Clinical Anatomy of the Organ of Vision

1. The Orbit

• Maxilla, Zygomatic, Frontal, Ethmoid, Lacrimal, Sphenoid, Palatine

2. The Eyeball

3. Membranes (Walls/Tunics) of the Eyeball

A. Outer Fibrous Layer

• Sclera — covers the posterior and lateral 5/6 of the eyeball; opaque dense connective tissue (the "white of the eye"); pierced by the optic nerve posteriorly; provides muscle attachment points. The fascial sheath of the eyeball (bulbar sheath / Tenon's capsule) covers the external scleral surface between the optic nerve entrance and the corneoscleral junction.
• Cornea — covers the anterior 1/6; transparent, avascular; continuous with the sclera at the limbus; allows light entry.

B. Middle Vascular Layer (Uvea)

• Choroid — posterior 2/3 of the vascular layer; thin, highly vascular and pigmented; supplies the outer retina; firmly adherent to retina internally, loosely to sclera externally.
• Ciliary body — extends from the anterior border of the choroid; triangular ring containing:
  • Ciliary muscle — smooth muscle fibers (longitudinal, circular, radial); parasympathetic innervation via CN III; contraction loosens the suspensory ligament → lens rounds up → accommodation for near vision.
  • Ciliary processes — longitudinal ridges projecting inward; give rise to zonular fibers (suspensory ligament of the lens) and secrete aqueous humor.
• Iris — the colored diaphragm anterior to the lens; contains:
  • Sphincter pupillae — parasympathetic (CN III via ciliary ganglion); constricts pupil (miosis)
  • Dilator pupillae — sympathetic (superior cervical ganglion via long ciliary nerves); dilates pupil (mydriasis)

C. Inner Layer (Retina)

• Optic (visual) retina — posterior portion; contains photoreceptors (rods for dim light/peripheral vision; cones for color/central vision)
• Optic disc (blind spot) — where the optic nerve exits; no photoreceptors
• Fovea centralis — highest cone density; sharpest central vision
• Nonvisual retina — covers the inner surface of the ciliary body and iris anteriorly (ora serrata marks the transition)

4. Chambers of the Eye

Anterior Chamber

• Located posterior to the cornea, anterior to the iris
• Filled with aqueous humor

Posterior Chamber

• Located posterior to the iris, anterior to the lens
• Aqueous humor is secreted here by ciliary processes → flows through the pupil → anterior chamber → drains into the scleral venous sinus (Canal of Schlemm) at the iridocorneal angle
• Aqueous humor supplies nutrients to the avascular cornea and lens and maintains intraocular pressure
• Disruption → glaucoma (elevated intraocular pressure)

Postremal (Vitreous) Chamber

• The posterior 4/5 of the eyeball, from lens to retina
• Filled with the vitreous body — transparent, gelatinous; unlike aqueous humor, it cannot be replaced

Lens

• Separates anterior 1/5 from posterior 4/5 of the eyeball
• Transparent, biconvex, elastic; attached by zonular fibers to the ciliary body
• Opacity of the lens = cataract

5. Accessory Apparatus

A. Eyelids (Palpebrae)

• Skin — thinnest skin in the body; highly vascular; heals rapidly with minimal scarring
• Orbicularis oculi muscle — subcutaneous sphincter of the eyelid; innervated by temporal and zygomatic branches of CN VII (facial nerve); divided into pretarsal, preseptal, and orbital segments; also drives the lacrimal pump — contraction during blinking dilates the lacrimal sac and draws tears through the canaliculi

• Tarsal plates — dense connective tissue plates giving rigidity to the eyelids; contain tarsal (Meibomian) glands — modified sebaceous glands secreting an oily substance that reduces tear evaporation; blockage = chalazion
• Conjunctiva — thin transparent membrane lining the posterior eyelid surface, then reflecting onto the anterior sclera to the limbus; forms the conjunctival sac (superior and inferior fornices)

• Levator palpebrae superioris — raises the upper eyelid; inserts into superior tarsus and eyelid skin; innervated by CN III (oculomotor)
• Superior tarsal muscle (Müller's muscle) — smooth muscle from the inferior surface of the levator to the upper edge of the superior tarsus; innervated by postganglionic sympathetic fibers from the superior cervical ganglion. Loss of either muscle → ptosis

• Normal horizontal palpebral fissure: 28–30 mm; vertical: 9–10 mm
• Upper lid margin sits at the midpoint between superior corneal limbus and pupil
• Lower lid margin abuts the inferior corneal limbus
• Upper lid crease: 10–12 mm above lid margin in women, 7–8 mm in men

• Tarsal (Meibomian) glands — sebaceous, open onto lid margin; blockage → chalazion (inner surface)
• Sebaceous and sweat glands of the eyelash follicles — blockage → sty/hordeolum (lid edge)

B. Lacrimal Apparatus

• Located in the superolateral orbit, in the lacrimal fossa of the frontal bone
• Divided into two parts by the levator palpebrae superioris:
  • Orbital part (larger) — in the lacrimal fossa
  • Palpebral part (smaller) — inferior to the levator, in the superolateral eyelid
• Numerous ducts empty into the lateral superior conjunctival fornix
• Innervation:
  • Sensory — lacrimal branch of the ophthalmic nerve (V1)
  • Secretomotor (parasympathetic) — preganglionic from CN VII (greater petrosal nerve) → pterygopalatine ganglion → postganglionic fibers travel with the zygomatic nerve then lacrimal nerve → gland
  • Sympathetic — from superior cervical ganglion

1. Secreted laterally → spread medially by blinking
2. Accumulate in the medial lacrimal lake
3. Enter through the lacrimal puncta (one per eyelid, on the medial lid margin)
4. Travel through the lacrimal canaliculi (superior and inferior) medially
5. Enter the lacrimal sac — situated in the lacrimal fossa between the anterior and posterior lacrimal crests (posterior to the medial palpebral ligament)
6. Drain inferiorly via the nasolacrimal duct → opens into the inferior nasal meatus beneath the inferior nasal concha

Summary Table