Eye & optic nerve Enas omar · So right optic tract carries lateral fibers of right retina & medial fibers of left retina An optic nerve lesion can cause ipsilateral, contralateral

Eye & optic nerve Enas omar

Contents of the lecture : 1 – Eyelids 2- optic nerve 3- layers of the eyeball slides are included , but you have to go back to them to see the pictures. __________________________________________________

Eyelids

An eyelid is a thin fold of skin that covers and protects the human eye. The upper & lower eyelids meet at medial & lateral angles ( inner & outer canthi respectively ).

The palpebral fissure is the elliptic space between the medial and lateral canthi of the two open lids. In simple terms, it refers to the opening between the eye lids. The eyelids show a row of eyelashes on the free margin .

*framework : The orbital septum : is a membranous sheet that acts as the anterior boundary of the orbit. It extends from the orbital rims to the eyelids. It forms the fibrous portion of the eyelids.

tarsal plates : are two comparatively thick, elongated plates of dense connective tissue, one is found in each eyelid, and contributes to its form and support. They are fixed laterally & medially by palpebral ligaments.

Glands of the eyelid : 1- gland of Zeis (oil) : attached with hair follicle ( service the eyelashes ). 2- gland of Moll ( modified sweat ) :also called ciliary glands . 3- tarsal – Meibomian gland- ( modified oil) : the largest gland which are located behind eyelashes mainly within tarsal plates . Muscles : 1- orbicularis oculi : circular voluntary .formed of skeletal muscle fibers & receive nerve supply from the facial nerve . Responsible for the facial expression. 2- levator palpebra superiosis : elevate the upper eyelid. Conjunctiva : A thin, clear, moist membrane that coats the inner surfaces of the eyelids (palpebral conjunctiva) and the outer surface of the eye (ocular, or bulbar, conjunctiva). It is highly vascularized . So redness of eye is due to blood vessels that are found in the conjunctiva . The fornix of the conjunctivae refers to loose arching folds connecting the conjunctival membrane lining the inside of the eyelid with the conjunctival membrane covering the eyeball. Part of it is the superior fornix which is located near the lacrimal gland laterally. Conjunctival sac : the space bound by the conjunctival membrane between the palpebral and bulbar conjunctiva, into which the lacrimal fluid is secreted; it is a closed space when eye is closed; when eye is open, the sac is open anteriorly through the palpebral fissure (between the eyelids).

Now let us define some words and under stand the story of lacrimal apparatus :

1- lacus lacrimalis : A small triangular space of the conjunctiva of the eye that is present at the medial angle of the eye in which the tears will accumulate after cleaning the anterior surfaces of the conjunctiva and the eyeball.

2- caruncula lacrimalis : is the small, pink, globular nodule at the inner corner (the medial canthus) of the eye.

3- papilla lacrimalis : a small conical elevation, the apex of which is pierced by a small orifice, the punctum lacrimale( point )

4- lacrimal canaliculi : small channels on each eyelid that commence at the lacrimal puncta .

The lacrimal canaliculi will unit with lacrimal sac & descends into the nose as nasolacrimal duct then opens in the nasal cavity. Here is a summary to guarantee our work : ( wink emoji ) 1- the lacrimal gland secretes fluid 2- movement of the eyelid will push the fluid toward lacrimal canaliculi 3- fluid will move into lacrimal sac 4- lacrimal sac will continue as nasolacrimal duct which will empty in the nasal cavity .

Lacrimal gland : The lacrimal glands are paired, almond-shaped exocrine glands, one for each eye, that secrete the aqueous layer of the tear film. They are situated in the upper lateral region of each orbit, in the lacrimal fossa (in which we find the lacrimal sac which drains into nasolacrimal duct of) the orbit formed by the frontal bone. Consist of two parts : Orbital & palpebral ( the smallest) and the levated palpebral superioris lies in the space between them . Ducts open into sup fornix. Nerve supply : Sympathetic : internal carotid plexus Parasympathetic : facial n greater petrosal nerve ( in middle ear ) cranial cavity infraorbital fossa infratemporal fossa ( join deep petrosal n ) then join nerve of ptergoid canal ( that has ganglion in ptergopalatine fossa ) postganglionic neuron toward orbit by zygomatic n ( branch of maxillary n) from inf orbital fissure toward lacrimal n toward lacrimal gland . # done with eyelids uhhh :p _________________________________________________

