Eye and Visual Pathways PDF

EYE AND VISUAL PATHWAYS By: Dr. Shahnaz Sabetkam Assistant Professor of Anatomical Sciences Kyrenia University  ORBIT The orbits bony cavities: Bilateral structures In the upper half of the face Below the anterior cranial fossa Anterior to the middle cranial f...

EYE AND VISUAL PATHWAYS By: Dr. Shahnaz Sabetkam Assistant Professor of Anatomical Sciences Kyrenia University  ORBIT The orbits bony cavities: Bilateral structures In the upper half of the face Below the anterior cranial fossa Anterior to the middle cranial fossa The orbits contain: The eyeball, The optic nerve The extraocular muscles The lacrimal apparatus Adipose tissue Fascia The nerves and vessels (Out of 12 pairs of cranial nerves; II, III, IV, VI, a part of V, and some sympathetic fibres)  Features of Orbit The orbits are pyramidal cavities Situated on each side of the root of the nose. They provide sockets for rotatory movements of the eyeball. The long axis of the each orbit passes backwards and medially. The medial walls are parallel to each other at a distance of 2.5 cm but the lateral walls are set at right angles to each other.  Contents of Orbits 1) Eyeball: Eyeball occupies anterior one-third of orbit 2) Fascia: Orbital and bulbar 3) Muscles: Extraocular and intraocular 4) Vessels: Ophthalmic artery, superior and inferior ophthalmic veins, and lymphatics. 5) Nerves: Optic, oculomotor, trochlear and abducent; branches of ophthalmic and maxillary nerves, and sympathetic nerves. 6) Lacrimal gland 7) Orbital fat  Visual Axis and Orbital Axis Axis passing through centers of anterior and posterior poles of the eyeball is known as visual axis. It makes an angle of 20–25° with the orbital axis Orbital axis line passing through optic canal and center of base of orbit.  AXES OF EYEBALL OCULAR (visual) AXIS - anterior pole- posterior pole - parallel in two eyeballs OPTIC (Orbital) AXIS - posterior pole of lens- fovea centralis - Not parallel in two eyeballs EQUATOR OF EYEBALL  The roof (superior wall) of the bony orbit Medially, the trochlear fovea, Attachment of a pulley through which the superior oblique muscle passes 4 3 2 1 Laterally, the lacrimal fossa for the orbital part of the lacrimal gland.  Medial wall of the bony orbit Anterior and posterior ethmoidal foramina lacrimal groove, which contains the lacrimal sac 4 3 2 1 and is bound by the posterior lacrimal crest (part of the lacrimal bone) and the anterior lacrimal crest (part of the maxilla).  The floor (inferior wall) of the bony orbit Inferior orbital fissure Infraorbital groove and canal (foramina) Lateral wall of the bony orbit Superior orbital fissure Zygomaticofacial and zygomaticotemporal foramina  Orbital fracture Fractures of the orbit are not uncommon and may involve the orbital margins with extension into the maxilla, frontal, and zygomatic bones. Fractures within the orbit frequently occur within the floor and the medial wall. Floor fractures are one of the commonest types of injuries. These fractures may drag the inferior oblique muscle and associated tissues into the fracture line. In these instances, patients may have upward gaze failure (upward gaze diplopia) in the affected eye. Medial wall fractures characteristically show air within the orbit in radiographs.  Eyelids Palpebral fissure, the space between the eyelids, when they are open The layers of the eyelids, from anterior to posterior, consist of: skin, subcutaneous tissue voluntary muscle the orbital septum the tarsus, and conjunctiva The upper and lower eyelids are basically similar in structure except for the addition of two muscles in the upper eyelid.  Skin and subcutaneous tissue The skin of the eyelids is not particularly substantial, and only a thin layer of connective tissue separates the skin from the underlying voluntary muscle layer. The thin layer of connective tissue and its loose arrangement account for the accumulation of fluid (blood) when an injury occurs.  Orbicularis oculi 1. The palpebral part (which is in the eyelids) 2. An orbital part The orbicularis oculi is innervated by the facial nerve [VII] Action: closes the eyelids The palpebral part is thin and anchored medially by the medial palpebral ligament, which attaches to the anterior lacrimal crest and laterally blends with fibers from the muscle in the lower eyelid at the lateral palpebral ligament. 3. A third part of the orbicularis oculi muscle (The lacrimal part) that can be identified consists of fibers on the medial border, which pass deeply to attach to the posterior lacrimal crest. The lacrimal part of the orbicularis oculi, which may be involved in the drainage of tears.  Orbital septum Deep to the palpebral part of the orbicularis oculi is an extension of periosteum into both the upper and lower eyelids. This is the orbital septum, which extends downward into the upper eyelid and upward into the lower eyelid. The orbital septum attaches to: The tendon of the levator palpebrae superioris muscle in the upper eyelid The tarsus in the lower eyelid.  Tarsus and levator palpebrae superioris Providing major support for each eyelid is the tarsus. There is a large superior tarsus and a smaller inferior tarsus. These plates of dense connective tissue are attached medially to the anterior lacrimal crest of the maxilla by the medial palpebral ligament and laterally to the orbital tubercle on the zygomatic bone by the lateral palpebral ligament.  