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Questions Answered: 300

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229
71

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Ophthalmology

Question 292 of 300

A 48 year old man presents to the Emergency Department with a new onset of diplopia. He has a past history of lung cancer with cerebral metastases. On examination you note that whilst looking straight ahead his left eye is abducted and depressed. There is ptosis of the left eye. The left pupil is fixed and dilated. Which structure is most likely compressed?

Answer:

The patient has features of oculomotor palsy.
  • Ptosis due to paralysis of the levator palpebrae.
  • "Down and out" position of the eye at rest is due to paralysis of the superior, inferior and medial rectus, and the inferior oblique. These muscles are innervated by the oculomotor nerve. There is unopposed activity of the lateral rectus and superior oblique causing the "down and out" position.
  • Dilated pupil due to unopposed action of the dilator pupillae muscle.

Cranial Nerve Palsy

Neurology / Ophthalmology

Last Updated: 18th August 2022

Cranial nerve II: Optic nerve

Cranial Nerve Optic Nerve (CN II)
Key anatomy
  • Formed from convergence of axons of neurons in ganglion layer of retina, surrounded by cranial meninges
  • Enters skull via optic canal of sphenoid bone
  • Receives blood supply from combination of anterior cerebral, ophthalmic and central retinal arteries
Function
  • Sensory: vision
  • Reflexes: afferent pathway of pupillary light reflex, afferent pathway of accomodation reflex
Assessment
  • Visual acuity (Snellen chart)
  • Colour vision (Ishihara plates)
  • Pupillary light response
  • Accomodation reflex
  • Optic disc (fundoscopy)
  • Visual fields
Clinical effects of injury
  • Ipsilateral monocular visual loss
  • Loss of colour vision
  • Abnormal pupillary light reflex
  • Visual field defect if damage to visual pathway
Causes of injury
  • Optic neuritis in multiple sclerosis
  • Optic nerve compression in orbital cellulitis, glaucoma, tumours
  • Optic nerve toxicity secondary to poisoning e.g. alcohols
  • Trauma e.g. orbital fracture, penetrating injury to eye
  • Ischaemia secondary to vascular disease

Cranial nerve III: Oculomotor nerve

Cranial Nerve Oculomotor Nerve (CN III)
Key anatomy
  • Arises from midbrain and passes through lateral aspect of cavernous sinus
  • Exits skull through superior orbital fissure
Function
  • Motor: innervates four extraocular muscles (inferior oblique, superior, inferior and medial rectus muscles), levator palpebrae superioris muscle (elevation of upper eyelid), sphincter pupillae muscle (pupillary constriction), ciliary muscle (accommodation)
  • Reflexes: efferent pathway of pupillary light reflex, efferent pathway of accomodation reflex
Assessment
  • Eye movements
  • Accommodation reflex
  • Pupillary light response
Clinical effects of injury
  • Depressed and abducted (down and out) eye at rest
  • Diplopia
  • Ptosis
  • Fixed and dilated pupil with loss of accommodation and abnormal pupillary light reflex
Causes of injury
  • Tumours
  • Aneurysms (carotid or posterior communicating)
  • Subdural or epidural haematoma
  • Trauma
  • Cavernous sinus disease
  • Diabetes mellitus

Cranial nerve IV: Trochlear nerve

Cranial Nerve Trochlear Nerve (CN IV)
Key anatomy
  • Arises from midbrain and travels through lateral aspect of cavernous sinus
  • Exits skull through superior orbital fissure
Function
  • Motor: superior oblique muscle of eye (intorsion, depression and abduction of eye)
Assessment
  • Eye movements
Clinical effects of injury
  • Weakness of downward gaze (difficulty reading/walking downstairs)
  • Vertical diplopia
  • Eye is extorted and may be elevated (patient head tilts to opposite side to compensate)
Causes of injury
  • Idiopathic
  • Trauma
  • Microvasculopathy
  • Cavernous sinus disease
  • Raised intracranial pressure

Cranial nerve VI: Abducens nerve

Cranial Nerve Abducens nerve (CN VI)
Key anatomy
  • Arises from pons and travels through cavernous sinus
  • Exits skull through superior orbital fissure
Function
  • Motor: lateral rectus muscle of eye (abducts eye)
Assessment
  • Eye movements
Clinical effects of injury
  • Convergent squint at rest (eye turned inwards) with inability to abduct eye
  • Horizontal diplopia
Causes of injury
  • Idiopathic
  • Brain tumours
  • Extradural haematoma
  • Cavernous sinus disease
  • Diabetes mellitus
  • Wernicke-Korsakoff syndrome
  • Trauma

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  • Biochemistry
  • Blood Gases
  • Haematology
Biochemistry Normal Value
Sodium 135 – 145 mmol/l
Potassium 3.0 – 4.5 mmol/l
Urea 2.5 – 7.5 mmol/l
Glucose 3.5 – 5.0 mmol/l
Creatinine 35 – 135 μmol/l
Alanine Aminotransferase (ALT) 5 – 35 U/l
Gamma-glutamyl Transferase (GGT) < 65 U/l
Alkaline Phosphatase (ALP) 30 – 135 U/l
Aspartate Aminotransferase (AST) < 40 U/l
Total Protein 60 – 80 g/l
Albumin 35 – 50 g/l
Globulin 2.4 – 3.5 g/dl
Amylase < 70 U/l
Total Bilirubin 3 – 17 μmol/l
Calcium 2.1 – 2.5 mmol/l
Chloride 95 – 105 mmol/l
Phosphate 0.8 – 1.4 mmol/l
Haematology Normal Value
Haemoglobin 11.5 – 16.6 g/dl
White Blood Cells 4.0 – 11.0 x 109/l
Platelets 150 – 450 x 109/l
MCV 80 – 96 fl
MCHC 32 – 36 g/dl
Neutrophils 2.0 – 7.5 x 109/l
Lymphocytes 1.5 – 4.0 x 109/l
Monocytes 0.3 – 1.0 x 109/l
Eosinophils 0.1 – 0.5 x 109/l
Basophils < 0.2 x 109/l
Reticulocytes < 2%
Haematocrit 0.35 – 0.49
Red Cell Distribution Width 11 – 15%
Blood Gases Normal Value
pH 7.35 – 7.45
pO2 11 – 14 kPa
pCO2 4.5 – 6.0 kPa
Base Excess -2 – +2 mmol/l
Bicarbonate 24 – 30 mmol/l
Lactate < 2 mmol/l
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