ocular anatomy orbit & eye mbbs, india
TRANSCRIPT
1
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
3
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
5
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
6
■ 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
8
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
9
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.
1010
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
1111
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
12
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
ring
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
13
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
15
3. Inner nervous layer Retina
1616
Cornea
Pupil
Retina
Lens capsule
Anterior chamber
Posterior chamber
Macula
Fovea
Suspensory ligaments
Conjunctiva
Ora serrata
Central artery& vein of retinaCiliary body
Optic nerve
Schlemm’s canal
Iris
Lateral rectus
Medial rectus Sclera Choroid
17
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
19
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
20
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
23
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
25
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
26
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.-
30
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
33
34
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.
36
Retinal Anatomy
37
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
39
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
Left eye Right eye
44
1
23
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.
45
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.
Applied anatomy Cont.
49
Wet macular degeneration
Dry macular degeneration
Dry macular degeneration
Wet macular degeneration
50
Applied anatomy Cont.
• 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
Retina
Front of eye
The three fluid chambers of eye
51
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
53
♦ 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
55
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
Lens
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
58
59
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)
60
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
61
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.
63
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
64
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)
65
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
66
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
67
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.
68
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
70
LR LR
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
MR MR
IR SO
IR/SO
IR/SO SO IR
MR MR
CONVERGENCE
71
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.
73
74
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
Orbit
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.
78
79
Medial Lateral
1
2
3
4
56
7
Medial palpebral
8
9
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.
81
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
82
83
84
The Ocular Adnexa
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)
87
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
88
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
93
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
94
Any Questions?