Ocular Anatomy Orbit & eye mbbs, india

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Orbit and Eye

DR . WAI WAI KYIMBBS, B 18, 2013

Objectives

• Bony orbit • Contents of orbit• Structure and different components of the eye ball • Extra ocular muscles• Nerves and vessels of orbit.• The Ocular Adnexa Eyelid, conjunctiva and lacrimal apparatus• Clinical relevance

Bony orbit: shape/ orientation

The orbits are bony cavities. It is a four-sided pyramidal or cone-shaped cavities with the base at the anterior orbital margin and the apex at theposterior margin within the skull. The medial wall of the orbit is parallel to the median sagittalplane. The lateral wall is at a 45° angle from the median sagittal plane; perpendicular to one another.

The orbits divergebut the optic axes are parallel.

Bony orbit (The seven bones make up the bony orbit)

1. Frontal, 2. Sphenoid (greater and lesser wings), 3. Zygomatic4. Maxilla, 5. Lacrimal, 6. Palatine, and 7. Ethmoid

Palatine

Lateral Medial

Bony orbit has ■ The roof /superior wall- orbital plate of frontal

■ The floor /inferior wall - maxilla and zygomaticVery thin, can be damaged in blow-out fracture causing eye tosink into maxillary sinus.The infra orbital groove/canal weaken the already thin floor further.

■ Lateral wall - frontal, zygomatic and sphenoid

■ Medial wall

Lateral Medial

Frontal bone

Lesser wing of sphenoid

Zygomatic

Palatine

Maxilla

Infra orbital groove

■ Medial wall - frontal, maxilla, lacrimal, orbital plate of ethmoid, sphenoid

♦The roof is separated from the lateral wall by the superior orbital fissure

♦The inferior orbital fissure separates the floor from the lateral wall

Medial wall

Lateral Medial

Lacrimal fossa

Optic foramen/ canal

Infraorbital formen

Superior orbital fissure

Inferior orbital fissure

Blowout fracture

Tripod fracture

Left Frontal View of Skull

1. Frontal bone 2. Nasal bone 3. Lacrimal bone 4. Maxillary bone 5. Zygomatic bone 6.Temporal bone

7. Parietal bone 8. Greater wing of

sphenoid bone 9. Zygomatic process of

temporal bone 10.Lesser wing of

sphenoid bone 11.Ethmoid bone 12.Palatine bone

Margins of the orbit Is formed by the: • Frontal• Zygomatic & • Maxillary bones

Suprorbital notch

Infraorbital formen

Frontal

MaxillaryZygomatic

Openings into the orbital cavity ( Fissures, canals and foramina) Optic foramen or canal ▪ In the lesser wing of sphenoid, superomedial to the superior orbital fissure. ▪ Connects the orbit with the middle cranial fossa ▪ It transmits the optic nerve (II), ophthalmic artery, a branch from the internal carotid.

Supraorbital notch or foramen

▪ Transmits supraorbital vessels, supraorbital nerve (V) Infraorbital groove/canal & Infraorbital foramen

▪ Within the maxillary bone

▪ Infraorbital nerve (continuation of maxillary nerve) and vessels Nasolacrimal Canal

▪ Communicates with inferior meatus of the nose

Superior orbital fissure

▪ Lies between lesser and greater wings of sphenoid bone

▪ Transmits ○ CN III (oculomotor) (sup.& inferior divisions) ○ IV (trochlear) ○ V1 (ophthalmic n) ▪ Lacrimal ▪ Frontal ▪ Nasociliary nerves ○ VI (abducens) ○ Ophthalmic veins ○ Optic nerve & ophthalmic artery & central artery of retina ▪ Communicates with the middle

cranial fossa

Inferior orbital fissure▪Transmits - maxillary division of CN(V) and its zygomatic branch, inferior ophthalmic vein▪ Communicates with the infratemporal & pterygopalatine fossae

Frontal nTrochlear nerve

Nasociliary n

Abducens n

Oculomotor nerve: Sup & inf division

Optic foramen or canal

Structures pass through the

Superior orbital fissure (SOF)

A. Structures pass through the SOF outside the tendinous ring

B. Structures pass through the SOF inside the tendinous

The eye ball

The eye (eye ball) is the organ of vision & the principal component of the visual apparatus.

