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Eye

Anatomy & Physiology

Structure

Function

Clinical Conditions

Cataract

Opaque proteins within the lens leads to loss of lens elasticity. These build up in conditions such as rubella, Down’s syndrome, senile degeration, diabetes mellitus and corticosteroid therapy. Removal of the lens and replacement with a synthetic plastic one does the trick.

Glaucoma

Normal intra-ocular pressure is 15-20mmHg. If there is an increase in production of aqueous fluid, or a blockage to its outflow, or a space occupying lesion, then this pressure will rise. It impedes bloodflow to the retina, resulting in blindness.

Inflammatory lesions

  • Chlamydia can cause trachoma – which can cause blindness
  • Bacterial infections can cause glaucoma (see above)
  • Viral infection from herpes simplex can cause problems.
  • There are rare parasitic infections too.

Retinal Ischaemia

Usually due to the blocking of a blood vessel from atheroma, etc. It causes death or damage to photoreceptive cells in the retina. Most commonly happens in diabetics or hypertensives. Can be seen as yellow retinal lesions in an ophthalmoscope, as can dot and blot haemorrhages. Can lead to neovascularisation, where new vessels form around the lesion – which blocks the photoreceptor cells and leads to a loss of vision.

Optic Neuritis

Sudden onset of (usually) one sided blurring of vision. Rarely complete loss of sight, and also rarely in both eyes. It occurs due to inflammation of the optic nerve, which swells up the myelin sheaths, sometimes killing them off. Usually returns to normal in a couple of weeks. Most common in Multiple Sclerosis, where it is often the presenting complaint, but also caused by infections or by auto-immune conditions.

Tumours

A large variety of tumours can form in the eye, although generally, if a primary, recovery rates are fairly good on removal of the eye.