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An Approach to Oculomotor Anomalies in a Child
Published in Vivek Lal, A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
The oculomotor nucleus resides in the midbrain and is divided into individual subnuclei for each extraocular muscle. Interestingly, the SR subnucleus innervates the contralateral SR muscle, while the remainder of the subnuclei innervates the ipsilateral corresponding muscles. The Edinger-Westphal nucleus, which supplies innervation to the pupillary constrictors, is shared by both sides. The oculomotor nerve fascicle exits the brainstem through the ventral midbrain in the interpeduncular fossa.
Cranial nerves
Published in Ibrahim Natalwala, Ammar Natalwala, E Glucksman, MCQs in Neurology and Neurosurgery for Medical Students, 2022
Ibrahim Natalwala, Ammar Natalwala, E Glucksman
Regarding clinical abnormalities of the pupils, which of the following are true and which are false? Horner’s syndrome is caused by a lesion to the parasympathetic pathway and causes a unilateral constricted pupil with associated ptosis.In a relative afferent pupillary defect (RAPD), the consensual light reflex is weaker than the direct light reflex.Argyll Robertson pupils are small, accommodate to near objects but are unreactive to light.Denervation of the ciliary ganglion can lead to a dilated pupil that reacts slowly to bright light.The Edinger-Westphal nucleus responsible for pupillary constriction is located in the midbrain at the level of the superior cerebellar peduncle.
Miscellaneous
Published in Bobby Krishnachetty, Abdul Syed, Harriet Scott, Applied Anatomy for the FRCA, 2020
Bobby Krishnachetty, Abdul Syed, Harriet Scott
Light is shone into the eye which enters the pupil and stimulates the retina. Afferent limb: retinal ganglion cells transmit the light signal to the optic nerve and the action potential travels along the axon. The optic nerve enters the optic chiasma where the nasal retinal fibres cross to contralateral optic tract and the temporal retinal fibres stay in the ipsilateral optic tract.Centre: fibres from the optic tracts project and synapse in the pretectal nuclei in the dorsal midbrain. The pretectal nuclei project fibres to the Edinger-Westphal nuclei bilaterally (therefore responsible for the direct and consensual response to light) via the posterior commissure.Efferent limb: the Edinger-Westphal nucleus projects preganglionic parasympathetic fibres, which travel along the oculomotor nerve and then synapse with the ciliary ganglion, which sends postganglionic parasympathetic fibres (short ciliary nerves) to innervate the sphincter muscle of the pupils resulting in pupillary constriction.
Contrast Acuity and the King-Devick Test in Huntington’s Disease
Published in Neuro-Ophthalmology, 2020
Ali G. Hamedani, Tanya Bardakjian, Laura J. Balcer, Pedro Gonzalez-Alegre
The pupillary light reflex is a polysynaptic reflex arc that involves retinal photoreceptor activation and ganglion cell depolarisation; conduction through the optic nerve, chiasm, and tract; signalling across the pretectum to the Edinger-Westphal nucleus; and pupillary constriction via the third cranial nerve. Consequently, it can be affected by abnormalities at either the afferent or efferent level. In both symptomatic and presymptomatic patients with autosomal dominant Alzheimer’s disease, subtle differences in pupillary light reflex have been identified19, consistent with the cholinergic deficit observed in that disease. We did not observe any differences in pupillary function in HD, which may help to explain why the benefit from cholinesterase inhibitors for cognitive function or chorea in HD has been minimal.32 Because pupillometry was performed under scotopic (dark-adapted) conditions using mixed-wavelength white light, afferent activation was driven primarily by rod photoreceptors, and subtle cone or intrinsically photosensitive retinal ganglion cell dysfunction may not have been captured using this method. Future studies of pupillometry in HD would benefit from both photopic (light-adapted) and scotopic testing at different ranges of light wavelength.
Amplitude of Accommodation in Patients with Multiple Sclerosis
Published in Current Eye Research, 2019
Bekir Küçük, Mehmet Hamamcı, Seray Aslan Bayhan, Hasan Ali Bayhan, Levent Ertuğrul Inan
When the target distance is changed, the lens power must be altered to clearly view it; this is known as ocular accommodation.25 The accommodation reflex starts in the retinal ganglion cells with the light reflex. These impulses are sent through the optic nerve, the optic chiasma, and the optic tract. Most optic tract fibers go to the pretectal area, although some fibers synapse with the second-order neurons in the lateral geniculate nucleus of the thalamus. Then, second-order neurons carry the impulses through the optic radiation to the visual cortex. Impulses pass from the visual cortex to the prefrontal cortex, and fibers pass through the internal capsule to reach the midbrain. Then, the fibers in the midbrain synapse with the oculomotor nucleus and the Edinger-Westphal nucleus.26 The motor fibers are carried by the oculomotor nerve from the oculomotor nucleus to the medial rectus muscle, where both eyes converge. The efferent fibers of the Edinger-Westphal nucleus (which is the parasympathetic autonomic nucleus) accompany the oculomotor nerve and synapse in the ciliary ganglion. Then, the postganglionic fibers of the ciliary ganglion pass the short ciliary nerves to supply the sphincter pupillae muscle and the ciliary muscle, which allows the lens to thicken27 (Figure 1). This mechanism is controlled by the autonomic nervous system.23
Don’t Miss This! Red Flags in the Pediatric Eye Exam: Pupils
Published in Journal of Binocular Vision and Ocular Motility, 2019
Jennifer E. Lambert, Stephen P. Christiansen, Crandall E. Peeler
The pupillary finding in dorsal midbrain syndrome is light-near dissociation. The optic nerves carry a light stimulus to the optic chiasm, where axons decussate. Before reaching the lateral geniculate nucleus, some light-carrying axons leave the optic tract and enter the superior colliculus at the level of the midbrain. These signals synapse at the pretectal nucleus. The pretectal nucleus projects to the Edinger–Westphal nucleus, from which the parasympathetic fibers to the pupil arise. Light-near dissociation occurs when the pupillary fibers are injured entering the Edinger–Westphal nucleus caudally, which spares the accommodative fibers.5 The pupils, therefore, respond briskly to accommodation (near) but sluggishly to light.