The vestibular system: structure and function.

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•The inner ear consists of a bony capsule known as the ‘otic capsule’ within the petrous portion of temporal bone. Anteriorly there is the snail like cochlear, in the middle there is the vestibule and posteriorly the three semicircular canals.

 

•The otic capsule is filled with fluid known as perilymph and suspended in the perilymph is a membranous labyrinth. These are delicate arrangements of sacs and tubes filled with a different fluid known as endolymph.

 

•The three membranous semicircular canals which occupy the corresponding bony structures are known as the anterior, posterior and horizontal semicircular canals. They are set at right angles and each represent a plane in space.

 

•The anterior end of each canal is dilated to form its ampulla. This contains a patch of neuroepithelium called the crista. The hairs of the crista are displaced following angular acceleration in that plane which triggers signal transduction along the vestibular nerve. 

 

•The canals come together at the vestibule which contains two further  significant regions; the utricle and the saccule. These contain a patch of neuroepithelium known as the macula. The macula contain calcium carbonate particles called  otoliths  and these are used to detect gravitational pull  (utricle) and linear acceleration (saccule).

 

•Nerves from the ampulla, utricle and saccule unite to form the vestibular nerve, the ganglion of which lies in the internal auditory meatus.

 

•Vestibular fibres from cranial nerve VIII terminate  in the vestibular nucleus in the medulla oblongata.  Axons then run to numerous areas of the CNS such as the spinal cord, the cerebellum, the cerebral cortex and the nuclei controlling extrinsic eye muscles. Fibres also communicate with the cerebellum to fine tune movement.

 

The acute red eye



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Acute angle closure glaucoma: Characterised by sudden onset painful red eye with vomiting from pain, halos seen around lights, decreased visual acuity due to corneal oedema, semi dilated  non reactive pupil and stony hard eyeball. There may be a history of intermittent subacute attacks. THIS IS AN OCULAR EMERGENCY which requires immediate treatment (iv acetazolamide, topical treatment and laser iridotomy).

Keratitis: This is inflammation of the cornea. Can be viral, fungal, bacterial or due to acanthoemeba (as seen in contact lens wearers). Presentation: unilateral photophobia, blurring, pain, eyelid oedema, discharge, hypopyon, dendritic ulcer (HSV) and stromal precipitates.

Conjunctivitis: This is inflammation of the conjunctiva. It can be bacterial, viral, chlamydial or allergic.

  Simple bacterial conjunctivitis:  subacute onset, bilateral, burning + discharge.  Gonococcal conjunctivitis presents with creamy discharge and oedema.

  Adenovirus: Types 8 and 19 cause contagious viral conjunctivitis. (types 3, 4 and 7 associated with pharyngitis). Acute onset, bilateral, watering, redness, discomfort and photophobia.

  Adult chlamydial conjunctivitis presents with chronic unilateral discharge. Neonatal forms may pass from mother to child. Trochoma occurs in developing world where chlamydia trochomatis is carried by the common fly à associated with scarring.

  Vernal (allergic) conjunctivitis: associated with atopy. Causes burning, photophobia, itching and characteristic cobblestone papillae.

Uveitis: This is inflammation of the uvea (iris, ciliary body and choroid together).  Can manifest as anterior uveitis (predominantly iritis), intermediate uveitis, posterior uveitis or panuveitis.  May be acute or chronic.  Presentation of acute uveitis:  unilateral, pain, photophobia, injections around the limbus, no itching, poorly reactive pupil. Signs: keratic precipitates (KPs), posterior synechiae and hypopyon. This is associated with HLA-B27 and AS.

Other things to look out for in the acute red eye include a hx of trauma, foreign bodies and operations (eg. post op endophthalmitis).

Complications of treatment for hyperthyroidism

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1.Anti-thyroid drugs: Carbimazole and propylthiouracil. Main side effects are neutropenia but rashes are also common.

 

2.Radioactive iodine: Insufficient dosing may lead to recurrent thyrotoxicosis.  Patient may eventually develop hypothyroidism.  There is a theoretical risk of malignancy associated with radioactive iodine so it is reserved for older patients. Pregnancy is an absolute contraindication.

 

3.Surgery: usually a subtotal thyroidectomy. Complications are those associated with any surgical procedure but also: damage to recurrent laryngeal nerve leading to vocal cord paralysis, haemorrhage causing tracheal obstruction, hypocalcaemia due to parathyroid damage, thyrotoxic crisis due to release of thyroid hormone during surgery.

Symptoms and causes of hypoglycaemia



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Symptoms:

Adrenergic overactivity (sympathetic symptoms):

•Palpitations

•Pallor

•Sweating

•Nausea

•Tremor

•Anxiety

•Dilated pupils

Neurological symptoms (insufficient glucose in CNS)

•Confusion

•Difficulty in concentrating

•Slurred speech

•Personality change

•Double vision

•Seizures

•Hunger

•Coma

Causes:

Increased activity / reduced food intake / increased insulin administration / concomitant alcohol administration / excess dose of sulphonylureas especially longer acting ones such as chlorpropamide or glibenclamide when used in the elderly.