, the non-injured eyes did not show any significant difference in saccadic PV between before and after surgery. On the other hand, in the injured eyes, there was no significant difference in downgaze, adduction, or abduction, but improvement was observed in upgaze vision. We believe that saccade PVs may be a useful method of assessing eye movements in patients with orbital floor fracture. Additional studies are needed to evaluate the usefulness of the measurement of saccade PVs.
Impact of Alzheimer’s Disease in Ocular Motility and Visual Perception: A Narrative Review
Published in Seminars in Ophthalmology, 2022
Deterioration of fixation and saccadic eye movements in patients with AD may have a negative impact on the performance of everyday activities.13 In this bibliographic review, most of the authors show that ocular movements are affected in AD, presenting larger and more frequent saccades, with interruption of tracking at low object speeds,72,75 generation of intense saccades, loss of attention and increased blinking.74 Two of the factors that can contribute to this increase of saccades are the perceptual deficits that are present and attentional problems.67 Regarding the fixation pattern in AD, the intrusive saccades evaluated at the start of a longitudinal study in AD patients increased during a 18-month follow-up, whereas a control group remained at the same levels measured at the baseline.29 This saccadic alteration in AD was associated with a greater latency in tracking.29 When measuring the reaction time in the initial stage, AD patients were found to be slower, whereas at 12 months of follow-up both AD and control group subjects displayed more rapid reductions in the reaction to the gap vs overlapping.29