Cataracts are generally described as being age-related (senile) or secondary. Age-related cataracts are the most common kind of cataract and are the result of the natural aging process. Despite their name, they can happen at any age, though they become more common as people get older.

Secondary cataracts are due to causes other than aging. These factors include diabetes. Cataracts can also result from:

• Medical treatments. These include:
  
• • Surgery for glaucoma or other eye conditions.
    
    
  • Vitrectomy, a procedure sometimes used to treat diabetic retinopathy.
    

    

  • Certain drugs, particularly long-term use corticosteroids. This class of anti-inflammatory immunosuppressives is also a risk factor for conditions including diabetes and glaucoma.
    
    
• Trauma. Cataracts resulting from eye injuries are known as traumatic cataracts. In some cases, it may take years for traumatic cataracts to occur.
  
  
• Radiation. Radiation cataracts are linked to exposure to radiation.
  
  
• Congenital conditions. Cataracts can be present at birth or form during childhood.

Cataracts can also be classified according to their location in the lens. These types include:

• Nuclear. These develop slowly in the center of the lens. In early stages they may cause nearsightedness. Patients may experience a temporary improvement in reading vision, “called second sight,” that ends as the cataract worsens. Nuclear cataracts may especially impair night vision and can significantly dull the appearance of color. Nuclear cataracts are the most common age-related cataract.
  
  
• Posterior subcapsular. These usually form in the back of the lens. Subcapsular cataracts may reduce reading vision, impair vision in bright light and create the perception of halos or glare around lights at night. They generally develop faster than nuclear cataracts.
  
  
• Cortical. These begin on the edge of the lens and can expand toward the center. Cortical cataracts may especially affect focusing, glare and perception of contrast.

Mixed opacity, sometimes used to refer to any combination of the above, is common.