EYES

• Anterior pole of the eye


  The center of the cornea or the center of the pupil
• Eye movements


  • Elevation
  • Depression
  • Abduction
  • Adduction
  • Medial rotation
  • Lateral rotation
• Extrinsic eye muscles


  • Superior rectus
  • Inferior rectus
  • Medial rectus
  • Lateral rectus
  • Superior oblique
  • Inferior oblique
• Actions of superior and inferior recti

  1. Raise cornea

  2. Depress cornea

  3. Rotate cornea medially
• Actions of superior and inferior oblique

  1. Assist superior rectus to raise cornea

  2. Assist inferior rectus to depress cornea
• Superior oblique muscle


  • Tendon passes through fibrocartilaginous pulley (trochlea) attached to frontal bone
  • Tendon turns backward and laterally
  • Inserted into sclera beneath superior rectus
• Muscles of the eyeball


  • Origins
  • Insertions
  • Nerve supply
  • Actions
• Clinical testing of eye movements


  1. Test superior/inferior recti by asking patient to look laterally

  2. Test superior/inferior obliques by asking patient to look medially and up/down

  3. Test lateral/medial recti by asking patient to look directly lateral/medial
• Cardinal positions of the eyes

  • Actions of recti and oblique muscles
• Intrinsic eye muscles


  • Ciliary muscle
  • Constrictor of iris
  • Dilator of iris
• Fascial sheath of the eyeball


  • Surrounds eyeball from optic nerve to corneoscleral junction
  • Separates eyeball from orbital fat
  • Provides socket for free movement
  • Perforated by tendons of orbital muscles
  • Reflected onto each tendon as a tubular sheath
  • Lower part thickened to form suspensory ligament of eye
• Coats of the eyeball


  • Fibrous coat
  • Vascular pigmented coat
  • Nervous coat
• Sclera


  • Opaque, composed of dense fibrous tissue
  • Fused with dural sheath of optic nerve
  • Pierced by ciliary arteries, nerves, and veins
  • Continuous with cornea at corneoscleral junction
• Cornea


  • Transparent, responsible for refracting light
  • Avascular and lacks lymphatic drainage
  • Nourished by diffusion from aqueous humor and capillaries at edge
  • Supplied by long ciliary nerves from trigeminal nerve
• Choroid


  • Outer pigmented layer
  • Inner highly vascular layer
• Components of ciliary body


  • Ciliary ring
  • Ciliary processes
  • Ciliary muscle
• Ciliary muscle


  • Composed of meridianal and circular smooth muscle fibers
  • Supplied by parasympathetic fibers from oculomotor nerve
  • Contraction pulls ciliary body forward, relieving tension in lens suspensory ligament, allowing lens to become more convex and increase refractive power
• Iris


  • Thin, contractile, pigmented diaphragm with central aperture (pupil)
  • Suspended in aqueous humor between cornea and lens
  • Muscle fibers are circular (sphincter pupillae) and radial (dilator pupillae)
  • Sphincter pupillae supplied by parasympathetic fibers, dilator pupillae supplied by sympathetic fibers
  • Sphincter constricts pupil in bright light and during accommodation, dilator dilates pupil
• Aqueous humor


  Clear fluid that fills the anterior and posterior chambers of the eyeball
• Aqueous humor flow


  1. Secreted from ciliary processes

  2. Enters posterior chamber

  3. Flows into anterior chamber through pupil

  4. Drained away through iridocorneal angle into canal of Schlemm
• Glaucoma


  Obstruction to draining of aqueous humor resulting in rise in intraocular pressure
• Functions of aqueous humor


  • Supports wall of eyeball by exerting internal pressure
  • Nourishes cornea and lens
  • Removes products of metabolism
• Vitreous body


  Transparent gel that fills eyeball behind the lens
• Functions of vitreous body


  • Contributes slightly to magnifying power of eye
  • Supports posterior surface of lens
  • Assists in holding neural part of retina against pigmented part
• Lens


  Transparent, biconvex structure enclosed in transparent capsule, situated behind iris and in front of vitreous body
• Lens structure


  • Elastic capsule
  • Cuboidal epithelium on anterior surface
  • Lens fibers formed from cuboidal epithelium at equator
• Suspensory ligament


  Attaches equatorial region of lens to ciliary processes of ciliary body
• Accommodation of eye


  1. Ciliary muscle contracts

  2. Pulls ciliary body forward and inward

  3. Relaxes radiating fibers of suspensory ligament

  4. Allows elastic lens to become more globular
• Presbyopia


  Reduced ability to accommodate due to lens becoming denser and less elastic with age
• Pupil constriction during accommodation

  1. Sphincter pupillae muscle contracts

  2. Pupil becomes smaller
• Convergence of eyes during accommodation

  1. Medial rectus muscles contract

  2. Eyes converge so single object is seen
• Eye trauma


  • Eyeball least protected from lateral side
  • Blowout fractures of orbital floor can cause displacement of eyeball, double vision, and loss of sensation
• Concomitant strabismus


  Nonparalytic strabismus caused by imbalance in opposing muscle action
• Direct light reflex


  1. Light shone into eye

  2. Impulses travel optic nerve to optic chiasma

  3. Impulses travel optic tract to oculomotor nuclei

  4. Parasympathetic fibers in oculomotor nerve reach ciliary ganglion

  5. Postganglionic fibers reach constrictor pupillae muscles
• Consensual light reflex


  1. Light shone into one eye

  2. Pupil of opposite eye contracts
• Accommodation reflex


  1. Focus shifts from distant to near object

  2. Impulses travel optic nerve, optic chiasma, optic tract, lateral geniculate body, optic radiation, visual cortex

  3. Visual cortex connected to eye field of frontal cortex

  4. Efferent impulses reach constrictor pupillae via oculomotor nerve, ciliary ganglion, short ciliary nerves