Optic nerve Entirely sensory (SSA) – Vision • Rods and cones of the retina

→ bipolar neurons → ganglion cells Optic nerve fibers via optic foramen Optic chiasm*

Optic tracts Superior colliculi ** (midbrain) •Lateral geniculate nuclei (thalamus) Optic radiation

Primary visual areas – (cerebral cortex) •* fibers from the medial half of each retina cross to the opposite side and fibers from the lateral side remain on the same side •

**control the extrinsic and intrinsic eye muscles

So right optic tract carries lateral fibers of right retina & medial fibers of left retina An optic nerve lesion can cause ipsilateral, contralateral or both visual field defects depending on its size and location. The nasal half of the retina projects to the contralateral hemisphere and serves the half of the visual field on the same side as that eye; but the temporal half of the retina projects to the ipsilateral hemisphere and serves the half of the visual field on the side opposite that eye. So before the optic nerves join at the chiasm, each carries information from both visual fields.. Optic nerve lesions : 1- right monocular blindness : lesion in optic nerve. 2-bitemporal heminopia : associated with lesions of the optic chiasm ( the area where nasal – medial- fibers cross over)/ loss of vision in the lateral visual field of both sides. 3- homonymous heminopia : lesion in optic tract / when the lesion occur in right optic tract , left visual field of both sides or of one side is lost .

Layers of eyeball Fibrous Tunic (outer layer) – Cornea ‐ anterior – Sclera ‐ posterior •Vascular Pigmented Tunic (middle layer) – Choroid – Ciliary body – Iris • Nervous Tunic (inner layer)

Cornea : • Transparent layer covering the iris,pupil & ant chamber. • Helps focus light (refraction) – Astigmatism • 3 layers – nonkeratinized stratified squamous – collagen fibers & fibroblasts – simple squamous epithelium • Transplants – common & successful – no blood vessels so no antibodies to cause rejection • Nourished by tears (externally)& aqueous humor(internally) & air ( directly) • Nerve supply: long ciliary nn. (V1) ( innervated with sensory nerve fibers via the opthalmic division of the trigeminal n by way of 70-80 long ciliary nerves ).

Sclera : outer layer of the eyeball . It is continuous with

the cornea at the front of the eye. • “White” of the eye • Dense irregular connective tissue layer ‐‐ collagen & fibroblasts • Provides shape & support for all other layers & it is the insertion site for extraocular muscles. •At the junction (limbus) of the sclera and cornea is an opening (scleral venous sinus) • Posteriorly pierced by the Optic Nerve (CNII) – Lamina cribrosa

Vascular Tunic ‐‐ Choroid & Ciliary Body • Choroid pigmented epithelial cells (melanocytes) (outside) & blood vessels (inside) – provides nutrients to retina – black pigment in melanocytes absorb scattered light • Ciliary body ( choroid ends with ciliary body) – Ciliary ring (posterior) – Ciliary processes ( finger like projections attached to lense by suspensory ligaments). • folds on ciliary body – Suspensory ligaments • secrete aqueous humor – Ciliary muscle controls tension on ligaments & lens. • smooth muscle that alters shape of lens

Vascular Tunic ‐‐ Iris & Pupil ( pupil is a foramen

within the iris) • Colored portion of eye • Shape of flat donut suspended between cornea & lens – Anterior & posterior chambers • Hole in center is pupil • Function is to regulate amount of light entering eye • Autonomic reflexes – circular muscle fibers contract in bright light to shrink pupil ( parasympathetic) – radial muscle fibers contract in dim light to enlarge pupil ( sympathetic) muscles of the iris : • Constrictor pupillae (circular) ‐‐‐‐‐parasympathetic fibers • Dilator pupillae (radial) ‐‐‐‐‐sympathetic fibers. Response varies with different levels of light

