Can LASIK reduce the probability of retinal detachment for a very nearsighted person?
As you obviously already know in asking this question, high myopia (nearsightedness) is associated with a higher overall risk of retina problems, one of the most serious being detachment. The reason for this is directly related to the cause of myopia: a larger globe (eyeball) than normal, meaning a further distance to the retina than the cornea/lens are built to focus. We don't really know why this happens in the developmental years, but genetics, inadequate exposure to natural light, and literacy are all implicated. As the eyeball grows, it stretches the retina which overlays the inside wall of the globe. If certain areas of the retina, particularly those in the periphery, get stretched enough to cause significant thinning, holes or tears are more likely to occur. These can be the cause and site of the beginning of a retinal detachment.
Contact lenses, ICLs, and LASIK all work by reducing the focusing power of the cornea, thereby moving the default focal point further back in the eye -ideally right onto the central retina. But none of these will change the size of the globe, nor do they "undo" the stretch on the retina. A LASIK eye with 20/20 vision is still a myopic, large diameter eye anatomically.