Anatomy of the Eye and Orbit

ILOS

• By the end of the lecture, students should be able to describe the orbit's bones, eyeball components, differentiate eye muscles and their supplying cranial nerves, and correlate common eye conditions with their anatomical components.

Bony Orbit

• Composed of the frontal bone, lesser sphenoid wing, maxilla, zygomatic bone, lacrimal bone, and ethmoid bone.
• Contains openings for structures like optic canal, superior and inferior orbital fissures.

Eyeball

• Globe-shaped structure that fills the orbit.
• Its rounded contour is interrupted by the cornea, which is 1/6th of the eyeball's total area.

Fibrous Coat

• Composed of the sclera (posterior 5/6) and cornea (anterior 1/6).
• Sclera: Opaque, protective outer layer, providing attachment to eye muscles.
• Cornea: Transparent, allowing light to pass through.
• Both connect at the corneo-scleral junction

Vascular Coat

• Consists of the choroid, ciliary body, and iris.
• Choroid: Highly vascular pigmented layer, providing oxygen and nutrients to the eye layers and absorbing scattered light.
• Ciliary body: Triangular, ring-shaped structure, including ciliary muscle and processes which produce aqueous humor.
• Iris: Colored portion containing the pupil, regulating light entering the eye.
  • Contains sphincter pupillae (parasympathetic) and dilator pupillae (sympathetic) muscles controlling pupil size.

Nervous Coat (Retina)

• Sensitive to light, lining the posterior and internal surface of eye.
• Contains two layers: pigmented layer (outer) and neural layer (inner).
• Pigmented layer prevents light scattering.
• Neural layer contains photoreceptors, capturing light for visual signal transmission.

Anterior and Posterior Chambers

• Anterior chamber: Between the cornea and iris.
• Posterior chamber: Between the lens and iris.
• Filled with aqueous humor that is produced and drained constantly.
• Glaucoma results from increased intraocular pressure, often due to blocked drainage.
• Cataract: Lens opacity, often of old age.

Extraocular Muscles

• 6 muscles controlling eye movements.
  • 4 rectus (superior, inferior, lateral, medial)
  • 2 oblique (superior, inferior)
• They control elevation, depression, abduction, and adduction of the eyeball.
• Complex movements arise from the axis differences between the orbit and the eyeball.

Cranial Nerves

• Trochlear (IV): Supplies the superior oblique muscle.
• Abducent (VI): Supplies the lateral rectus muscle.
• Occulomotor (III): Supplies most extraocular muscles (except lateral rectus and superior oblique) and also some muscles of the eyelid.
• Nerve damage leads to visual and eyelid movement impairment (e.g., ptosis).