Flashcards in Eye G Lab And Dissection Deck (61):
3 concentric coats of the eyeball
External fibrous coat: sclera posteriorly and cornea anteriorly
Middle and vascular coat: choroid, ciliary body, iris
Internal or retinal coat: outer layer of pigmented cells and inner layers of neural elements posterior to the ora serrata
Four refractive media
Cornea, aqueous humor, lens, vitreous body
Covers the anterior surface of the eyeball (the corneal epithelium) and is attached near the edge of limbus of the cornea (corneoscleral junction). The conjunctiva lines the inner surface of the eyelids (palpebral conjunctiva) and reflects onto the eyeball (bulbar conjunctiva)
Cornea five layers
The cornea is the transparent disk (lack of blood vessels) like anterior portion of the eyeball. It is made up of 5 layers:
Corneal epithelium- lines the outer surface, stratified squamous non-keratinized epithelium, 5 cells thick
Corneal stroma- main layer, 70 broad sheets of collagen
Corneal endothelium- single layer, lines inner surface, adapted for ion-pumping, pumps fluid from the corneal stroma, preventing corneal opacification from excessive hydration.
Held in place by suspensory ligaments composed of zonular fibers. Has an outer capsule of hyaline material (lens epithelium- cuboidal cells). Center region composed of tightly packed cells, which have lost their nuclei and are full of transparent proteins called crystallins. New cells from the lens epithelium are added to the margin of the lens throughout life, but the cells in the center do not undergo replacement.
Avascular and nourished by diffusion
Extends from the base of the iris to the ora serrata
What is at the ora serrata?
Ciliary body- contains the ciliary muscle (smooth muscle), which contraction of decreases tension on suspensory ligaments of lens so it can round up
At the ora serrata, it becomes continuous with the choroid, which is the pigmented, vascular middle layer.
Sheet-like diaphragm anterior to the lens
What does this structure separate?
What muscles does it contain?
Separates the anterior and posterior chambers
Contains the constrictor pupillae and radial fibers of the dilator pupillae which have actions on the pupil
Flow of aqueous humor
Anterior and posterior chambers communicate via the aperture of the pupil. Aqueous humor resembles CSF in composition and is secreted by epithelial cells and ciliary processes in posterior chamber. It flows from there to the anterior chamber through the pupil and provides nutrients to neighboring structures. After filtering through a network of spaces lined by endothelium, the trabecular mesh work, which runs around the circumference of the root of the iris at the periphery of the anterior chamber, the aqueous humor enters the canal of Schlemm, which runs around the whole circumference of the limbus within sclera and drains into veins.
Abnormal drainage of the aqueous humor and a rise in intraocular pressure. Blindness can occur from damage to the nerve cells.
Continuous secretion and resorption of the aqueous humor is responsible for the normal intraocular pressure of 10-22mmHg.
What is the vitreous body made up of?
Scattered spindle shared cells, fine highly dispersed collagen fibers, and an ECM rich in hyaluronic acid.
Where do the retinal ganglion cells collect?
Optic disc where they penetrate the sclera (lamina cribosa) to form the optic nerve. This is also called the blind spot.
Layers of the retina
Innermost layer of the eye and is composed of a non-neural layer pigment epithelial cells which absorb light and prevent distracting back scatter of light into the retina and a neural layer of photoreceptors cells, retinal support cells and nerve cells.
Pigmented, vascular middle layer of posterior 2/3 of eyeball
Choroid- extends from the ora serrata, the anterior margin of the neural retina, to the optic nerve and contains blood vessels and lymphatics supporting the retina. Appears as a dark brown sheet which blends with the sclera in its outer portion, while the inner portion is attached to the pigmented epithelium of retina.
Consequently, separation of the retina occurs between the rods/cones and pigment epithelium.
Blood supply to the retina
Ophthalmic artery- central artery of retina and ciliary arteries. Central artery of the retina branches out from the region of the optic disc to serve inner portions of the retina. Four branches go to the four quadrants of the retina. These branches are end arteries, so if occluded, will result in death of the ganglion cells and total blindness from that quadrant of the eye. The posterior long ciliary arteries penetrate the sclera around the optic disc and form the choroidocapillary plexus in the choroid to provide nutrients to the outer portions of the neural retina (rods and cones)
Posterior short ciliary arteries supply the back of the retina
Ciliary body is made up of
Ciliary muscle- regulated the shape of the lens
Ciliary processes- connected to suspensory ligaments, which adhere to lens via zonule fibers. Ciliary epithelium also secretes aqueous humour.
Passes dorsal to the medial geniculate body and contains optic tract fibers en route to:
Brachium of superior colliculus- fibers en route to pretectal area and superior colliculus for visual reflexes
What is at the level of the optic chiasm?
