VSR 421: Regional Veterinary Surgery (2+1)

CLASSIFICATION

• Congenital cataract – Cataract present at birth. (Note: In foetal life the lens receives its nutrition through vascular channels. After birth the lens is entirely dependent on the aqueous humour for its nutrition. In puppies and kitten it is normal for the vascular covering of the foetal lens to persist for a few days after the eyes have opened. This should not be mistaken for congenital cataract.)
• Acquired cataract – cataract developing later in life
• Complete cataract, involving the lens completely.
• Partial cataract. 
• Progressive cataract.
• Stationary cataract.
• Juvenile cataract. -  Cataract seen in young animals.
• Senile cataract – Cataract developing due to old age. This is common in veterinary practice.
• Diabetic cataract – This also is not seen in veterinary practice. Diabetic cataract is characterized by minute opacities developing on the superficial cortex of the lens due to turgidity of cells in the superficial cortex of the lens. The turgidity of cells is apparently associated with the sugar content of aqueous humour.
• Toxic cataract – Cataract caused by the circulation of toxins or poisons in the body, e.g., cataract due to equine influenza, periodic ophthalmia, distemper, chronic nephritis, ergot poisoning in cattle and pigs, experimental feeding of naphthalene, etc.
• Capsular cataract – (Anterior capsular cataract and posterior capsular cataract). This is not common.
• Cortical cataract – (Anterior cortical and posterior cortical cataracts). Majority of cortical cataracts are stellate cataracts, i.e., spreading from the centre of the lens to its periphery. Cortical cataract sometimes develops as a complication of a perforating corneal ulcer.
• Pyramidal cataract – A localized opacity of the lens.
• Lamellar cataract – The opacity is seen in the area between the lens nucleus and cortex.
• Perinuclear cataract – This is lamellar cataract seen in horses.
• Nuclear cataract – Confined to the central portion (nucleus) of the lens.
• Diffuse cataract – Spreading evenly through the entire lens substance.
• Calcareous cataract – Cataract in which the lens substance is partly converted into chalky materials.
• Depending on the stage for surgical removal of the lens cataract is describes as:
• Immature, mature or hyper mature cataract.
• Immature (unripe) cataract is a cataract in which the lens has not become completely opaque.
• Mature (ripe) cataract is one in which the entire lens substance has become opaque and is indicated by a grey white or amber colour. This is the best stage for surgical removal of lens.  

  

  Mature cataract in a dog

• In hyper – mature cataract there may be partial calcification of the lens and some portion of the lens may also undergo liquefaction. The cortex appears milky white in colour. The nucleus of the lens may sink into the bottom of liquefied lens substance. Complete removal of the lens is difficult when the cataract is hyper – mature.