Study Notes on the Orbit and Eye Muscles

Introduction to the Orbit and Its Contents

  • Subject Title: BDS1040 - The Orbit and Its Contents, Eye Muscles, Eye Movements
  • Date: 16/02/2026
  • Institution: New Giza University, School of Dentistry

Objectives of the Course

  • Identify the bones of the orbit
  • Identify the extrinsic muscles of the orbit and explain their actions
  • Describe the structures supplied by the III, IV, V, and VI cranial nerves in the orbital cavity
  • Describe the blood supply to the retina and the choroid
  • List the peripheral autonomic nerves involved in accommodation and lacrimation

Anatomical Overview of the Orbit

Orbital Volume

  • Shape: The orbit resembles a four-sided pyramid
  • Axis Orientation:
      - Long axis of each orbit passes backwards and medially
      - Medial walls are parallel
      - Lateral wall extensions form a right angle

Orbital Dimensions

  • Width: 24 mm
  • Height: 18 mm
  • Depth: 22 mm
  • Angles: 90°, 22.5°, and 122.5°

Bone Elements of the Orbital Cavity

  • The orbital cavity is formed by the following bones:
      - Frontal
      - Ethmoid
      - Lacrimal
      - Sphenoid
      - Zygomatic
      - Maxilla
      - Palatine

Detailed Bone Structure of the Orbit

  • Coronal suture: Connects the frontal and parietal bones
  • Various bones involved:
      - Frontal
      - Parietal
      - Nasal
      - Sphenoid
      - Ethmoid
      - Lacrimal
      - Zygomatic
      - Temporal
      - Maxilla
      - Mandible
      - Inferior nasal concha, vomer, alveolar margins

Orbital Walls Formation

Orbital Roof
  • Formed by:
      - Orbital plate of the frontal bone
      - Lesser wing of the sphenoid bone
  • Notable Features:
      - Lacrimal fossa
      - Fovea trochlearis
Medial Orbital Wall
  • Formed by four bones:
      - Frontal process of the maxilla
      - Lacrimal bone and fossa
      - Orbital plate of the ethmoid
      - Lesser wing of the sphenoid
Orbital Floor
  • Formed by three bones:
      - Maxillary
      - Palatine
      - Orbital plate of the zygomatic
      - Notable Feature: Infraorbital groove
Lateral Orbital Wall
  • Formed by two bones:
      - Zygomatic
      - Greater wing of the sphenoid
      - Note: This is the thickest and strongest wall

Passages from Cranium to Orbit

  1. Superior Orbital Fissure:
       - Located between the greater and lesser wings of the sphenoid
  2. Inferior Orbital Fissure:
       - Lies between the orbit floor and lateral wall, formed by sphenoid, maxillary, and palatine
  3. Optic Foramen (Optic Canal):
       - Bounded by the two roots of the lesser wing of sphenoid

Nerves and Vessels in the Orbit

Structures Passing from Superior Orbital Fissure

  • Nerves arranged from lateral to medial:
      - Lacrimal nerve
      - Frontal nerve
      - Trochlear nerve
      - Superior division of III (Oculomotor)
      - Nasociliary nerve
      - Inferior division of III (Oculomotor)
      - Abducent nerve (VI)

Contents of the Orbit

  1. Eyeball
  2. Fasciae and Fat
  3. Muscles of the Eyeball:
       - Intrinsic Muscles:
         1. Constrictor of the pupil (constrictor pupillae)
         2. Dilator of the pupil (dilator pupillae)
         3. Ciliary muscle
       - Extrinsic Muscles:
         1. Four recti muscles (superior, inferior, medial, lateral)
         2. Two oblique muscles (superior and inferior)
         3. Levator palpebrae superioris (the eyelid muscle)
  4. Nerves:
       - Sensory:
         1. Optic nerve
         2. Branches of the ophthalmic nerve (lacrimal, frontal, nasociliary)
         3. Zygomatic nerve
       - Motor: Oculomotor, Trochlear, and Abducent nerves
       - Autonomic: Sympathetic and parasympathetic
  5. Vessels:
       - Ophthalmic artery
       - Superior and inferior ophthalmic veins
  6. Lacrimal apparatus

Extrinsic Muscles of the Eye

  • There are six extrinsic eye muscles that allow the movement of the eyeball in nearly any direction, and one muscle that moves the upper eyelid.
  • Origin: All six originate from a tendinous ring around the optic nerve and insert into the sclera of the eyeball.

