Anatomy of Eye, adnexa & orbit in a Nutshell

Anatomy of Eye, Adnexa & Orbit:

• Shape: Pyramidal shaped
• Dimension: Twice as deep as wide
• Orientation: 45-degree angle between orbits
• Eyeball occupies only the anterior half
• Lots of fat & blood vessels
  • Functions of the orbital fat:
    • Shock absorber, cushion
    • Lubrication, fluid movement →Semiliquid fatty pad allows eyeball to spin
    • Protect nerves, vessels
    • Last place that fat pads will disappear in body (when fat pads disappear→sunken cheek and eyes)
• Walls of the orbit (7 elements): not smooth, full of holes and grooves

• • Floor: maxilla, zygomatic, palatine
  • Medial (fragile bone, paper thin): ethmoid, lacrimal, frontal
  • Roof: frontal, sphenoid
  • Lateral: zygomatic, sphenoid

Orbital foramina & Fossae

• Optic canal holds optic nerve and ophthalmic artery
• Superior orbital fissure: CN III, IV, V¹, VI, ophthalmic veins
  • Ophthalmic veins communicate w/ cavernous sinus and facial vein
• Inferior orbital fissure: CN V² from foramen rotundum
• Both orbital fissures make V shape lateral to optic canal
• Anterior & posterior ethmoidal formina: Anterior & posterior AV & nerves pass through these foramina on the medial wall
• Fossa for lacrimal sac of the superior wall
• Fossa for nasolacrimal canal (inferomedial)
  • Canal contains duct→lacrimal fluid from surface of eye into nasal cavity
  • Communication between orbit and nasal cavities

Lacrimal gland

• Superolateral part of orbit
• Sensory: V¹
• Secretary motor: pteryogoid ganglion of facial nerve
• Produces tears: blinking of eyes causes movement to keep eyes moist
  • Brings fluid from lateral corner to medial corner
• Drainage of tears: lacrimal gland→canals→conjunctival sac on surface of eyeball→surface of eye→lacrimal papillae with puncta (holes)→canaliculae→lacrimal sac→nasolacrimal duct
  • Conjunctiva: mucosa that covers eyelid and goes onto sclera of eye
    • Rich with blood vessels
    • Gets inflamed during drinking and when particles touch it
• Nasolacrimal duct becomes saturated→crying→nose runs when cry

Eyelids: Protective skin flaps

• Tarsus (superior and inferior): of dense connective tissue plates
• Tarsus contains tarsal glands (mybomium glands)
  • Glands open up on inner surface of eyelid
  • Glands secrete lubricating liquid to keep eye moist and eyelids from sticking together
  • Under hormonal control; sebaceous glands
  • Duct can get clogged→get growth
• Ciliary glands associated with eyelashes (cilia): superficial
  • Under hormonal control; sebaceous glands
  • When clogged→stye
• Muscles
  • Levator palpebrae superioris
    • Inserts on tarsus superior (dense fibrous band) and goes deep and b/w orbicularis oculi
    • Assisted by superior tarsal muscle (sympathetic trunk)
    • CN III
  • Obicularis oculi
    • Forceful and passive closure of eye
    • Closing helps moisten cornea and protect from outside particles to prevent inflammation and blindness
    • CN VII
• Common lesions
  • Third nerve palsy: affects superior division of oculomotor
    • Ptosis: drooping of eyelids
    • Mild version: sympathetics to upper eyelid affected
  • Bell’s palsy (CN VII)

Eyeball: Hollow Sphere

• 3 coats

• • Fibrous outer coat
    • Sclera: tough, dense fibrous coat that covers 5/6 of eyeball
    • Cornea: continuous with sclera, transparent
  • Vascular middle coat—three components are continuous
    • Choroids: highly vascularzied, most richly vascularized structure in body
    • Ciliary body: donut shaped, surrounds lens
      1. Ciliary zonule of Zinn: radial fibers from ciliary body to lens
         1. Suspends lens
         2. Works with zonular fibers—radial (suspensory ligament of lens)
         3. See more about function in accommodation of lens section below
      2. Ciliary processes projects from chillier body: produces aqueous humor
         1. Humor flows from posterior to anterior chamber thru pupil
         2. Nourishes and bathes cornea and lens (avascular)
         3. Liquid flows between iriscornea angle→venous channels (sinus venosus sclera, canal of schlemm)
            1. Channels make circle around perimeter of cornea
         4. Fluid is replenished every 90 minutes
      3. Iris: surrounds pupil (hole=aperture of camera)
         1. Controls amount of light entering by changing shape and size of pupil
         2. Contraction controlled by inferior division of oculomotor (parasymp)
            1. Goes thru ciliary ganglion
            2. Dependent on circular, concentric fibers
         3. Dilation: Sympathetic control (long ciliary nerves)
            • Dependent on radial fibers

• Neural inner coat: retina—posterior 5/6
  • Retina has two different layers: developed separately
    • Pigmented layer: fused with choroids
    • Neural layer: picks up light rays
      1. Axons of ganglion cells travel towards optic disk
      2. Connect to bipolar cells→rods and cones
    • Detached retina: separation of two layers
      1. Happens to prizefighters
    • Continuous with optic nerve at optic disk/papilla:
      1. In the middle: blind spot with no photoreceptors
      2. With the optic nerve, find vessels (arteries are branches of ophthalmic artery)
         1. Travels within dura
         2. Central artery of retina pierces dura, arachnoid, pia to enter substance of optic nerve
    • Macula lutea (lateral to optic disk): yellow spot
      1. Pit: fovea centralis—only has cones
         1. Area of acute vision

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