1. Anatomy of the Orbit and Visual Pathway
Dr Rania Gabr

2. Objectives Describe the location of the orbit.
Make a list of structures making the orbit starting from orbital margin.
Define each component.
Describe openings into orbital cavity..
Describe muscles of the orbit, their cone arrangement, origin, insertion, nerve supply and their function.
Describe the visual pathway

3. Bony Orbit Seven bones make up the bony orbit: Frontal Zygomatic
Maxillary
Ethmoidal
Sphenoid
Lacrimal
Palatine

4. The basic shape of the orbit is a pyramid
The medial walls are parallel
The depth is 1.5 x base

5. Orbital Roof Formed of : 1-orbital plate of the frontal bone, and
2- lesser wing of the sphenoid bone.

6. Medial Orbital Wall
Then medial wall of the orbit is formed from four bones:
1-Frontal process of maxillary
2-Lacrimal bone
3-Orbital plate of ethmoid
4-Lesser wing of sphenoid
Lacrimal fossa

7. Orbital Floor The floor of the orbit is formed from three bones:
Maxillary
Palatine
Orbital plate of zygomatic bone2
Infraorbital groove

8. Lateral Orbital Wall Formed from two bones: Zygomatic
Greater wing of sphenoid
Thickest and strongest

9. Orbital Foramina 1-The optic foramen
2- The supraorbital foramen, or notch
3- Nasolacrimal duct
4- Infraorbital canal
5- Inferior orbital fissure
6-Superior orbital fissure: It communicates with middle cranial fossa.

10. Main components of fissures
Superior orbital fissure: It communicates with middle cranial fossa.
It transmits
1- lacrimal nerve
2- frontal nerve
3- trochlear nerve
4-abducent nerve
5- nasociliary nerve, and
6- superior ophthalmic vein.
Inferior orbital fissure : communicates with pterygopalatine fossa.
1-maxillary nerve and
2- its zygomatic branch,
3-inferior ophthalmic vein, and
4-sympathetic nerves.

11. Optic canal:
It communicates with middle cranial fossa.
It transmits optic nerve and ophthalmic artery.
Supraorbital notch (Foramen) for supraorbital nerve and blood vessels.
Infraorbital groove and canal for infraorbital nerve and blood vessels.
Nasolacrimal canal communicates with inferior meatus of nose & transmits the nasolacrimal duct.

12. Blood Supply of the orbit
Ophthalmic Artery:
The ophthalmic artery is a branch of the internal carotid artery.
Branches:
The central artery of the retina.
The muscular branches
The ciliary arteries
The lacrimal artery
The supratrochlear and supraorbital arteries

13. Ophthalmic Veins:
The superior ophthalmic vein communicates with the facial vein .
The inferior ophthalmic vein communicates through the inferior orbital fissure with the pterygoid venous plexus.
Both veins through the superior orbital fissure and drain into the cavernous sinus.

14. Extra-ocular Muscles:
1-Levator palpebrae superioris
4 Recti muscles: Medial &lateral &superior &inferior
2 Oblique muscles: (superior and inferior)
NB. All muscles of the eye are supplied by the oculomotor nerve , EXCEPT LR6 + SO4

16. The Eye The adult human eye averages 24 mm in diameter
The eye reaches maximum size before puberty.
The transverse vertical diameter is less variable.

17. Eyeball The eyeball is formed of: Cornea Sclera Conjunctiva
Anterior Chamber
Iris/Pupil
Posterior Chamber
Lens
Vitreous
Choroid
Ciliary body
Retina

18. Eyelids -Responsible for: 1- tear spreading, 2- corneal nutrition
3- provides protection to cornea
4- Lashes offer additional protection
-When eye is open, the upper lid covers about 1/6th of the cornea & the lower lid just touches the limbus.
-The two lids meet each other at medial and lateral angles(or outer & inner canthi).

19. Levator palpebrae Superioris
In addition, the upper lid also contains the orbicularis oculi supplied by Facial and levator palpebrae superioris muscle (LPS) supplied by Occulomotor.
Eyelids are closed by Orbicularis oculi and opened by LPS..(Facial Palsy)
Levator palpebrae Superioris
arises from apex of the orbit inserted by three parts on:
1- the skin of lid,
2-anterior surface of tarsal plate,
3-conjunctiva of superior fornix.
Sebaceous glands (glands of Zeis) open directly into eyelash follicles.
The ciliary glands (glands of Moll) are modified sweat glands that open separately between adjacent lashes.

20. Lacrimal Apparatus The lacrimal apparatus consists of A-lacrimal gland
B-lacrimal passages:
1- Lacrimal sac
2- Lacrimal canaliculi
3- Nasolacrimal duct
“Lacrimal gland”
–consists of 2 parts
A-orbital lobe(sup.): situated in the lacrimal fossa in the outer part of the orbital roof.
B-palpebral lobe(inf.) situated above the superior fornix

21. Cornea In the center of the anterior pole of the globe.
Measures about 12 mm in the horizontal meridian
about 11 mm in the vertical(in adult)
Made up of 5 layers
Specialized Transparent Tissue
No blood vessels
Primarily responsible for refracting light : more than the lens
More nerve endings than anywhere else in the body
The only part of the eye that is transplanted from one person to another

22. Sclera Sclera is opaque and white
Covers the posterior 5/6 of the surface of the globe, with an anterior opening for the cornea and a posterior opening for the optic nerve
Called the whites of the eye
Tough, fibrous tissue: site of extra-ocular muscle attachment
Opaque...allows NO light to enter

23. Limbus The limbus is the border of the cornea and the sclera.
It is the transition zone between the peripheral cornea and the anterior sclera