The orbit is the bony cavity

Contents of the orbit

1.Eyeball and optic nerve

2. Extra-ocular muscle

3. The Ocular adnexa; eyelid, lacrimal gland and lacrimal sac

4. Vessels - Ophthalmic artery, superior & inferior ophthalmic veins & lymphatics

5. Nerves- Optic, oculomotor, trochlear, ophthalmic nerve, abducent & ciliary ganglion & sympathetic nerves

5. Fats and fasciae (Orbital pad of fat & orbital & bulbar fasciae)

Tunics of the Eye

1. Outer Fibrous layer Sclera Cornea 2. Middle vascular layer/ Uvea or uveal tract i. Iris ii. Choroid iii. Ciliary body

(includes zonular fibers, ciliary muscles, and ciliary processes) The ciliary body is closely associated with the: ▪ Lens ▪ Trabecular meshwork ▪ Canal of Schlemm

3. Inner nervous layer Retina

Cornea

Retina

Lens capsule

Anterior chamber

Posterior chamber

Macula

Suspensory ligaments

Conjunctiva

Ora serrata

Central artery& vein of retinaCiliary body

Optic nerve

Schlemm’s canal

Lateral rectus

Medial rectus Sclera Choroid

Outer Tunic:

a. Sclera: White fibrous part of outer tunic posterior five-sixths of the tunic(eyeball), provides shape & protects inner parts.

b. Cornea: Transparent anterior one-sixth of outer layer of eye, refracts (bends) light, no blood vessels

Middle Tunic:

It consists of the: a.Choroid: Vascular part of middle tunic, provide blood supply; form a pigmented layer.

b. Ciliary body: contains the ciliary muscle which alters shape of lens for near and far vision; ciliary processes secretes aqueous humor c. Iris: thin diaphragm that regulates

pupil size & controls light.

The cornea is composed of 5 layers, from the front to the back, (the ABC’s) : 1. Anterior epithelium (most

anterior layer)2. Bowman’s (anterior limiting)

membrane 3. Central stroma (substantia

propria, largest layer) 4. Descemet’s (posterior limiting)

membrane 5. Endothelium (posterior

epithelium, contains pump)

The corneal epithelium is very rich in free nerve endings (trigeminal sensory) that make the cornea extremely sensitive to pain.

The cornea

Corneal blood supply- The cornea contains no blood vessels and gets Its nourishment from the: ▪ Tears ▪ Aqueous humor that fills the chamber behind it - Conjunctival & episcleral capillary net works located in the limbus

Nerve supply of cornea Ophthalmic division of the Trigeminal nerve, mainly through the long ciliary nerves

Corneal wound healing- Corneal epithelium – regenerates quickly- Bowman’s layer – not regenerate, replaced by epithelial cell or stromal scar tissue -Stroma – replaced tissue slightly different from those of original tissue so scar may result - Descemet’s membrane – very strong & resistant, regenerated by endothelial cells - Endothelial cells – not replaced but migrate to cover the area

Function of the cornea

The cornea has 2 primary functions; refraction & transmission of the light

1. Light refraction (bending of the light ray): It must remain transparent to refract light properly.

2. Transmission of the light Minimal scattering & distortion of the transmission of the light is

due to : - smooth optical surface formed by the corneal epithelium & its tear film covering - No blood vessels in the cornea 3. Like the rest of the sclera, structural integrity of the eye.

4.The cornea filters out some of the most damaging ultraviolet (UV) wavelengths in sunlight. Without this protection, the

crystalline lens and the retina would be highly susceptible to injury from UV radiation.

Applied anatomy of cornea

• Cloudy cornea is a loss of transparency of the cornea. Clouding results in varying degrees of visual loss.

• Lack of tear fluid (dry eye) can damage the cornea • Keratitis- inflammation of the cornea. • Astigmatism is a condition in which the uneven curvature of

the cornea blurs and distorts both distant and near objects.

• Corneal Transplant /corneal graft - is performed with corneal tissue from a human donor.

• Corneal erosion or a corneal abrasion - an erosion through a few layers of the epithelium

• Corneal ulcer - an erosion through the entire epithelium and into the stroma. If Descemet's membrane ruptures, the liquid inside the eyeball leaks out and the eye collapses. A corneal ulcer is very painful.

Middle Tunic

The Iris

• Visible colored part of the eye

• Attached to the ciliary body

• Composed of smooth muscle• Pupil – the round, central

opening– Sphincter pupillae muscle

(constrictor or circular)– Dilator pupillae muscle

(dilator or radial)

• Act to vary the size

of the pupil

Pupil:

Central opening in iris that allows light in.

