While you can get prescription swim goggles, cycling and running sunglasses and Rx podium shades, it is the transitions that make things challenging. Do you wear your Rx swimwear walking down to the water? When do you swap your goggles out for the Rx sunglasses? (don’t start riding with your goggles on)
The easiest solution for all these questions is probably to consider contact lenses. For triathlon, you will definitely want a daily disposable lens since you will be swimming in them. Even if you aren’t swimming in the sludgey waters of Rio, there are still a lot of bacteria in all bodies of water that you don’t want living in your contacts for an entire month. This solution allows you to use non-Rx goggles, alleviates the confusion in transition and allows for any sunglasses frame to be used for the bike and run. And yes, for those of you who need multifocal glasses to read your Garmin, there are multifocal daily disposable contact lenses.
For those too squeamish to put in contacts, there are still options on the table. Prescription goggles are available from some optometry offices and can make a world of difference. Even if you are just using them in the pool, it is nice to be able to see the clock. For open water swims, they are a near must, sighting is already tricky enough for those who can see, why swim all over the place wasting time?
Cycling is probably the most challenging element of triathlon when it comes to eyewear. It is imperative to have a high wrap frame to block wind and protect your eyes, but I have found that most sunglasses don’t give enough room in the top of the lens for looking ahead when in the aero position and I end up looking over the top of the frame.
There are a few ways to put a prescription in a pair of glasses for cycling. The best option is to choose a more "moderate" frame similar to the Wiley X Rebel (an awesome local company out of Pleasanton California).