A few programs offer a combined intern year with residency, and may integrate actual ophthalmology rotations that are useful. If you can find such a residency, consider yourself very lucky, because once you start as an official ophthalmology resident, you'll be ahead of the curve. My program had a combined internship/residency track where we had 4 months of neuro-ophth/general, one month as a virtually functional first year ophthalmologist, and a ocular pathology month. It definitely paid dividends when I started as an official ophthalmology resident.
Many programs, however, don't have such a deal and you're often on your own finding an internship/TY year. This has been discussed nearly ad nauseam on this forum, but for the most part, it's not necessary to find an internship that is clinically strong but brutal on your lifestyle. There are advantages of doing an intern/TY year at the program where you'll be at for residency that makes the transition easier, but everyone has their own unique insight into it.