Pupil movements:Mydriasis (dilation) occurs in dark conditions, excitement / fear

Miosis (contraction) occurs in illuminated conditions, during convergence and while sleeping.

Dilator pupillae Muscle: Sympathetic

Sphincter pupillae muscle: Parasympathetic

PupilIris

Pupillary dilator pathway = sympathetic pathway

Applied anatomy

1. Horner’s syndromeLoss of sympathetic innervation to the head. Its effects on the eyes are as follows:▪ Ptosis - upper eyelid droops (denervation of smooth muscle in the eyelid)▪ Anhydrosis - no sweat above the neck▪ Miosis - constriction of pupil from unchecked parasympathetics

2. Argyll Robertson pupil: Miotic, irregular pupil that does not react to light but responds to accommodation, which indicates a lesion in the rostral midbrain; occurs in neurosyphilis and diabetes.

It is the transparent biconvex flexible structure, to focus images on the retina.

Location - situated between iris and the vitreous, suspended from the ciliary processes by Zonules

• No vessels, no nerves• Have a very structured

organization.

-The Lens or Crystalline Lens of Eye

-Structure of the crystalline lensThe crystalline lens is composed of 4 layers, from the surface to the center:

1. Capsule 2. Subcapsular epithelium 3. Cortex 4. Nucleus

1. Lens capsule - The lens capsule is an acellular, transparent, elastic membrane that envelopes the entire lens- Slender but very strong; suspensory ligaments attach to the

lens capsule.

Zonular fibers or Suspensory ligaments of the lens-These are termed zonules of Zinn and arise from the ciliary body to insert into and around the equatorial capsule. Regulate the shape of the lens to change focus from near to far objects.

2. Lens epithelium- A single layer of cuboidal cells present beneath the anterior capsule only. There is no corresponding lens epithelium

posteriorly The crystalline lens is the only structure continuously growing

throughout the life.- Germinative zone give rise to fiber cells; specialized cells

located in front of and adjacent to the lens equator. It is the only lens tissue capable of regeneration throughout life, epithelial cells divide, elongate, denucleate and become new lens fibers which make up the cortex.-

Ciliary m. relaxed

Near-sight accommodation

Far-sight accommodation

Function of the lens- Bend light waves for fine focusing of retinal images- Accommodation

Zonule /suspensory ligaments are strong fibres attaching lens to ciliary body.

Applied anatomy of crystalline lens

Cataract- Cataract is an opacity or cloudiness or of the lens (including

the capsule) which results in loss of transparency of the lens. - As one gets older the lens can also become cloudy. Cataracts

may be caused by congenital defects, persistent exposure to ultraviolet light, or other poorly understood mechanisms. Most cataracts however occur as part of the aging process.

- When cataracts become too severe the lens has to be

removed and be replaced with an artificial lens.The artificial lens is not capable of accommodation.

Operative techniques (Better technique) - (Phacoemulsification & Foldable intraocular lens /IOL)

Lens support - Zonular or suspensory ligaments -The lens is supported posteriorly by the vitreous (hyaloid) face. This is important clinically that the posterior capsule of the lens and vitreous face are tightly adherent.

Lens nourishmentDuring the fetal stage, the development of the lens is aided by the hyaloid artery. In adults, the lens depends entirely upon the aqueous and vitreous humors for nourishment.

The proximal parts of the hyaloid vessels form the central artery and veinof the retina. The distal parts of the hyaloid vesselsdisappear before birth.

Inner Tunic: The retina

Inner Tunic:

a. Retina (containing rods & cones)b. Optic disc (blind spot)c. Macula Fovea centralis

a. The retina It is composed of two basic layers:■ Retinal pigment epithelium■ Neural retina- inner layer which has 9 layers

The neural retina and RPE arise from distinct embryologic layers and the potential space in between is the site of retinal detachment.

The retina is composed of 10 layers, from the outside (nearest the blood vessel enriched choroid) to the inside (nearest the gelatinous vitreous humor):1. Pigmented epithelium2. Photoreceptors; (outer and inner segments of cone and rod) 3. External (outer) limiting membrane4. Outer nuclear (cell bodies of cones and rods)5. Outer plexiform (cone and rod axons, horizontal cell dendrites, bipolar dendrites)6. Inner nuclear (nuclei of horizontal cells, bipolar cells, amacrine cells, and Müller cells)7. Inner plexiform (axons of bipolar cells and amacrine cells, dendrites of ganglion cells8. Ganglion cells (nuclei of ganglion cells) 9. Axons (nerve fibers from ganglion cells traversing the retina to leave the eye at the optic disk)10.Internal limiting membrane (separates the retina from the vitreous)

RetinaContaining three main types ofneurons

▪ Rods & cones (photoreceptors)▪ Bipolar cell▪ Ganglion cell

Converts light stimuli to nerve impulses. Output to brain is via the optic nerve.