24. Conjunctiva
Mucous membrane with non keratinized squamous epithelium and goblet cells
Thin, richly vascularized substantia propria
Can be divided into three geographic zones:
Palpebral
Forniceal
Bulbar

25. Anterior chamber
The anterior chamber is bordered anteriorly by the cornea and posteriorly by the iris diaphragm and the pupil
The anterior chamber is filled with aqueous humor, which is produced by the ciliary epithelium

26. Lens
It is the lesser of the two refractive elements in the dioptric system
It lacks innervation and is avascular.
Transparent, biconvex structure, held in place by ciliary zonules attached to (suspensory ligaments)
Composed of 6 layers
Refracts light
Nutrition comes from aqueous humor…
Insoluble deposits of proteins build up over time = Cataracts :A clouding of the lens and capsule

27. Uveal Tract
The uveal tract is the main vascular compartment of the eye.
It consists of three parts:
Iris
Ciliary body (located in the anterior uvea)
Choroid (located in the posterior uvea)

28. Iris
The colored part of the eye…unique to every individual like a fingerprint
Color is dependent on the amount of pigment
A diaphragm, the iris has tiny muscles :Dilator pupillae and Sphincter pupillae ,that control the light levels in the eye
Has 2 layers
Pupil is located in the center of the iris
pupil = hole: it is not an eye structure per se

29. Ciliary Body The ciliary body, is triangular in cross section.
The apex of the ciliary body is directed posteriorly.
Its base gives rise to the iris.
The only attachment of the ciliary body to the sclera is at its base, via its longitudinal muscle fibers, where they insert into the scleral spur.

30. Choroid The choroid, the posterior portion of the uveal tract,
IT nourishes the outer portion of the retina.
It averages 0.25 mm in thickness and consists of three layers of vessels

31. Vitreous
The vitreous cavity occupies four fifths of the volume of the globe
The transparent vitreous humor is important to the metabolism of the intraocular tissues because it provides a route for metabolites used by the lens, ciliary body, and retina
Its volume is close to 4.0 ml Although it has a gel-like structure, the vitreous is 99% water

32. Fundus
The fundus is the part of the eye that is visible on ophthalmoscopy, including the retina and its vessels and the optic nerve head (or optic disc)
The macula Lutea, 5–6 mm in diameter.
At the macula's center lies the fovea, rich in cones and responsible for color vision and the highest visual acuity.
It is the Point of sharpest vision

33. Retina Most internal layer of eye, facing the vitreous
Converts light energy into electrical energy which is then sent to the brain via the optic nerve
Actually an extension of brain tissue
Composed of 10 layers
It consists of:
Outer pigmented layer.
Inner nervous layer(retina proper) which consists of many layers but most important are:
Rods & cones
Bipolar cells
Axons of ganglion cells
Blind spot

34. Optic Nerve
Axons of retinal ganglion cells converge at the optic disc and pass into optic nerve.
Then the nerve passes posteromedially in the orbit, exits through the optic canal to enter the middle cranial fossa to joins the optic chiasma.

35. Optic Chiasma
Fibers from the nasal (medial) half of retina decussate within the chiasma and join uncrossed fibers from the temporal (lateral) half of the retina to form the optic tract.
The decussation of nerve fibers in the chiasma results in the right optic tract conveying impulses from the LEFT visual field and vice versa.
The partial crossing of optic nerve fibers in the optic chiasma is a requirement for binocular vision.
Damage to the optic tract or more central parts of the pathway tend to cause comparable visual deficits in both eyes

36. Optic Tract
Each optic tract contains ipsilateral temporal and contralateral nasal fibers from the optic nerves .

37. Lateral geniculate body
Optic Tracts
Fibers in the optic tracts:
Mainly terminate in the lateral geniculate bodies of the thalamus
A few fibers terminate in pretectal area and superior colliculus. These fibers are related to light reflexes
Lateral geniculate body

38. Optic radiations
The optic radiations connect the lateral geniculate body with the cortex of the occipital lobe
The fibers of the optic radiations leave the lateral geniculate body and run around the temporal horn of the lateral ventricle, approaching the anterior tip of the temporal lobe (the so-called loop of Meyer)

39. Optic Radiation
Optic radiation or thalamocortical or geniculocalcarine fibers originating in the lateral geniculate nucleus.
Passes through the retrolenticular part of the internal capsule to the visual cortex above and below the calcarine sulcus. (area 17 of Brodmann's)

40. Visual Pathway Cones Bipolar neurons
Ganglion cell’s axon forms the optic nerve
Optic nerve to the Optic Chiasm
Optic tract
Lateral geniculate nuclei of the thalamus
Optic Radiations
Primary visual areas of the occipital lobes

41. Visual Pathway 3 neuron pathway Photoreceptors: Rods & Cones of retina
1st order neurons:
Bipolar cells of retina.
2nd order neurons:
Ganglion cells of retina. Their axons form the optic nerve
3rd order neurons:
Neurons in the lateral geniculate body. Their axons terminate in primary visual cortex.

42. A lesion of both visual cortices causes a complete blindness.
Visual Field Deficits
Cut at level :1. A lesion of the right optic nerve causes a total loss of vision (blindness) in the right eye
Cut at level :2. A lesion of the optic chiasma causes a loss of vision in the temporal half of both visual fields: bitemporal hemianopia.
Cut at level: 3 & 4. A lesion of the right optic tract & right optic radiation just after the LGN causes a loss of vision in the left hemifield: contralateral homonymous hemianopia.
A lesion of both visual cortices causes a complete blindness.