Cataract: Definition And Classification

Definition
The crystalline lens is a transparent structure. Its
transparency may be disturbed due to degenerative
process leading to opacification of lens fibres.
Development of an opacity in the lens is known as
cataract.
Classification
A. Etiological classification
I. Congenital and developmental cataract
II. Acquired cataract
1. Senile cataract
2. Traumatic cataract (see page 405)
3. Complicated cataract
4. Metabolic cataract
5. Electric cataract
6. Radiational cataract
7. Toxic cataract e.g.,
i Corticosteroid-induced cataract
ii. Miotics-induced cataract
iii. Copper (in chalcosis) and iron (in siderosis)
induced cataract.
8. Cataract associated with skin diseases
(Dermatogenic cataract).
9. Cataract associated with osseous diseases.
10. Cataract with miscellaneous syndromes e.g.,
i. Dystrophica myotonica
ii. Down's syndrome.
iii. Lowe's syndrome
iv. Treacher - Collin's syndrome
B. Morphological classification (Fig. 8.4)
1. Capsular cataract. It involves the capsule and
may be:
i. Anterior capsular cataract
ii. Posterior capsular cataract
2. Subcapsular cataract. It involves the
superficial part of the cortex (just below the
capsule) and includes:
i. Anterior subcapsular cataract
ii. Posterior subcapsular cataract
3. Cortical cataract. It involves the major part
of the cortex.
4. Supranuclear cataract. It involves only the
deeper parts of cortex (just outside the nucleus).
5. Nuclear cataract. It involves the nucleus of the
crystalline lens.
6. Polar cataract. It involves the capsule and
superficial part of the cortex in the polar region
only and may be:
i. Anterior polar cataract
ii. Posterior polar cataract