Lens • Avascular • Layers – Capsule‐ Clear & perfectly transparent – Epithelium ‐ anterior( cuboidal epithelium which is found anteriorly ONLY. – Crystalline proteins‐ concentric layers • Lens held in place by suspensory ligaments • Focuses light on fovea

Cataract • البيضا المي – Cloudiness – Lens implants ( easy to be replaced)

Nervous Tunic ‐‐ Retina The retina is the third and inner coat of the eye which is a

light-sensitive layer of tissue • Layers – Outer pigmented layer – Inner nervous layer • Parts – Posterior ¾ is receptor organ • Ora serrata entrance for retinal vessels – Anterior part (nonreceptive) • Covers ciliary processes & back of iris • Macula lutea – Fovea centralis aggregation of receptors , the most acute area that receive visual stimuli in retina. • Optic disc – Optic nerve – Central artery of the retina – Blind spot • Optic disc – optic nerve exiting back of eyeball • Central retinal BV – fan out to supply nourishment to retina – visible for inspection • hypertension & diabetes • Detached retina – trauma (boxing) • fluid between layers • distortion or blindness

The optic disc or optic nerve head is the point of exit for ganglion cell axons leaving the eye. Because there are no rods or cones overlying the optic disc, it corresponds to a small blind spot in each eye. The ganglion cell axons form the optic nerve after they leave the eye. The optic disc represents the beginning of the optic nerve and is the point where the axons of retinal ganglion cells come together. The optic disc is also the entry point for the major blood vessels that supply the retina.

Cavities of the Interior of Eyeball

• Anterior cavity (anterior to lens) – filled with aqueous humor • produced by ciliary body • continually drained • replaced every 90 minutes – 2 chambers • anterior chamber between cornea and iris • posterior chamber between iris and lens ant & post chambers of ant cavity are connected to each other by the pupil. • Posterior cavity (posterior to lens) – filled with vitreous body (jellylike).vitreous body support the retina . – formed once during embryonic life – floaters are debris in vitreous of older individuals

layers of the retina the dr mentioned them briefly & here is the summary of what he said : The retina layers can be simplified into 4 main processing stages: photoreception, transmission to bipolar cells, transmission to ganglion cells which also contain photoreceptors, the photosensitive ganglion cells, and transmission along the optic nerve. At each synaptic stage there are also laterally connecting horizontal and amacrine cells.

from Wikipedia : Inner limiting membrane – basement membrane elaborated by Müller cells Nerve fibre layer – axons of the ganglion cell nuclei (note that a thin layer of Müller cell footplates exists between this layer and the inner limiting membrane) Ganglion cell layer – contains nuclei of ganglion cells, the axons of which become the optic nerve fibres for messages and some

]2[amacrine cells displaced Inner plexiform layer – contains the synapse between the bipolar

]2[and amacrine cells. ganglion axons and the dendrites of the cell Inner nuclear layer – contains the nuclei and surrounding cell bodies (perikarya) of the amacrine cells, bipolar cells and horizontal

]2[cells. Outer plexiform layer – projections of rods and cones ending in the rod spherule and cone pedicle, respectively. These make synapses

region, this is macular In the ]2[with dendrites of bipolar cells.known as the Fiber layer of Henle. Outer nuclear layer – cell bodies of rods and cones External limiting membrane – layer that separates the inner segment portions of the photoreceptors from their cell nucleus Layer of rods and cones – layer of rod cells and cone cells Retinal pigment epithelium – single layer of cuboidal cells (with extrusions not shown in diagram). This is closest to the choroid

Aqueous Humor • Continuously produced by ciliary body • Flows from posterior chamber into anterior through the pupil • Scleral venous sinus – canal of Schlemm – opening in white of eye at junction of cornea & sclera – drainage of aqueous humor from eye to bloodstream

Glaucoma • الزرقا المي – increased intraocular pressure that could produce blindness – problem with drainage of aqueous humor

best wishes