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Occulomotor nerve and Trochlear nerve

Examination of the optic nerve

Visual acuity
  1. By a Snellen’s chart held at 6m from the patient (if space is limited at 3m with a mirror)
  2. Acuity greater than 6/60 is dependent on the macular vision
  3. Each eye is tested separately
  4. If the patient cannot see the largest (Designated 60), reduce the test distance
  5. If at 1m ‘60’ letter cannot be read, use:

    1. Counting fingers held up at 1m
    2. Hand movements
    3. Perception of light

  6. If a patient cannot read 6/6 check the vision again using a pinhole occluder (Only the central light pass to the retina) – Can differentiate patients with poor vision due to:

    1. Refractory errors (Myopic – Short sighted, Hypermetrophia – Long sighted, Astigmatism – Cornea is not uniformly curved & light is not evenly focused on the retina)
    2. Ocular or neurological conditions 

Visual field
  1. Moving finger test

    1. The finger should be kept more than midway between you & the patient
    2. Patient closes one eye & fixes the gaze on your eye       

  2. Red pin confrontation test

    1. Use a red hatpin (d = 0.5cm) held at equidistance between you & the patient
    2. Use exactly same conditions above
    3. Check whether the patient & you see the pin at the same time                

  3. Binocular testing
Color vision
  1. Acquired defects

    1. Red color vision can be affected in optic nerve disease & macular disease
    2. Use a red target & check the difference of vision in both eyes separately

  2. Congenital defects          : Use a Ischihara color vision test 
Funduscopy Use check:
  1. Papilloedema
  2. Optic atrophy
  3. Pigmentary retinal degeneration
  4. Vascular diseases

3) Occulomotor nerve

  • It has 2 motor nuclei (At superior colliculus)

    1. The main motor nuclei
    2. The accessory parasympathetic nucleus (Edinger Westphal nucleus)

  • The main motor nucleus supplies extra ocular muscles

    1. Superior, Inferior & Medial recti
    2. Inferior oblique

  • The EW nucleus supplies via Ciliary ganglion & short Ciliary nerves to:

    1. Constrictor pupillae
    2. Ciliary muscles

  • Functions of the III nerve

    1. Lifting upper eyelid
    2. Turing the eye upward, downward & medially
    3. Constricting the pupil
    4. Accommodating the eye

4) Trochlear nerve

  • Most slender cranial nerve
  • Trochlear nerve nucleus locate At inferior colliculus
  • Only nerve to leave the posterior surface of the brain stem, emerge from the midbrain & immediately decussate with the nerve from the opposite side
  • Supplies the superior oblique muscle
  • Function is to turn the eye ball downward & laterally
Occulomotor nerve and Trochlear nerve Occulomotor nerve and Trochlear nerve Reviewed by Radiology Madeeasy on August 08, 2010 Rating: 5
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