The anterior limb/genu of the internal capsule
Posterior to the crus cerebri
Posterior to the lentiform nucleus and lateral to the lateral ventricle
Bones of the orbit: base and apex
The base is the orbital margin and the apex is the optic canal
Frontal bone, ethmoid bone, lacrimal bone, maxilla (frontal and orbital surfaces), zygomatic bone, sphenoid bone.
The infraorbital groove and foramen are in what bone of the orbit
The optic canal and the superior orbital fissure are of what bone
The lacrimal fossa is of what bone
Gap between the maxilla and the greater wing of the sphenoid bone.
Medial wall of the orbit formed by the ethmoid bone- since it is paper thin
Roof of the orbit=
Floor of the orbit=
Medial wall of the orbit=
Anterior cranial fossa
Ethmoidal air cells
Medial and lateral palpebral commissures
Medial and lateral angles/canthi
Where the upper and lower eyelids join
The medial and lateral corners of the eye
Pink fleshy bump
Area surrounding the lacrimal caruncle
Small bump on medial end of each eyelid
A small opening at the apex of each lacrimal papilla
The region where the bulbar and palpebral conjunctiva become continuous
The potential space between the bulbar conjunctiva and palpebral conjunctiva
Superior and inferior conjunctival fornices
Give shape to the eyelids
Tarsal glands are embedded in the posterior surface of each tarsal plate. These glands drain by small orifices that are located posterior the eyelashes and secrete an oily substance onto the margin of the eyelid that prevents the overflow of lacrimal fluid.
The lacrimal gland occupies
The lacrimal groove
The lacrimal fossa in the frontal bone under the orbital septum in the superolateral quadrant of the orbit. This gland drains into the superior conjunctival fornix by 6-10 short ducts.
Medial side of the orbital margin
What drains lacrimal fluid from the medial angle of the eye into the lacrimal sac
What extends from the lacrimal sac
Superior and inferior lacrimal canaliculi
The nasolacrimal duct extends inferiorly from the lacrimal sac and enters the inferior meatus of the nasal cavity
Obstruction of the duct of tarsal gland:
Inflammation of a ciliary gland
Chalazion (cyst)- between the tarsal plate and conjunctiva
Hordeolum (stye)- this gland is a sebaceous gland associated with the follicle of an eyelash
Membrane just inferior to the roof of the orbit
Periorbita, lines the bones of the orbit
3 nerves enter the apex of the orbit by passing superior to the extraocular muscles
Name their divisions
Frontal nerve- a branch of cranial nerve V1- courses from the apex of the orbit toward the supraorbital margin. Divides into the supratrochlear and supraorbital nerve
Lacrimal nerve- branch of cranial nerve V1- passes through the superior orbital fissure lateral to the frontal nerve and courses along the lateral wall of the orbit toward the lacrimal gland.
Trochlear nerve- passes through superior orbital fissure medial to frontal nerve to the superior border of the superior oblique muscle.
Levator palpebrae superioris
Attaches to the upper lid and elevates it
Superior oblique muscle
Medial side of the orbit, the tendon of this muscle passes through the trochlea (pulley), bends at an acute angle, and attaches to the posterolateral portion of the eyeball.
Lateral rectus muscle attachment
Lateral side of the orbit. Arises by two heads from the common tendinous ring, which surrounds the optic canal and part of the superior orbital fissure, and it is the posterior attachment of the four rectus muscles.
What nerves passes through the common tendinous ring
Optic nerve, nasociliary nerve (branch of V1), oculomotor nerve, and abducens nerve.
Nasociliary nerve tract
Crosses superior to the optic nerve and gives off several long ciliary nerves to the posterior part of the eyeball.
Branches of the oculomotor nerve and what they innervate
Superior branch- levator palpebrae superioris and superior rectus muscle
Inferior branch- medial rectus, inferior rectus, and inferior oblique muscles
Branch of the internal carotid artery in the eye
Ophthalmic artery- crosses superior to the optic nerve and reaches the medial wall of the orbit. Gives rise to the central posterior ciliary arteries and supraorbital artery
Superior ophthalmic vein
Medial angle of the eye, it anastomoses with the angular vein (tributary of facial vein). It pursues the same course as the ophthalmic artery. Passes between the two heads of the lateral rectus muscle and through the medial part of the superior orbital fissure and ends in the cavernous sinus. *infection of the upper lip, cheeks and forehead may spread through facial and angular veins into the cavernous sinus. Thrombosis of the sinus may result, leading to involvement of abducens nerve and dysfunction of lateral rectus muscle.
Blowout fractures and different affected sinuses
Fractures usually occur at the 3 sutures between the bones forming the orbital margin. The thinness of the medial and inferior walls allow for fracture while the margin stays intact.
