Cataract is 30 percent more common in diabetic than in non-diabetic persons. Cataract development is a physiologic manifestation of ageing, but this process occurs earlier and more quickly in diabetic people. The mechanisms of cataract development in ageing and in diabetes are similar. The polyol pathway has been incriminated in cataract production in experimental models of diabetic animals, with resultant accumulation of sorbitol and galctitol (a product of galactose) in the lens. This view is strengthened by the beneficial effect that aldose reductase inhibitors have on inhibition of this process and cataract formation, on condition these medicines are used early in diabetic patients. Furthermore, the role of lack of myoinositol or special aminoacids has been discussed, as well as the detrimental effect of free radicals, a view supported by the beneficial effect of antioxidant substances on delay or even prevention of cataract formation. The current prevailing view, however, for the mechanism of cataract formation is the enzymatic glycosylation of the lens contents and especially of the crystalline protein fibres. This process evolves at an accelerating pace in diabetes. At the same time the glycosylated crystalline fibres are more susceptible to oxidative damage, a process that is accelerated by their bipolar interaction with disulphide bonds. This leads to formation of molecular entities of higher molecular weight, resulting in the loss of the ability to diffuse light inside the lens. Similar phenomena have been observed with ageing.
It is also interesting that the enzymatic glycosylation theory can be connected to that of polyol formation, since it was proven that aldose reductase inhibitors inhibit not only the protein glycosylation but also the formation of pentosidine bonds, which is considered an index of long-term protein destruction.
Cataract removal can deteriorate existent maculopathy and proliferative DR if intraoperative complications occur. For this reason, cataract operation is decided only when the quality of the patient's life has been seriously affected from loss of vision or when the ability to detect and treat underlying DR is being hampered by the presence of the cataract lens. Disk oedema and proliferative DR should be treated with laser photocoagulation before the surgery, if possible. The process of the operation includes destruction of the cataract lens with the use of ultrasound (photocoemulsification), whereas the effect on vision can be worse than in non-diabetic subjects, due to possible deterioration of coexistent retinopathy and especially maculopathy. Finally, the possibility of postoperative inflammation is higher in diabetic people. The use of acrylic or heparin-eluted lenses is indicated, since they cause fewer inflammations or cellular deposits compared to silicone lenses. Silicone can be used during vitrectomy.
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