neuro-opthamology Flashcards
(86 cards)
what makes CNII
formed by the convergence of retinal ganglion cell axons
what are the four parts of CNII optic/nerve
- Intraocular (shortest; 1 mm): Exits posteriorly via the lamina cribrosa (scleral opening).
- Intraorbital (longest; 25 mm): Has myelinated covering. Ends at the optic foramen.
- Intracanalicular: Where the optic nerve exits the orbit through the optic canal to enter the middle cranial fossa.
- Intracranial: Ends at the optic chiasm.
CNII blood supply
● Intraocular: Short posterior ciliary artery.
● Intraorbital to intracranial: Pial vessels of ophthalmic artery.
location of chiasm
anterior to the hypothalamus and usually directly superior to the pituitary gland.
what is junctional scotoma
anterior chiasmal lesions
ipsilateral optic neuropathy with contralateral superotemporal defects.
A few photosensitive retinal ganglion cell axons connect with the suprachiasmatic nucleus of the hypothalamus. This is important for the body’s circadian rhythm.
what is the optic tract
connect the optic chiasm with the lateral geniculate nuclei (LGN). The optic tract conveys signals from the contralateral nasal retina and the ipsilateral temporal retina.
Where is the oculomotor nerve based
dorsal midbrain at the level of the superior colliculus
motor functions of the oculomotor nerve
● Ipsilateral innervation to IO, IR and MR.
● Contralateral innervation to SR.
● Bilateral innervation to levator muscle.
pathway of oculomotor nerve
CNIII exits the brainstem through the interpeduncular fossa, passing between the posterior cerebral artery and superior cerebellar artery. Along its path, it travels near the uncus of the temporal lobe, making it vulnerable for compression in cases of uncal herniations. It then travels through the lateral wall of the cavernous sinus superior to CNIV and bifurcates into a superior and inferior branch at the anterior aspect of the sinus.
It enters the orbit through the SOF within the annulus of Zinn. The superior branch innervates the SR and the levator muscle, while the inferior branch innervates the MR, IR and IO.
CNIII is accompanied by parasympathetic fibres originating from the Edinger- Westphal nuclei, located in the midbrain dorsal to oculomotor nuclei, which innervates the sphincter papillae and ciliary body muscles.
pathway of oculomotor nerve
CNIII exits the brainstem through the interpeduncular fossa, passing between the posterior cerebral artery and superior cerebellar artery. Along its path, it travels near the uncus of the temporal lobe, making it vulnerable for compression in cases of uncal herniations. It then travels through the lateral wall of the cavernous sinus superior to CNIV and bifurcates into a superior and inferior branch at the anterior aspect of the sinus.
It enters the orbit through the SOF within the annulus of Zinn. The superior branch innervates the SR and the levator muscle, while the inferior branch innervates the MR, IR and IO.
CNIII is accompanied by parasympathetic fibres originating from the Edinger- Westphal nuclei, located in the midbrain dorsal to oculomotor nuclei, which innervates the sphincter papillae and ciliary body muscles.
pathway of the pupillary light reflex
The fibres involved in the pupillary pathway originate from the retinal ganglion cells. Those fibres exit the optic tract before reaching the LGN and enter the midbrain to synapse on the ipsilateral pretectal nucleus. The pretectal nuclei project bilateral fibres to the contralateral and ipsilateral Edinger-Westphal nuclei.
Preganglionic parasympathetic fibres from Edinger-Westphal travel along with CNIII and then exit the inferior branch of CNIII to synapse on the ciliary ganglion. From the ciliary ganglion, postganglionic parasympathetic fibres are carried via the short ciliary nerves to innervate the ciliary body muscle and sphincter pupillae.
what is the accomodation reflex
Accommodation is the adaptation of the eye when focusing on a near object. It works by:
- Increasing lens curvature: The ciliary body muscles contract via parasympathetics from Edinger-Westphal, leading to relaxation of the lens zonules.
- Pupil constriction: Activation of the sphincter pupillae via parasympathetics form Edinger-Westphal.
- Eye convergence: Contraction of medial recti via CNIII.
location and role of trochlear nerve
The trochlear nuclei are located in the midbrain at the level of the inferior colliculus. Each trochlear nucleus innervates the contralateral SO muscle.
CNIV passes through the lateral wall of the cavernous sinus inferior to CNIII and enters the SOF above the common tendinous ring.
characteristics of CNIV
● Only cranial nerve to exit dorsally from the brainstem.
● Smallest cranial nerve in number of axons.
● Longest unprotected intracranial course.
pathway of the abducens nerve
The abducens nucleus is located in the pontine tegmentum ventral to the fourth ventricle. The nucleus is located near the paramedian pontine reticular formation (PPRF) and surrounded by looping fibres of CNVII. CNVI exits the brainstem at the pontomedullary junction and crosses over the petrous apex of the temporal bone through an osteofibrous channel, called Dorello’s canal. It is at the Dorello’s canal where CNVI is susceptible to stretching in cases of increased intracranial pressure. CNVI then travels through the cavernous sinus, lateral to the internal carotid. It then enters the orbit via the SOF, through the tendinous ring, to innervate the LR muscle.
pathway for pupillary dilatation
- First-orderneurons:Startattheposterolateralhypothalamusandsynapseatthe intermediolateral cell column between C8 to T2 (ciliospinal centre of Budge).
- Second-order preganglionic neurons: Leave centre of Budge, travel over the lung apex and synapse at the superior cervical ganglion at the carotid bifurcation. This is where sudomotor fibres exit to course with the external carotid and supply the sweat glands of the face.
- Third-order postganglionic neurons: Travel around the internal carotid artery to finally innervate the dilator pupillae via long ciliary nerves (branches of the nasociliary nerve).
what is the SNS responsible for
pupillary dilatation and contraction of Müller muscle.
voluntary movements of they eye are initiated where
frontal eye field (FEF), Brodmann area 8, in the frontal lobe.
eye reflex movements are coordinated where
coordinated via the occipital cortex and superior colliculus in response to a visual stimulus.
what are the three types of movements in supranuclear motor
- Saccadic eye movements
- Smooth pursuit movements
- Vestibulo-ocular movements
define saccades
Saccades are fast eye movements which involve the rapid fixation of a desired object onto the fovea with abrupt change of point of fixation when switching from one object to the next. Saccades can have an angular speed of 600°/s, lasting around 30–100 milliseconds after a latency (time it takes to initiate) of approximately 200 milliseconds
what is smooth pursuit
This refers to slow movements of the eye designed to keep a moving stimulus fixed at the fovea. They have a latency of about 100 milliseconds, and a much slower velocity than saccades. They are initiated from parieto-occipital areas
what is vestibulo-ocular movements
These eye movements stabilize the eye relative to head movements. When moving the head, with eyes fixed on an object, sensory information of the semicircular canals results in the movement of the eyes in the opposite direction to the head movement. This occurs via projections from the vestibular nuclei to cranial nerves and PPRF.
what is optic neuropathy
refers to damage of the optic nerve
