axes of the eye

• Axes of the eye

  Imaginary line on how the light enters the eye. Used to pinpoint the exact location of abnormality/lesion and refer properly to ophthalmologist.
• Regional anatomy


  Per part of the body
• Optic axis / Y axis / Antero-postero axis / Sagittal axis

  Horizontal line from the vertex (peak-center-steepest area) of the cornea to the posterior pole of the retina. 24 mm in length (normal) - emmetropia (not considering the strength of optical media). Torsional movement (rotation) takes place with center rotation.
• Center rotation


  Central point with the distance of 13.5mm from the vertex (peak) of the cornea.
• Transverse axis


  Line passing through the center rotation of the eyeball and right angle (90 degrees) to optic axis. Responsible for vertical movement. 22mm in length (normal).
• Vertical axis / Z-axis / Supero-inferno axis


  Superior-inferior line passing through the center rotation. Responsible for horizontal movement. 22mm in length (normal).
• Planes of the eye

  • Horizontal plane
  • Median plane
  • Equitorial plane
• Horizontal plane


  Where optic axis and transverse axis lies. Divides the eye to upper and lower portions.
• Median plane


  Where optic axis and vertical axis lies. Divides the eye to right and left hemisphere.
• Equitorial plane


  Where transverse axis and vertical axis lies. Divides the eye into anterior and posterior portion.
• Mnemonics: HOT - horizontal plane wherein optic and transverse axis lie. MOV - median plane wherein optic and vertical axis lie. ETV - equitorial plane wherein transverse and vertical axis lie.
• Extra ocular muscle (EOM)

  • 4 Recti muscles: Superior rectus, Inferior rectus, Medial rectus, Lateral rectus
  • 2 Oblique muscles: Superior oblique, Inferior oblique

  
• Annulus of Zinn


  The point where all the EOM muscles originate from, except the inferior oblique muscle which originates in the inferior orbital rim.
• The average length of all the EOM was 40mm.
• Cranial nerve innervation of EOM

  All EOM are innervated by CN #3, except lateral rectus (CN#6) and superior oblique (CN #4).
• Spiral of Tillaux


  The point of connections of all recti muscles.
• Physiology of EOM

  • Tracking mechanism of the eye
  • Fixation
  • Binocular vision
  • Eye movement in different gaze
• Recti muscles


  Their primary actions are horizontal and vertical.
• Medial rectus

  Strongest, heaviest and broadest muscle. Can cause overaction, causing inward motion of the eye (deviation). Has the closest insertion to the limbus. Works only in horizontal plane of action.
• Lateral rectus


  Works only in horizontal plane of action. Innervated by CN #6. Abduction - movement of one eye outwards.
• Superior rectus

  Has the farthest insertion from the limbus. Longest muscle. Forms a 23 degree angle nasally. Innervated by CN #3. Helps with the rotation of the eye, when retracting either inwards or outwards.
• Inferior rectus


  Forms a 23 degree angle nasally. Innervated by CN #3.
• Oblique muscles


  Their primary action is torsional (rotation - tertiary movement).
• Superior oblique


  Longest muscle because of the tendon (trochlea) which acts as a pulley. Innervated by CN #4.
• Inferior oblique


  Innervated by CN #3. Originates from the inferior orbital rim / inferior nasal orbital rim.
• The distance of the insertion of the muscle from the limbus is important.
• Benzene ring

  Gross diagram that shows which muscle move when the eye moves to a given direction.
• Terminologies


  • Primary motion
  • Secondary motion
  • Tertiary motion
• Terminologies


  • Elevation
  • Depression
  • Abduction
  • Adduction
  • Agonist
  • Antagonist
  • Synergist
  • Yoke
  • Duction
  • Version
  • Vergence
• Movement of the EOM


  • Intorson
  • Extortion
• Movement of the eye

  • Duction: Adduction, Abduction, Supraduction, Infraduction, Excycloduction, Incycloduction
  • Version: Dextroversion, Levoversion, Supraversion, Infraversion, Dextroinfraversion, Dextrosupraversion, Levoinfraversion, Levosupraversion
  • Vergence: Convergence, Divergence, Positive vertical divergence, Negative vertical divergence, Incyclovergence, Excylovergence
• 9 position of gaze

  • Ortho
  • Dextroversion
  • Levoversion
  • Supraversion
  • Infraversion
  • Dextrosupraversion
  • Dextroinfraversion
  • Levosupraversion
  • Levoinfraversion
• Hearing's law of equal innervation states that when a nervous impulse sent to a muscle causing it to contract, an equal and opposite impulse is sent to the antagonist muscle to prevent excessive movement.
• T EYE TURNS UP; LEFT EYE TURNS DOWN

  Positive vertical divergence
• NEGATIVE VERTICAL DIVERGENCE


  RIGHT EYE TURNS DOWN; LEFT EYE TURNS UP
• INCYCLOVERGENCE / CONCLINATION / INTORSION

  VERTICAL MERIDIANS OF BOTH EYE ROTATES INWARD
• EXCYLOVERGENCE / DECLINATION / EXTORSION

  VERTICAL MERIDIANS OF BOTH EYE ROTATES OUTWARD
• 9 POSITION OF GAZE

  • ORTHO - equal (PRIMARY POSITION - both eyes are alight equally together)
  • DEXTROVERSION – both eyes to the right
  • LEVOVERSION - both eyes to the left
  • SUPRAVERSION - both eyes upwards
  • INFRAVERSION - both eyes downwards
  • DEXTROSUPRAVERSION - both eyes right and up
  • DEXTROINFRAVERSION - both eyes right and down
  • LEVOSUPRAVERSION – both eyes left and up
  • LEVOINFRAVERSION - both eyes left and down
• Mostly applied in neuro eye exam and binocular vision, diagnosing if there's paratic muscle
• Paratic muscle


  Paralyze muscle