Sense Organs 1: Eye Anatomy

Sense Organs 1: Eye

• The eye is a sense organ.
• By the end of the lecture, students should be able to describe the bony orbit, identify contents of the orbital cavity, and describe extraocular muscles.

Orbital Cavity

• It's a pyramidal space with a base, apex, and four walls.
• Roof: Orbital plate of frontal bone
• Floor: Orbital surface of maxilla, zygomatic bone
• Medial wall: Lacrimal bone, orbital plate of ethmoid bone
• Lateral wall: Zygomatic bone, greater wing of sphenoid bone

Contents of the Orbital Cavity

• Eyeball
• Muscles
• Blood vessels
• Nerves
• Ciliary ganglion
• Lacrimal gland
• Orbital fat

Muscles of the Orbit

• Extrinsic muscles: Control eye movement
  • 4 Recti muscles (superior, inferior, medial, lateral)
  • 2 Oblique muscles (superior, inferior)
• Intrinsic muscles: Control pupil size.
  • Dilator pupillae
  • Constrictor pupillae
  • Ciliary muscle

Extraocular Muscles

• Origin: Common tendinous ring
• Insertion: Sclera anterior to coronal equator of eyeball
• Action: Move the cornea vertically or horizontally (according to muscle name and function)
• Nerve supply: Different muscles are supplied by different nerves (see below)

Superior Oblique Muscle

• Origin: Roof and medial surface of the orbit.
• Insertion: Sclera, posterior to the coronal equator.
• Action: Depression, abduction, and intorsion.
• Nerve supply: Trochlear nerve

Inferior Oblique Muscle

• Origin: Anterior part of the floor of the orbit.
• Insertion: Sclera, posterior to the coronal equator.
• Action: Elevation, abduction, and extorsion.
• Nerve supply: Inferior division of oculomotor nerve

Levator Palpebrae Superioris (LPS)

• Origin: From orbital surface of the roof, anterior superior to optic canal.
• Insertion: Skin of upper eyelid, superior tarsus (Müller's muscle), and superior fornix of conjunctiva.
• Action: Elevates upper eyelid.

Actions of Extraocular Muscles

• Movement around three axes (transverse, vertical, anteroposterior).
  • Transverse: Elevation and depression
  • Vertical: Abduction and adduction
  • Anteroposterior: Intorsion and extorsion.

Nerve Supply of Extraocular Muscles

• All extraocular muscles are supplied by the oculomotor nerve, except the superior oblique and lateral rectus
• Superior oblique: Trochlear nerve
• Lateral rectus: Abducent nerve
  • Other extraocular muscles: Oculomotor nerves (superior and inferior divisions)

Applied Anatomy (Cranial Nerve lesions)

• Cranial nerve 3 lesion: Ptosis, lateral squint, loss of accommodation, dilated pupil, slight proptosis, diplopia.
• Cranial nerve 6 lesion: Medial squint, diplopia.

Intraocular Muscles

• Formed of smooth muscle fibers.
• Have involuntary actions.
• Supplied by autonomic nerves (sympathetic and parasympathetic)
• Include 3 muscles:
  • Constrictor pupillae (parasympathetic)
  • Dilator pupillae (sympathetic)
  • Ciliary muscles (parasympathetic)

Blood Vessels of the Orbit

• Ophthalmic artery: A branch of the internal carotid artery that enters the orbit through the optic canal.
• It supplies the orbit through several branches.
  • Supraorbital artery, Dorsal nasal artery, Lacrimal artery and Central retinal artery.
  • Fore head, medial and posterior ethmoidal, and branches to orbit.

Ophthalmic Veins

• Superior ophthalmic vein: Receives tributaries, passes through superior orbital fissure, and ends in cavernous sinus. Communicates with supraorbital and angular veins.
• Inferior ophthalmic vein: Begins at the anterior part of the orbit floor, passes through the superior orbital fissure, and ends in the cavernous sinus. Communicates with the pterygoid plexus.