We discussed the crystalline lens extensively in a previous blog. It is important to discuss how cataract is developed in this avascular structure.
As I said earlier, Cataract is a clouding of the crystalline lens with a resultant reduction in subjective visual output! This clouding phenomenon undermines the transparent mechanism of the crystalline lens. Such factors ensure lens transparency and they include a) Avascularity of the lens materials, b) Tightly packed lens cell fibres, 3) The structural arrengements of lens cell proteins, 4) Semi-permeable nature of the lens cell capsule, 5) Active transport mechanism of the lens cell fibres, 5)Auto-oxidation and high concentration of reduced gluthatione in lens cells and, 6) coluration of the crystalline lens including other factors.
To fully understand pathogenesis of cataract formation, it becomes important to shed light on some factors that disrupts lens transparency.
For instance the primary reson the crystalline lens is avascular is to enable the structure transmit light without shadows or haloes that vascularity of structures often promote. Again, it is histologically documented that lens cell fibres are arrenged in a lattice three-dimensional way to reduce any interferance with light refraction though this medium. Also it should be noted that the tightly packed lens cell fibres especially as we approach the lens nucleus is apparently meant to reduce hydration of the lens cell fibres. Any disruption in this state of homeostasis triggers an apparent denaturing of lens protein, consequent upon which lens clouding ensues. What could disrupt this homeostasis relationship? Injury could. Aging is another factor. Let us not forget diseases like Diabetes, also the effect of radiation like the infra-red ray wich is absorbed in the crystalline lens (this is a protective function of the crystalline lens which in turn filters the kind of light reaching the very sensitive retina!) etc.
Metabolism of the lens fibre uses osmotic differentials to keep hydration in check, while using active transport to maintain sodium, potassium and calcium levels in the crystalline lens. Gluthatione, in its reduced form. Active transport mechanism helps allow selected materials into the crystalline lens and push out others into the surrounding areas while maintaining a threshood 'tension' that regulates dehydration of the lens fibre cells. Diseases, trauma, age and genetic disruptions have reportedly altered the metabolic activities of the crystalline lens hence the formation of cataract.
It should be noted that as the lens grow old it does not shed its old materials, it rather pushes them to the middle and associated wear and tear phenomenon of the lens makes the lens change from transparent to a graying shift. The later, including disruption in protein synthesis with age in some persons, is generally responsible for geriatric kind of cataract!
Commonly among the children is congenitial or genetic-induced cataract. Diseases among the parents prior to delivery could cause this. It could also be a result of food habit amongs the pregnant women. Exposure harmful rays in pregnant women or the use of drugs among these group has been implicated in the formation of congenital cataract!
There are about 17 million persons living with cataract all over the world and 75% are in Asia and Africa!
The most common type of cataract is geriatric cataract. Other types of cataract are not uncommon. In the youths and children the most common cause of cataract is genetic disruptions and trauma. Among a large swath of outdoor workers, radiation cataract is very common either through synthetic toxic materials or as a result of unhindered absorption of infra-red rich light common in hot regions.
Thanks... To be continued!
A catactous eye as seen under biomicroscope view courtesy of Karl
Dr Okwudiri Ezebuiroh.
This blog does not draw any financial interest anywhere. Thanks.
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