The high osmotic pressure in a lens fiber as a driving force for the development of senile cortical cataract

In lens cataract, the clouding change in the lens leads to a decline of transparency of a part of the lens. There are three types of senile cataract: cortical cataract, nuclear cataract, and posterior/anterior sub-capsular cataract. The cataract that develops in most old people is cortical cataract. The clouding change in senile cortical cataract begins from the edge of the lens and develops progressively to lens centre. The pathology of a clouding change in cortical cataract is characterized by disruption of some lens fibers, swelling of some other fibers, and deposition of water between fibers. Based on the property of a lens fiber, we propose here a hypothesis on the mechanism of development of senile cortical cataract. I. Cortical cataract is triggered by the disruption of a cortical lens fiber as a result of an injury. The disrupted fiber will release water and crystallin proteins. II. The neighbor fibers can absorb this water due to the high intracellular osmotic pressure (IOP) and become swollen. Swelling makes a fiber be stiff and have increased risk to disrupt when it is curved during the accommodations of the lens. These fibers will release water again when they disrupt, and the water will make more local fibers swelling. In this way, the local fibers become swollen and then disrupt successively. III. The successive swellings and disruptions of local fibers result in the enlargement of a clouding change in lens. Since the fibers on the outer part of lens cortex have higher risk to be injured than that in the inner part, a clouding change starts from the edge of the lens. Conclusion: in our view, the progressive development of senile cortical cataract is a result of successive swellings and disruptions of local lens fibers, which is driven by the high IOP in lens fibers.