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Cataracts are the clouding of the normally clear lens of the eye. They can affect one or both eyes and can develop as a primary or secondary ocular design process. In chickens, cataracts can often occur as a result of certain viral diseases (such as avian encephalomyelitis or Marek's disease), genetics, increased age, exposure to continuous light, or from nutritional deficiencies (vitamin A or E). Since the lens in a healthy eye is clear like a camera lens, light has no problem passing through the lens to the back of the eye to the retina where images are processed. When a cataract is present, the light cannot get through the lens as easily and, as a result, chickens often become blind.


Cloudy eye(s)
Sensitivity to light


  • History
  • Clinical signs
  • Physical exam


Supportive care


Scientific References

Good Overviews

Risk Factors

  • History of avian encephalomyelitis.