Visual Organ

ORBITAL ANATOMY

VISUAL ORGAN

• Dr. Samsani

ORBITA FORM

• The orbit resembles a pyramid with specific orientations:
  • Base (aditus orbitae): Faces forward (facies).
  • Apex: Faces backward (canalis opticus).

Constituent Bones of the Orbit:

• Os frontale: Forms the superior part (roof).
• Os ethmoidal: Forms the medial part (lamina papyracea).
• Os sphenoidale:
  • Ala minor (roof)
  • Ala major (lateral wall)
  • Corpus (medial & apex)
• Os zygomaticum: Lateral wall.
• Os lacrimale: Medial part, near the fossa sacci lacrimalis.
• Maxilla: Forms the base (inferior part) and partly medial aspect.

ORBITA ADITUS ORBITAE

• Definition: It is the anterior opening of the orbit serving as the entrance to the orbital cavity.
• Boundaries: Defined by the orbital margin (edge of the orbit).

Composition of the Orbital Margin:

• Superior border: Frontal bone
• Inferior margin (margo inferior): Maxilla + Os zygomaticum
• Medial margin (margo medialis): Processus frontalis maxillae + Os lacrimale
• Lateral margin (margo lateralis): Os zygomaticum + Processus zygomaticus os frontale

ORBITA ORBITATIC EDGE (MARGO ORBITALIS)

• Characteristics:
  • Shape: Not a perfect circle but a spiral structure.
  • Position: It is the anterior border of the orbit (aditus orbitae).
  • Support: Strengthened by the orbital septum.

Composition Details:

• Upper anteromedial & anterolateral (margo superior): Os frontale
• Lower anteromedial & medial (inferior margin): Maxilla
• Bottom anterolateral & lateral (margo inferior): Os zygomaticum
• Special features:
  • Crista lacrimalis anterior (maxilla)
  • Crista lacrimalis posterior (os lacrimale) (\longrightarrow) Together they limit the fossa sacci lacrimalis.

ORBITA BASE (ADITUS ORBITAE)

• Location: On the surface of the facial skeleton, anterolaterally directed.
• Characteristics: It is the entrance to the orbit.
• Limits: Defined by the orbital margins (superior, inferior, medial, lateral).

APEX

• Orientation: Facing posteromedially.
• Characteristic Mark: Marked by the optic canal in the minor ala of the sphenoid bone.
• Structures Passing Through:
  • Optic nerve (CN II)
  • Ophthalmic artery

ORBITA MEDIAL WALL

• Characteristics:
  • Form: Straight and parallel to the contralateral side.
  • Separation by: Ethmoidal cells.

Constituent Bones:

• Ethmoidal bone orbital lamina (main contributor)
• Frontal process of the maxilla
• Lacrimale os
• Small part of the corpus ossis sphenoidalis

Important Note:

• Very thin wall, prone to fracture.

LATERAL WALL

• Characteristics: The thickest and strongest wall of the orbit.

Constituent Bones:

• Frontal process of the zygomatic bone
• Ala major ossis sphenoidalis

Other Relationships:

• Separates the orbit from the temporal fossa and middle cranial fossa.
• Also, it is the most exposed wall and frequently injured.

ORBITA SUPERIOR WALL (ROOF)

• Constituent Bones:
  • Pars orbitalis ossis frontalis
  • Small part of minor ala of the sphenoid bone

Important Structures:

• Fossa glandulae lacrimalis: Located anterolaterally where the lacrimal glands are situated.
• Separates the orbit from the anterior cranial fossa.

INFERIOR WALL (FLOOR)

• Constituent Bones:
  • Maxilla
  • Zygomatic bone
  • Palatine bone

Additional Relationships:

• Separates the orbit from the maxillary sinus.
• Characteristics: Thin and slopes from the apex to the base.

Important Structures:

• Sulcus infraorbitalis: Leads to the canalis infraorbitalis (pathway for infraorbital nerve).

ORBITAL FISSURES AND CANALS

SUPERIOR ORBITAL FISSURE

• Location: Connects inner cranial cavity to the orbit.
• Boundaries:
  • Medial: Corpus ossis sphenoidalis
  • Superior: Wing minor ossis sphenoidalis
  • Inferior: Medial tape of permucan orbital ala major ossis sphenoidalis

Structures Passing Through:

• N. oculomotorius (CN III)
• N. trochlearis (CN IV)
• N. abducens (CN VI)
• Branch of the ophthalmic nerve (V1)
• Vv. ophthalmicae

INFERIOR ORBITAL FISSURE

• Location: Connects the orbit to pterygopalatine and infratemporal fossa.

Structures Passing Through:

• N. infraorbitalis
• N. zygomaticus (branch of N. maxillaris / V2)
• Rami orbitales of ganglion pterygopalatinum
• Related blood vessels
• Connecting veins to pterygoid venous plexus

OPTIC CANAL

• Location: Minor ala of the sphenoid bone, towards the apex of the orbit.
• Structures Passing Through:
  • N. opticus (CN II)
  • A. ophthalmica

EYEBALL (BOLA MATA)

ACCESSORY STRUCTURES:

• Eyelids (Palpebrae)
• Conjunctiva
• Lacrimal apparatus

SUPPORTING STRUCTURES:

• Orbital septum
• Orbital fat body
• Tenon's capsule

BULBUS OCULI (EYE BULB)

LAYERS:

1. Fibrous coat:
   • Composed of cornea and sclera.
2. Tunica vasculosa:
   • Composed of choroidea, corpus ciliare, iris.
3. Tunica interna:
   • Composed of retina.