Retinal Anatomy

b. Optic disc (blind spot/ optic papilla :

This is where the optic nerve and blood vessels enter the eye. It lies about 4 mm nasal to the macula.

Area where optic nerve originates; no rods or cones

c. Macula: The small sensitive area of the retina that gives central vision; contains the fovea.

Fovea centralis: densely packed cones; provides greatest visual acuity & color vision.

Central retinal a & v Optic disc Macula Fovea

Retina seen through an ophthalamoscope

Rods & cones

Cones▪ Photopic vision, daylight▪ The cones function best under daylight ▪ Essential for visual acuity and color vision ▪ Densest in fovea, which lies in the centre of the macula lutea ▪ High resolution

Rods ▪ Scotopic vision, moonlight ▪ The rods function best in dim light (night vision), are very light sensitive ▪ Vision with the rods is relatively poor but they detect movement ▪ More numerous in proportion at periphery of retina ▪ Less resolution

Old discs at the tip are phagocytized by pigment epithelial cells

Blood supply to the retina• The outer retinal layers receive blood supply from

choriocapillaris (via diffusion)• Inner retinal layers are supplied by the central retinal

the eye with the optic nerve.

Applied anatomy• The retinal artery is an end artery; occlusion results in

blindness

Visual Pathway

1. Rods and cones

2. Bipolar neurons

3. Ganglion cell’s axon forms the optic nerve

4. Optic nerve to the optic

5. Chiasm

6. Optic tract

7. Lateral geniculate nuclei of the thalamus

8. Optic radiations

9. Primary visual areas of the occipital lobes

Retina

Visual Pathways & Fields

• Objects reflect light • Rays refracted by cornea, aqueous humor, lens,

vitreous body and onto retina. • Light stimulus is changed to nerve impulses,

travel thro’ optic nerve to visual cortex in occipital lobe

• Image on retina is upside down & reversed. At the optic chiasm retinal fibers cross over. Right side of brain looks at left side of world.

Visual pathway

Optic nerve leaves the back of the orbit (eye) via the optic canal, running postero-medially towards the optic chiasm, located just below and in front of the pituitary gland. (That is why a tumor on the pituitary gland, pressing on the optic chiasm, can cause vision problems).

Optic chiasmaThe right and left optic nerves converge and partially cross to form the optic chiasma. The nasal half of each retina (temporal visual fields) cross over to the other side; but the nerve fibers originating in the temporal retina do not cross over.

Optic tract The portion of the visual pathway between the optic chiasm and the brain visual system projects to the occipital lobeLateral Geniculate Nucleus (LGN): A nucleus in the thalamus- Most of the axons of the optic nerve terminate in the lateral geniculate

nucleus from where information is relayed to the visual cortex.Optic radiation - a collection of axons from the LGN to the visual cortex Visual cortex - Primary visual cortex or Striate cortex or area 17 is in the occipital lobe

Visual field disturbances 1.Right optic nerve

There is a completeanopia of the right eye.

2. Optic chiasm

Bitemporal hemianopia

3. Right optic tract

Left eye Right eye

Left homonymous hemianopia

Left eye Right eye

Pupillary Light Reflex pathway

• Information goes in on cranial nerve II (optic nerve)and comes out on cranial nerve III (oculomotor nerve). This is a consensual (both eyes are involved) parasympathetic reflex. If only the eye illuminated constricts then there is damage to the crossing fibres, i.e. damage in the midbrain.

Pupillary Light ReflexWhen light is shined into one eye causes both pupils to constrict Direct light reflex is the response of pupil constricts in the stimulated eye.Consensual light reflex is the response of pupil constricts in the unstimulated eye.

Parasympathetic innervation:• Sphincter pupillae muscle,• Ciliary muscle for near vision accommodation.

Sympathetic innervation:• The dilator pupillae muscle.• Muller's muscles of both upper and lower eyelids.• Blood vessels vasomotor tone.

