The causes of macular edema are numerous and different causes may be inter-related. It is commonly associated with diabetes. Chronic or uncontrolled diabetes type 2 can affect peripheral blood vessels including those of the retina which may leak fluid, blood and occasionally fats into the retina causing it to swell.
Visual C++. Visual C++ is known as a native development language, as it talks directly to the hardware for the Windows Mobile device, with no intervening layers (unlike Visual C#, for example). Programming using C++ can be challenging, as it is not a trivial language to learn.
Assembly language primer. Most modern operating systems are written in C/C++. That's very useful when portability and code-maintainability are crucial, but it adds an extra layer of complexity to the proceedings. For your very first OS, you're better off sticking with assembly language, as used in MikeOS.