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cataracts

cataracts

introduction

  • cataracts occur when the proteins in the lens of the eye undergo changes resulting in opacification of the lens and are the leading cause of blindness in Western cultures
  • crystallins are the major soluble structural proteins in the lens and in humans comprise 3 major classes encoded by multiple genes: the α-, β-, and γ-crystallins.
  • as the β and γ crystallins denature, they precipitate and then form complexes with α crystallins which initially help to keep them soluble but eventually may become overwhelmed with the size of the complexes resulting in opacity
  • congenital cataracts can lead to permanent blindness by interfering with the sharp focus of light on the retina and resulting in failure to establish appropriate visual cortical synaptic connections with the retina.
    • prompt diagnosis and treatment can prevent this, although not all affect vision
  • cataracts can be grouped by anatomic location:
    • nuclear cataracts involve the centre of the lens and tends to initially cause some short-sightedness or improve reading vision but later clouds vision
    • cortical cataracts involve the periphery of the lens and usually cause issues with glare
    • posterior subcapsular cataracts involve the posterior part of the lens and thus often affects reading vision, vision in bright light, as well as causing halos around lights at night

aetiology

congenital cataracts

  • affect 1 to 6 children per 10,000 live births in industrialised countries and up to 3 times that in poorer countries
  • hereditary cataracts are estimated to account for 8%-25% of congenital cataracts and perhaps up to 50% 1)
  • aetiology:
    • “isolated”
      • tend to be highly penetrant mendelian traits, and usually AD
    • in association with metabolic disease or syndromes
      • galactosaemia
      • myotonic dystrophy
      • congenital rubella syndrome
      • Down's syndrome
      • Wilson's disease
      • perinatal-postnatal problems, such as hyperglycaemia and hypocalcaemia

early onset or pre-senile cataracts

  • commence before age 45yrs
  • aetiology:
    • trauma to the eye
    • uveitis
    • damage from intense light or x-rays eg. lasers, CT scans of face, radiotherapy to face
    • prolonged use of corticosteroids
    • metabolic diseases
      • galactosaemia

senile cataracts

  • these generally form some time after age 45 yrs
  • factors increasing risk:
    • genetics
      • individuals with an affected sibling have a 3-fold increased risk of having a cataract
      • heritability appears to account for around 50% of the liability for cataract
    • cigarette smoking
    • chronic exposure to environmental wood smoke
    • obesity or elevated blood glucose levels
    • poor infantile growth
    • exposure to UV light
    • alcohol consumption
cataracts.txt · Last modified: 2015/04/03 00:31 (external edit)