Oculomotor Nerve ; Visceral MotorComponent, Accomodation Reflex (Near Reflex)

The accommodation pathway Iincludes the optic pathways from the eye to the cerebral cortex; mediated by cerebral cortex. This reflex involves the following:

1. Contraction of the ciliary muscle -increase in the curvature and therefore the refractive power) of the lens

2. Pupillary constriction to help sharpen the image on the retina

3.Convergence of the eyes to fixate on the target object (image falls on both

foveas).

Applied anatomy• Optic disc edema & Papilledema Papilledema is edema or swelling of the optic disc (papilla),

most commonly due to an increase in Intracranial pressure• Color blindness • Retinoblastoma This is a highly malignant tumour developing in the retina of a

baby or infant. A swollen optic disc and blood vessel constriction

Applied anatomy Cont.

• Three of the leading causes of blindness, from retina damage, are

- Retinitis Pigmentosa (hereditary disease of the retina for which there is no cure at present)

- Macular Degeneration and - Diabetic Retinopathy

AMD (age related macular degeneration)It is the most common cause of blindness above 65 years of age. Two general types: dry, which is more common, and wet; buildup of visual pigments in the retinaWet macular degeneration In which abnormal new blood vessels grow under the retina and leak fluid and blood.Dry macular degenerationThe most common form of macular degeneration.The Retinal pigment epithelium (RPE) gets rid of waste products produced by the photoreceptor cells. As age, the RPE can sometimes lose its ability to process this waste. Deposits of this waste yellow depositions in Bruch’s membrane (layer of choroid), called drusen, can distort and damage the retina called dry macular degeneration.

Wet macular degeneration

Dry macular degeneration

Wet macular degeneration

• Posterior vitreous detachment (PVD)

The separation of the vitreous humor from the retina due to gradual liquification, with age, of the gel-like vitreous substance.

• Retinal detachment (RD)Separation of the retina from the underlying pigment epithelium. Often initiated by a retinal tear resulting in the seepage of vitreous fluid underneath the retina; often requires immediate surgical repair.

Vitreous

Retina

Front of eye

The three fluid chambers of eye

52The anterior segment

The three fluid chambers of eye:1. Anterior chamber - Between the cornea and iris, containing aqueous humor that helps maintain shape of eyeball and supplies oxygen and nutrients to lens and cornea.

2. Posterior chamber - Between the iris and the lens, containing aqueous humor

3. Vitreous chamber - Between the lens and the retina, containing the more viscous, vitreous humor

▪ Act as a refractive medium ▪ Help to maintain the retina in place against the eye wall to prevent retinal detachment ▪ Maintain eye shape

♦ Anterior segment ▪ Anterior chamber ▪ Posterior chamber

♦ Posterior segment ▪ Vitreous chamber

The posterior segment

Patellar fossa

Refractive media: The four refractive media associated with the eyeball from anterior to posterior are:

1. Cornea 2. Aqueous humor within anterior and posterior

chambers of the eye 3. Lens 4. Vitreous humor or body

Aqueous humour production and elimination

Aqueous humour is a clear, colourless fluid, It is secreted from the ciliary processes of the ciliary body.It is secreted into the posterior chamber pupil anterior chamber canal of Schlemm which carries it into the venous system.Schlemm's canal (sinus venosus sclerae)- These canals are located around the perimeter of the iris; an endothelial-lined circumferential, venous channel filled with aqueous humour.

Zonule

CorneaIris Schlemm canal

Ciliary processes

Ant. chamber

Applied anatomy

Closed-Angle Glaucoma –

usually unilateral

- The angle formed by the

cornea and the iris

narrows

- In extremely narrow

angles, resistance to fluid

flow could lead to

increased pressure behind

the iris in the posterior

chamber. This can result in

further narrowing of the

angle or even total closure,

leading to dangerously high

intraocular fluid pressure.

Site of damage = lamina

cribosa (squash axons;

peripheral axons die first)

BLOCKED ANGLE

Applied anatomy

Open-angle glaucoma- usually bilateral due to blockage

of the trabecular meshwork. As the ciliary body continues

to produce aqueous, the fluid pressure begins to build up

in the eye. This can lead to damage of the optic nerve.

Glaucoma. The increased

pressure causes

compression of the retina

and the optic nerve which

can eventually lead to

nerve damage. Glaucoma

can cause partial vision

loss, with blindness as a

possible eventual outcome.