SCLERA

• Definition: The sclera is the white part of the eye, forming approximately $5/6$ of the back of the tunica fibrosa.
• Functions:
  • Protection: Shields intraocular structures from trauma.
  • Maintaining shape: Helps sustain intraocular pressure and the globular shape.
  • Muscle attachment: Serves as an attachment point for extrinsic muscles.
  • Pathways for nerves and vessels: Contains foramina for nerves and vessels leading to the retina and choroid.

FORAMEN IN THE SCLERA

• Posterior:
  • Lamina cribrosa sclerae: Site of entry for optic nerve (CN II) and passage for blood vessels (arteria centralis retinae & vena retinae).
• Anterior:
  • Connected to posterior chamber via limbus corneae and continues into the cornea.

ANATOMICAL RELATIONSHIPS

• Anterior: Connects to cornea at the limbus corneae.
• Posterior: Penetrated by optic nerve at the lamina cribrosa sclerae.
• External: Covered by Tenon's capsule (fascia bulbi).
• Internal: Related to the choroid (tunica vasculosa).

MUSCLE INSERTION SITES ON SCLERA

• Attachment points for six extraocular muscles:
  • Recti muscles: Superior, inferior, medial, lateral.
  • Oblique muscles: Superior & inferior.
• Function: Allows the eyeball to move in various directions.

CORNEA

• Location: Most anterior part of the eyeball; transparent, forming the main "window" of the eye.
• Characteristics:
  • Avascular: Lacks blood vessels.
  • Regular collagen: Maintains transparency.
  • Sensory nerve endings: Highly sensitive to stimulation.

FUNCTION OF CORNEA

• Light refraction: The primary refractive medium focusing light onto the retina.
• Protection: Shields eyeball from trauma & infection.

TUNICA VASCULOSA BULBI (UVEA)

• Definition: The middle layer of the eyeball, situated between the sclera (outer) and retina (inner).
• Main Functions:
  • Provides nutrition to the retina.
  • Regulates the amount of light entering the eye.
  • Lens accommodation (adjusting focus).
  • Produces aqueous humor (maintains intraocular pressure).

MAIN COMPONENTS:

• Choroidea
• Corpus ciliare (ciliary body)
• Iris

CHORIOIDEA

• Location: The vascular layer positioned between the sclera (outer) and retina (inner).
• Structure:
  • Rich in blood vessels, particularly fine capillaries (choriocapillaris) supplying the retina.
  • Contains melanin pigment; absorbs excess light.

CORPUS CILIARE (CILIARY BODY)

• Location: Anterior chorioidea, ring-shaped around the lens.
• Parts:
  • Pars plana: Flat and posterior.
  • Pars plicata: Folded and anterior; forms the ciliary process.
• Function:
  • Produces aqueous humor (fills anterior & posterior chambers).
  • Lens accommodation via the ciliary muscle and zonula ciliaris.
• Accommodation Mechanism:
  • Contraction of ciliary muscle → zonules relax → lens thickens → near focus.
  • Relaxation of ciliary muscle → zonules tense → lens thins → distant focus.

IRIS

• Location: The most anterior part of the uvea; thin, pigmented ring with a central opening (pupil).
• Function: Regulates the amount of light entering the retina.

Smooth Muscle Structures:

• M. sphincter pupillae (circular): Contraction → pupil shrinks (miosis).
• M. dilator pupillae (radial): Contraction → pupil dilation (mydriasis).
• Functions:
  • Regulates the amount of light entering the retina (analogous to a camera diaphragm).
  • Determines eye color through iris pigment.

TUNICA INTERNA (RETINA)

• Definition: The innermost layer of the eyeball, containing nerve cells functioning as photoreceptors (rod and cone cells).
• Function: Converts light energy into electrical impulses transmitted through the optic nerve to the brain.
• Anatomical Features:
  • Fundus oculi: Contains macula lutea, fovea centralis, and papilla nervi optici (disk of the optic nerve).

OPTIC PAPILLA (OPTIC DISC)

• Location: The nasal part of the retina where axons of ganglion cells converge to form the optic nerve.
• Structure: Lacks photoreceptors (rods or cones); appears as a pale round area on examination.
• Function:
  • Exit point for optic nerve and retinal blood vessels.
  • Clinical Conditions:
  • Papilledema: Sign of increased intracranial pressure.
  • Glaucoma: Damage to nerve fibers in the optic disc.

MACULA LUTEA

• Location: Central area of the retina, oval and yellowish.
• Structure: Rich in cone cells, few rod cells.
• Function:
  • Provides sharp vision (high visual acuity).
  • Important for reading, recognizing faces, and fine detail.
• Clinical Notes:
  • Macular degeneration: Age-related loss of central vision; peripheral vision remains intact.

FOVEA CENTRALIS

• Location: Center of the macula lutea.
• Structure:
  • Diameter: Approximately $1.5 ext{ mm}$.
  • Contains only cone cells.
  • Thin retinal layer allowing direct light access to photoreceptors.
• Function:
  • Maximum visual acuity area; highest resolution for focusing on detailed objects.
• Clinical Condition:
  • Damage to fovea results in severe loss of central vision.

POSTERIOR SPACE OF