Tarsus and levator palpebrae superioris Between the upper and lower eyelids is one unique difference. Associated with the tarsus in the upper eyelid is the levator palpebrae superioris muscle, which raises the eyelid. Origin is from the posterior part of the roof of the orbit Insertion is the anterior surface of the superior tarsus, with the possibility of a few fibers attaching to the skin of the upper eyelid. It is innervated by the oculomotor nerve [III]. In companion with the levator palpebrae superioris muscle is a collection of smooth muscle fibers passing from the inferior surface of the levator to the upper edge of the superior tarsus. Innervated by postganglionic sympathetic fibers from the superior cervical ganglion, this muscle is the superior tarsal muscle. Loss of function of either the levator palpebrae superioris muscle or the superior tarsal muscle results in a ptosis or drooping of the upper eyelid.  Conjunctiva The structure of the eyelid is completed by a thin membrane (the conjunctiva), which covers the posterior surface of each eyelid. This membrane covers the full extent of the posterior surface of each eyelid before reflecting onto the outer surface (sclera) of the eyeball. It attaches to the eyeball at the junction between the sclera and the cornea. With this membrane in place, a conjunctival sac is formed when the eyelids are closed, and the upper and lower extensions of this sac are the superior and inferior conjunctival fornixes.  Tarsal Glands Chalazion These glands are modified sebaceous glands and secrete an oily substance that increases the viscosity of the tears and decreases the rate of evaporation of tears from the surface of the eyeball. Blockage and inflammation of a tarsal gland is a chalazion and is on the inner surface of the eyelid. The tarsal glands are not the only glands associated with the eyelids. Associated with the eyelash follicles are sebaceous and sweat glands. Blockage and inflammation of either of these is a stye and is on the edge of the eyelid. Stye  Vessels of eyelids ✓ The supratrochlear, supraorbital, lacrimal, and dorsal nasal arteries from the ophthalmic artery ✓ The angular artery from the facial artery ✓ The transverse facial artery from the superficial temporal artery; and branches from the superficial temporal artery itself. Venous drainage follows: An external pattern through the various arteries An internal pattern through connections with the ophthalmic veins.  Sensory Innervation of Eyelids The supra-orbital, supratrochlear, infratrochlear, and lacrimal branches of the ophthalmic nerve [V1] The infraorbital branch of the maxillary nerve [V2]  Motor Innervation of Eyelids Motor innervation is from: The facial nerve [VII], which innervates the palpebral part of the orbicularis oculi The oculomotor nerve [III], which innervates the levator palpebrae superioris Sympathetic fibers, which innervate the superior tarsal muscle.  Horner’s syndrome Horner’s syndrome is caused by any lesion that leads to a loss of sympathetic function in the head. It is characterized by three typical features: Pupillary constriction due to paralysis of the dilator pupillae muscle, partial ptosis (drooping of the upper eyelid) due to paralysis of the superior tarsal muscle Absence of sweating on the ipsilateral side of the face and the neck due to absence of innervation of the sweat glands. The commonest cause for Horner’s syndrome is a tumor eroding the cervicothoracic ganglion, which is typically an apical lung tumor. Surgically induced Horner’s syndrome A surgically induced Horner’s syndrome may be necessary for patients who suffer severe hyperhidrosis (sweating). Treatment is relatively straightforward. The patient is anesthetized and a bifurcate endotracheal tube is placed into the left and right main bronchi. A small incision is made in the intercostal space on the appropriate side, and a surgically induced pneumothorax is created. The patient is ventilated through the contralateral lung. Using an endoscope the apex of the thoracic cavity can be viewed from inside and the cervicothoracic ganglion readily identified. Obliterative techniques include thermocoagulation and surgical excision. After the ganglion has been destroyed, the endoscope is removed, the lung is reinflated, and the small hole is sutured.  Lacrimal apparatus is involved in the production, movement, and drainage of fluid from the surface of the eyeball. It is made up of: the lacrimal gland and its ducts the lacrimal canaliculi the lacrimal sac the nasolacrimal duct. The lacrimal gland is anterior in the superolateral region of the orbit and is divided into two parts by the levator palpebrae superioris  Lacrimal apparatus The larger orbital part is in a depression, the lacrimal fossa, in the frontal bone. The smaller palpebral part is inferior to the levator palpebrae superioris in the superolateral part of the eyelid. Numerous ducts empty into superior fornix of the conjunctiva. The fluid accumulates medially in the lacrimal lake and is drained from the lake by the lacrimal canaliculi, one canaliculus associated with each eyelid. T The lacrimal punctum is the opening through which fluid enters each canaliculus. the lacrimal canaliculi join the lacrimal sac between the anterior and posterior lacrimal crests, posterior to the medial palpebral ligament and anterior to the lacrimal part of the orbicularis oculi muscle.  The innervation of the lacrimal gland Involves three different components: 1-Sensory innervation Sensory neurons from the lacrimal gland return to the CNS through the lacrimal branch of the ophthalmic nerve [V1] 2- Secretomotor (parasympathetic) innervation These preganglionic parasympathetic neurons leave the CNS in the facial nerve [VII], enter the greater petrosal nerve (a branch of the facial nerve [VII]), and continue with this nerve until it becomes the nerve of the pterygoid canal.  