Muscles of the eyeball and eyelids

Levator palpebrae superioris

Superior Rectus m

Lateral rectus m

Inferior oblique m

Inferior rectus m

Medial rectus m

Superior oblique m

Muscles of the eyeball and eyelids

1.Extraocular muscles of eyeball (striated skeletal muscle)

2. Intraocular muscles of eyeball (smooth muscle) ▪Sphincter pupillae - pupillary constriction parasympathetic Innervation ▪ Dilater pupillae - pupillary dilation; sympathetic innervation▪ Ciliary muscle - accomodation; parasympathetic innervation

3.Muscles of the eyelids ▪ Orbicularis oculi (CN VII) ▪ Levator palpebrae superioris (CN III & sympathetic N)

Levator palpebrae superioris muscle

Origin: lesser wing of sphenoid bone, superior and anterior to optic canal Insertion: Tarsal plate and skin of upper eyelid Action: Elevation of upper eyelid Innervation: ▪ The superior fibres - oculomotor nerve ▪ Smooth muscle component (superior tarsal muscle/Muller’s muscle ) - sympathetic N

The upper eyelid

Roof Levator palpebrae superioris m

Muller’s muscle

Orbital septumPre- aponeurotic fat

Tarsus

Levator aponeurosis

Extrinsic or Extraocular MusclesThe muscles are situated on the outside of the eyeball. There are 4 recti and 2 oblique extraocular muscles.1. Four rectus muscles (superior, inferior, lateral & medial) a.Origin: common tendinous ring/annulus of Zinn: a fibrous tendon at the apex of the orbital cavity. b.Insertion: sclera

5.5 mm

6.7 mm

6.9 mm

7.4 mm

Spiral of Tillaux The rectus muscle pass through tenon’s capsule and insert into the sclera.The muscles insert at different distances from the cornea. The insertion pattern is a spiral known as Spiral of Tillaux.

Optic canal

Superior rectusMedial rectus

Inferior oblique

Lateralrectus m

Superior oblique

Trochlea

Inferior rectus

Commontendinous ring

Inferior oblique

Origin: maxillary floor of orbit (Unlike the other muscles of the eyeball, has its origin in the front of the orbit). Insertion:sclera, deep to inferior rectus muscle

Superior oblique muscle Origin: body of sphenoid bone, above optic canalInsertion: tendon passes through (fibrous loop on the superior medial wall of the orbit) trochlea & inserts to sclera deep to superior rectus muscle Levator palpebrae

superioris m

Actions of six extraocular muscles:

Complex due to the difference between the orbital axis and the optic axis

Axis of movements of the eyeball

1.Vertical axis: adduction/abduction (nasal & temporal displacements)2.Horizontal axis: elevation / depression3.Saggital axis (visual axis, antero - posterior axis): Intorsion / extorsion (nasal &temporal rotations of the superior cornea)

Actions of six extraocular muscles

I. Rotation about the vertical axis: adduction/abduction1. Lateral rectus: abduction Medial rectus: adduction

2. Superior and inferior rectus attach medial to the vertical axis & are thus adductors

3. Superior and inferior oblique attach posterolateral to the vertical axis and are hence abductors

II Rotation about the horizontal axis:elevation/depression1.Superior and inferior rectus both attach anterior to the horizontal axis - elevation and depression, respectively

2. Superior oblique attaches posterior to the horizontal axis and thus draws the posterosuperior surface anteriorly - hence, depression

3. Inferior oblique attaches posterior to the horizontal axis and thus draws theposteroinferior surface anteriorly - hence, elevation

III Rotation about the sagittal axis: Medial rotation (intorsion) vs. lateral rotation (extorsion) -Passes through the centre of pupil and and fovea centralis posteriorly.

1.Superior rectus and superior oblique pull the superior surface medially, hence producing intorsion.

2. Inferior rectus and inferior oblique pull the inferior surface medially, hence producing extorsion.

Actions of the extraocular muscle ActionsMuscle Innervation Primary Secondary Tertiary function function function

Medial rectus CN III Adduction -- -- Lateral rectus CN VI Abduction -- -- Superior rectus CN III Elevation Intorsion Adduction Inferior rectus CN III Depression Extorsion Adduction Inferior oblique CN III Extorsion Elevation Abduction Superior oblique CN IV Intorsion Depression Abduction

Movements from secondary position of the eyes

■ When a force acts along an axis, movement occurs only in the direction of that axis.■ If a force acts at a right angle to an axis no movement is

possible in the direction of that axis.

