I may not come over to the Mac side now. Long time PC user here wanting to switch but I need to be able to see what I'm doing. Aging eyes and I use my computer a lot for both work and play.
go into an apple store and try out a retina macbook pro (iMacs and displays will go retina soon).
Use it the way you would and see how it works for you. You can use the Command + key combination to enlarge text and Command - to go back. You can change the default text size in Safari and of course there are other browsers. You can even schedule an appointment with someone there to show how to address your concerns.
Service is amazing. Literally call up, ask for the manager, tell him you are considering a Mac and you have these concerns and could he assign the right employee to sit down with you and show you Accessibility features, and solutions in various apps you would be using, and they will happily do all that, one on one, and without any negative attitude.
He will know which of his employees would be good for that, and you can set a time. Which computer you get and how you use it is important and you should try this, don't give up on it. With Retina, you can make everything larger and it stays sharp. I'd wait until after Yosemite releases, though.
I turned off Transparency and turned on Increase Contrast in Accessibility and this helped my eyes a lot.