Disturbance occurs before birth
Causes may be genetic, malnutrition, infectious disease during first trimester of pregnancy (like mumps, measles, chicken pox), birth trauma
Acquired cataract – opacification occurs due to degeneration of the already formed normal lens fibres.
l. Senile cataract- age related, characterized by an initial opacity in the lens, subsequent swelling of the lens and final shrinkage with complete loss of transparency
2. Traumatic cataract- due to penetrating or blunt injury or laceration and foreign bodies in the eye.
3. Complicated cataract- opacity of lens secondary to some other intraocular disease
4. Metabolic cataract- due to endocrine disorders and bio-chemical abnormalities
5. Radiation cataract- exposure to radiation
7.Dermatogenic cataract- associated with skin diseases
8.Toxic cataract- due to medications- corticosteroids, thiazides, tetracycline etc.
B. Morphological classification
l .Capsular cataract- involves the capsule and may be anterior capsule or posterior capsule
2.Sub capsular cataract- involves superficial part of the cortex and include anterior subcapsular or posterior subcapsular
3.Supranuclear cataract- involves only deeper parts of the cortex
4.Polar cataract- involves the capsule and superior part of the cortex in the polar region only
5.Cortical cataract- the lens fibres of the cortex are mainly affected
6.Nuclear cataract- involves nucleus of the crystalline lens
Reduction in oxygen uptake & an initial increase in water content followed by dehydration of the lens
Na & Ca contents are increased
K, ascorbic acid & protein Contents are decreased
The protein in the lens undergoes numerous age related changes
(Lens starts turning in to Yellow coloured & leads to formation of fluorescent compounds, molecular changes)
In addition to the above photo absorption of UV light
Opacity of the lens