Relationship bet the line of muscle movement & Fick’s axes when the eye is in a secondary position.

Superior rectus muscle A. The eye is adducted (67 degrees )– no elevationB. The eye is abducted (23 degrees) from primary position– putting the plane of the muscle parallel to the Y- axis causes only elevation.

Superior oblique muscle A. The eye is abducted (35 degrees) – can’t cause depressionB. The eye is adducted (55 degrees) - depression

Superior rectus m

Superior oblique muscle

Depression

Elevation

Adduction

Abduction

MR = Medial Rectus SR = Superior Rectus SO = Superior Oblique LR = Lateral RectusIO = Inerior ObliqueIR = Inferior Rectus

Cardinal position of gaze

Cardinal positions of gaze- up/right - down/left - right - left - down/right - up/left

SR IO SR/IO SR/ IO IO SR

IR/SO SO IR

CONVERGENCE

Vertical upward movementSup rectus and inf obliqueSup rectus - turns the eye up &in Inf oblique - up & outCombined action - vertical upward movement

Vertical downward movementInf rectus and sup obliqueInf rectus- turns the eye down & inSup oblique – down & outCombined action – vertical downward movement

Clinical test or function of the extraocular muscles

■ Superior & Inferior obliqueAdduct the eye or turn the gaze inward toward the nose. Now the sup and inf recti are not able to do any elevation or depression, so only sup oblique can depress the gaze, and only inf oblique will turn the gaze upward.

■ Superior & inferior rectiElevating & depressing action of Sup & inf recti are bestdemonstrated when the eye is turned out. Oblique muscles can’t do their actions of elevation and depression.

Cranial nerve innervation of the ocular structures

1. General sensory: supplied by branches of trigeminal nerve V; mainly ophthalmic division V1, some maxillary division V22. Motor: 3 motor nerves to its muscles (CN III, IV, VI) (LR6, SO4, Remainder 3)

Nerve supply of the extraocular muscles LR6(SO4)3.That is, the lateral rectus (LR) is innervated by C.N. 6, the superior oblique (SO) is innervated by C.N. 4, and the remaining muscles (MR, SR, IR, and IO) are innervated by C.N. 3.

a. Oculomotor n. (CN III) 1. Superior division: Superior rectus, levator palpebrae superioris 2. Inferior division: medial rectus, inferior rectus, inferior obliqueb. Trochlear n. (CN IV): superior obliquec. Abducens n. (CN VI): lateral rectus

Cranial Nerve IV (Trochlear nerve)-innervates the superior oblique muscle Cranial Nerve VI (Abducens nerve) innervates the lateral rectus muscle

Trochlear nerve

Abducens nerve

Oculomotor nerve, somatic motor component, final innervation

Orbital blood supply

Opthalmic artery: A branch of internal carotid just anterior to cavernous sinus pass through the optic foramen within the dural sheath of the optic nerve.

Medial Lateral

Medial palpebral

Ophthalmic veins

Superior ophthalmic vein - passes through superior orbital fissure to drain into the cavernous sinus. Inferior ophthalmic vein - passes through inferior orbital fissure and drains into pterygoid plexus, superior ophthalmic and cavernous sinus.Veins of the same name of the orbital artery drain to the vortex vein (veins of the choroid) posterior ciliary vein ophthalmic vein cavernous sinus.

Vortex veins

The veins of the choroid

Pterygoid plexus

Applied anatomy

• Veins in the orbit communicate with facial veins and with the cavernous sinus. Thus, facial infections may lead to infection of the cavernous sinus, which may be a lethal complication.

Nerve damage

A. Abducens nerve (VI) damage causes Medial Strabismus ‑(cross eyed) /‑ medial squint

B. Trochlear nerve (IV) damage results in inability to turn eye ‑down and out.

C. Oculomotor nerve (III) damage causes: ‑ ▪ Ptosis (drooping lid from paralysis of skeletal component of

Levator palpebrae superioris)

▪ Lateral strabismus (wall eyed, from damage to Medial ‑ rectus)

▪ Dilated pupil (from paralysis of Constrictor pupillae) and

▪ Loss of accomodation

The Ocular Adnexa

The adnexa includes the eyelids, conjunctiva and lacrimal system. These structures provide both physical protection as well as immunological defence of the ocular surface.