Types of Extrinsic Muscles

Recti Muscles (4)
  1. Superior Rectus
  2. Inferior Rectus
  3. Medial Rectus
  4. Lateral Rectus
Oblique Muscles (2)
  1. Superior Oblique
  2. Inferior Oblique
  3. Levator Palpebrae Superioris
Nerve Supply of Extraocular Muscles
  • Oculomotor Nerve (III): Supplies all muscles except for:
      - Superior Oblique (SO): Supplied by Trochlear Nerve (IV)
      - Lateral Rectus (LR): Supplied by Abducent Nerve (VI)
  • Oculomotor Nerve Details:
      - Superior Division: Supplies Superior Rectus + Levator Palpebrae
      - Inferior Division: Supplies Medial Rectus + Inferior Rectus + Inferior Oblique
  • Sympathetic Fibers: Supply Muller's muscle (smooth part of the Levator Palpebrae Superioris)

Actions and Function of Muscles

  • Possible Eye Movements:
  1. Elevation and Depression (Transverse Axis)
  2. Adduction and Abduction (Vertical Axis)
  3. Intorsion and Extorsion (Anteroposterior Axis)

Eye Muscle Actions in Different Positions

  • In an Abducted Eye:
      - Visual axis and optical axis are aligned.
      - Superior and Inferior Rectus muscles elevate and depress the eye.
  • In an Adducted Eye:
      - Visual axis aligns with direction of oblique muscle fibers.
      - Superior and Inferior Rectus muscles also elevate and depress the eye depending on the direction of gaze.

Intraocular Muscles

  • Characteristics:
      - Smooth muscles, involuntary, supplied by autonomic nerves.
  1. Constrictor Pupillae: Parasympathetic
  2. Dilator Pupillae: Sympathetic
  3. Ciliary Muscle:
       - Contracts for accommodation of the lens
       - Relaxed lens: flattened
       - Contracted lens: globular

Nerves in the Orbit

Major Nerves

  • Sensory Nerve:
      - Optic Nerve (II): Main nerve for vision, surrounded by meninges, pierced sclera to reach the brain.
      - Ophthalmic Nerve (CN V1): Branches to lacrimal, frontal, and nasociliary nerves
  • Motor Nerves:
      - Occulomotor (III), Trochlear (IV), Abducent (VI)
  • Autonomic Nerves:
      - Parasympathetic to sphincter pupillae and ciliary muscle
      - Sympathetic to dilator pupillae and Levator Palpebrae Superioris
      - Secretomotor for lacrimal gland

Clinical Considerations

Horner's Syndrome
  • Loss of sympathetic supply leading to:
      - Ptosis (drooping eyelid)
      - Miosis (constricted pupil)
      - Other symptoms: Enophthalmos, anhidrosis (lack of sweating)
      - Potential causes: Apical lung tumor
Oculomotor Nerve Lesion
  • Often due to severe head injuries
  • Symptoms include dilated and fixed pupil
Orbital Blow-out Fracture
  • Symptoms may include double vision or restricted eye movement due to inferior rectus muscle entrapment

Blood Supply of the Orbit and Eye

Ophthalmic Artery

  • Origin: Branch of the internal carotid artery
  • Course: Enters orbit through optic canal, crosses from lateral to medial
  • Branches Include:
      - Central retinal artery
      - Ciliary arteries
      - Muscular arteries
      - Medial palpebral artery
      - Lacrimal artery
      - Ethmoidal arteries
      - Supraorbital artery
      - Supratrochlear artery
      - Dorsal nasal artery
      - Long and short posterior ciliary arteries

Clinical & Functional Aspects

  • The fundus examination helps in evaluating the optic disc, macula, and overall eye health
  • Retinal and choroidal blood supply is essential for vision
  • Obstruction of fluid flow in the eye can lead to conditions such as glaucoma

Summary

  • This guide covers the essential aspects of orbital anatomy, muscular control of eye movement, and the nervous and vascular supply responsible for these functions. It outlines both the structural components and clinical implications associated with the orbit.