The innervation of the lacrimal gland ❑ The nerve of the pterygoid canal joins the pterygopalatine ganglion. The postganglionic neurons join the maxillary nerve and continue with it until the zygomatic nerve branches from it, and travel with the zygomatic nerve until it gives off the zygomaticotemporal nerve, which eventually distributes postganglionic parasympathetic fibers in a small branch that joins the lacrimal nerve. 3-Sympathetic innervation Postganglionic sympathetic fibers originating in the superior cervical ganglion travel along the plexus surrounding the internal carotid artery. They leave this plexus as the deep petrosal nerve and join the parasympathetic fibers in the nerve of the pterygoid canal.  Fissures and foramina 1-Optic canal ✓ At the round opening at the apex of the pyramidal- shaped Opens into the middle cranial fossa ✓ Is bounded medially by the body of the sphenoid and laterally by the lesser wing of the sphenoid ✓ Passing through, the optic nerve and the ophthalmic artery Fissures and foramina 2- Superior orbital fissure ✓ Lateral to the optic canal ✓ Between the orbit and the middle cranial fossa ✓ The superior and inferior branches of the oculomotor nerve [III] ✓ The trochlear nerve [IV] ✓ The abducent nerve [VI] ✓ The lacrimal, frontal and nasociliary branches of the ophthalmic nerve ✓ The superior ophthalmic vein  Fissures and foramina 3-Inferior orbital fissure Its borders are the greater wing of the sphenoidand the maxilla, palatine, and zygomatic bones. This long fissure allows communication between: the orbit and the pterygopalatine fossa the orbit and the infratemporal fossa in the middle, the orbit and the temporal fossa Passing the maxillary nerve and its zygomatic branch, the infra- orbital vessels, and a vein communicating with the pterygoid plexus.  Fascial specializations 1-Periorbita The periosteum lining the bones that form the orbit is the periorbita. It is continuous at the margins of the orbit with the periosteum on the outer surface of the skull and sends extensions into the upper and lower eyelids (the orbital septa). At the various openings where the orbit communicates with the cranial cavity, the periorbita is continuous with the periosteal layer of dura mater. In the posterior part of the orbit, the periorbita thickens around the optic canal and the central part of the superior orbital fissure. This is the point of origin of the four rectus muscles and is the common tendinous ring.  2-Fascial sheath of the eyeball The fascial sheath of the eyeball (bulbar sheath) is a layer of fascia that encloses a major part of the eyeball: Posteriorly, it is firmly attached to the sclera Anteriorly, it is firmly attached to the sclera near the edge of the cornea. Additionally, as the muscles approach the eyeball, the investing fascia surrounding each muscle blends with the fascial sheath of the eyeball as the muscles pass through and continue to their point of attachment. A specialized lower part of the fascial sheath of the eyeball is the suspensory ligament , which supports the eyeball. This “sling-like” structure is made up of the fascial sheath of the eyeball and contributions from the two inferior rectus muscles and the medial and lateral rectus muscles. Check ligaments of the medial and lateral rectus muscles Other fascial specializations in the orbit are the check ligaments. These are expansions of the investing fascia covering the medial and lateral rectus muscles, which attach to the medial and lateral walls of the orbit. The medial check ligament is an extension from the fascia covering the medial rectus muscle and attaches immediately posterior to the posterior lacrimal crest of the lacrimal bone. The lateral check ligament is an extension from the fascia covering the lateral rectus muscle and is attached to the orbital tubercle of the zygomatic bone.  Muscles of Eyes There are two groups of muscles within the orbit: Extrinsic muscles of eyeball (extra-ocular muscles) involved in movements of the eyeball or raising upper eyelids, and Intrinsic muscles within the eyeball, which control the shape of the lens and size of the pupil. 1-M.levator palpebrale sup. and the superior tarsal m 2-M.rectus superior 3-M.rectus inferior 4-M.rectus medialis 5-M.rectus lateralis 6.M.obliquus superior 7.M.obliguus inferior  Extrinsic muscles Of the seven muscles in the extrinsic group of muscles, one raises the eyelids, whereas the other six move the eyeball itself. The movements of the eyeball, in three dimensions are: Elevation—moving the pupil superiorly Depression—moving the pupil inferiorly Abduction—moving the pupil laterally Adduction—moving the pupil medially  Loss of oculomotor nerve [III] function results in complete ptosis or drooping of the superior eyelid, whereas loss of sympathetic innervation to the superior tarsal muscle results in partial ptosis. The “H-test” A simple “formula” for remembering the nerves that innervate the extraocular muscles is “LR6SO4 and all the rest are 3” (lateral rectus [VI], superior oblique [IV], all the rest including levator palpebrae superioris are [III]). The function of all extrinsic muscles and their nerves [III, IV, VI] that move the eyeball in both orbits can all easily be tested at the same time by having the patient track, without moving his or her head, an object such as the tip of a pen or a finger moved in an “H” pattern—starting from the midline between the two eyes. Thank you