EyelidsSkin The eye lids are made of very thin skin that contains numerous small hairs, sebaceous glands,

and sweat glands. Follicles of

eyelashes are associated with

sebaceous glands. Tarsal portion – contains the tarsal plate Orbital portion

Canthus: Medial and lateral. The two corners of the eye, where the upper and lower eyelids meet.

The normal resting position of the eyelids

Eyelids• Skin• Orbicularis oculi• Areolar tissue• Tarsal plate• Palpebral conjunctiva

Tarsal plateThe tarsal plate is a dense connective tissue which imparts support and structure to the lid. It contains numerous specialized sebaceous glands called the Meibomian glands.

To remove the foreign bodies on the conjunctival surface of the tarsus must evert the upper lid, using the upper border of the tarsus as the fulcrum.

. The tarsal glands seen from the innersurface of the eyelids

Glands of eyelids A. Tarsal or Meibomian glands (sebaceous gland) Location - tarsal plates Duct openings - on lid margin Secretion – sebum Functions - Serves as lubricant between eyelid and cornea; slow down evaporation of the middle, watery, tear layer B. Glands of Zeis (sebaceous gland)Location - eyelash follicleSecretion - sebum Function - keeps eyelashes flexible C. Glands of Moll - apocrine sweat glands at the margin of the eyelidD. Accessory lacrimal glands of Krause (in the fornix of the conjunctiva) and Wolfring (just above the tarsal plate)

Obstruction of sebaceous glands called a sty (hordeolum).

Fascias and ligaments of the orbit• Periorbita (periosteum of the orbit) Expansions – orbital septum, fibrous pulley & lacrimal fascia• Fascia bulbi or Tenon's capsule• Medial & lateral check ligaments• Suspensory ligament of Lockwoodthe eye

The right eye in sagittal section, showing the

fascia bulbi (capsule of Ténon)

(semidiagrammatic)

Tenon's Capsule (or)

Fascias and ligaments of the Orbit Cont.

Fascia bulbi or Tenon's capsule- A thin fascial membrane, envelops the eyeball from the optic nerve to the

corneoscleral junction (limbus), separates it from the orbital fat, and forms a socket

- The fascial sheath is perforated by the tendons of the extraocular muscles and reflected onto each of them

- Important in supporting the eye. A cup is formed when the eye is removed and this serves as a convenient receptacle for a prosthesis eyeball, a sheath of fascia surrounds them too.

- Fascia around the inferior oblique becomes thickened and attaches laterally to the wall of the orbit and is called the suspensory ligament. It is slung like a hammock below the eye; provides sufficient support for the eye such that, even when the maxilla forming the floor of the orbit is removed, the eye will retain its position.

- The fascias of the medial and lateral rectus muscles fan out to form medial

and lateral check ligaments attached to the lacrimal and zygomatic bones

Orbital relations with the paranasal sinuses

a. Ethmoid – medially b. Frontal – superiorly

c. Sphenoid - apex d. Maxillary - inferiorly

Fracture of the roof of the orbit may result in leakage of CSF

into the orbit.

Side view

Coronal section

Conjunctiva

- Thin translucent mucous membrane that starts at the limbus - Statified columnar epithelium 3-7 layers thick, never keratinized normally; contains goblet cells that secrete the mucin layer of the tear film - The stroma of the bulbar conjunctiva contains the accessory lacrimal glands of Krause and Wolfring1.Palpebral conjunctiva: conjunctiva covering eyelid. 2.Bulbar conjunctiva: conjunctiva covering eyeball. 3. Fornix: where the bulbar and palpebrae conjunctiva meet. Superior conjunctival fornix Inferior conjunctival fornix (Superior & Inferior limit of conjunctival layer, between eyelid and eyeball. 92

The conjunctiva is so richly supplied with blood vessels that a pale palpebral conjunctiva might signify the presence of anaemia.

Subconjunctival hemorrhage- minor trauma (cough, sneeze, or direct blow), a bleeding disorder

Lacrimal Apparatus: is made up of lacrimal gland, ducts, and canaliculi.

Flow of tears Lacrimal gland lacrimal ducts lacrimal canal nasolacrimal duct nasal cavity

Parasympathetic: stimulate secretion♦ Preganglionic parasympathetic fibers arise from CN VII.♦ Postganglionic parasympathetic fibers arise from pterygopalatine ganglion.

Sympathetic: vasoconstriction; inhibit secretion ♦Superior cervical sympathetic ganglion

Lacrimal ducts

Lacrimal gland

Any Questions?

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