An indirect traumatic injury that displaces the walls is a blowout fracture. Fracture of the medial wall may affect involve the ethmoidal and sphenoidal sinuses, whereas fractures of the inferior wall (orbital floor) may involve the maxillary sinus.
Orbital fractures often cause
Intra-orbital bleeding, which exerts pressure on the eyeball, causing exopthalmos, which is protrusion of the eyeball
Closeness of the optic nerve to the sphenoidal and posterior ethmoidal sinuses, a tumor may erode the thin bony walls and compress the nerve and produce exopthalmos.
The easiest entrance to the orbital cavity for a tumor in the middle cranial fossa is through the superior orbital fissure; tumors in the temporal or infratemporal fossa gain access to this cavity through the inferior orbital fissure.
Lateral side of eyeball is a good approach for operations, because a lot of the eyeball is exposed when the eye is turned medially as far as possible, because the lateral wall does not reach as far anteriorly as the medial wall does
Injury to nerve supplying eyelids
Oculomotor nerve- paralysis of the levator palpebrae superioris= ptosis
Facial nerve- paralysis of orbicularis oculi, preventing the eyelids from closing fully and normal rapid protective blinking is lost
Loss of tonus of inferior eyelid muscles causes lid to evert/fall away from eyeball, leading to drying of cornea and eyeball unprotected, which leads to excessive and inefficient lacrimal fluid
Inflammation of palpebral glands
Ducts of the ciliary glands are obstructed- painful red pus producing swelling or sty (hordeolum) develops on the eyelid. Cysts of the sebaceous glands of the eyelid, called chalazia, may also form. An obstruction of the tarsal gland produces inflammation, a tarsal chalazion, that protrudes toward the eyeball and rubs against it as the eyelids blink.
Bright or dark red patches deep to and within the bulbar conjunctiva
From injury or inflammation
From paroxysms of coughing or violent sneezing can cause rupture of small BVs
Development of the retina and optic nerve
From the optic cup, an outgrowth of the embryonic forebrain, the optic vesicle. As it envaginates from the forebrain, the optic vesicle carries developing meninges with it, why the optic nerve is invested with cranial meninges and an extension of SAS. The central artery and vein of the retina cross the SAS and run to the optic nerve. The pigment layer of the retina develops from the inner layer of the cup.
Layers of the developing retina are separated in the embryo by an intraretinal space, until the layers fuse. Although the pigment layer become firmly fixed to the choroid, its attachment to the neural layer is not firm. So, detachment may follow a blow to the eye. Results in seepage of fluid between the neural and pigment cell layers of the retina. Flashes of light or specks of floating in front of the eye
Pupillary light reflex
CN II- afferent
CN III- efferent
When light enters one eye, both pupils constrict because each retina sends fibers into the optic tracts of both sides. The sphincter pupillae muscle is innervated by parasympathetic fibers, so interruption will cause dilation/slowness of reflex, which is the first sign of compression of the oculomotor nerve on the ipsilateral side
Inflammation of the vascular layer of the eyeball (uvea), may progress to severe visual impairment and blindness if the inflammation is not treated
An increase in CSF pressure slows venous return from the retina, causing edema of the retina that is viewed during opthalmoscopy as swelling of the optic disc. Normally the disc is flat and does not form a papilla.
Increased CSF and intracranial pressure in the extension of the SAS around the optic nerve
Presbyopia and cataracts
As people age, their lenses become harder and more flattened. Reduce focusing power of the lenses- presbyopia.
Loss of transparency (cloudiness) of the lens- cataracts
Colomba of iris
Absence of a section of iris- birth defect, where the choroid fissure fails to close properly, from penetrating or nonpenetrating injuries to the eye, or surgery.
The iridial fissure does not heal
Hemorrhage within the anterior chamber- from blunt trauma
Initially the chamber is tinged red, but blood soon accumulates.
Touch cornea with a wisp of cotton= blink
Absence of a blink suggests a lesion of CN V1 (cornea sensory innerv.) or CN VII (motor nerve to orbicularis oris)
Interruption of the cervical sympathetic trunk and is manifest by the absence of sympathetically stimulated function on the ipsilateral side of the head: miosis, drooping of superior eyelids/ptosis, redness and increased temperature of skin (vasodilation), and anhydrosis
Paralysis of extra-ocular muscles/palsies of orbital nerves
By disease in brain stem or by head injury resulting in diplopia when one attempts to use a muscle
Oculomotor nerve palsy
Affects most of the ocular muscles, levator palpebrae superioris, and the sphincter pupillae.
Droop of superior eyelid because of unopposed action of orbicularis oculi (facial nerve)
Pupil is fully dilated and unreactive because of unopposed dilator pupillae.
Pupil is fully abducted and depressed (down and out) because of the unopposed action of the lateral rectus and superior oblique, resp.
Cannot abduct the pupil on affected side
Pupil is fully adducted by unopposed medial rectus muscle