I did this rotation as a 4th year and would STRONGLY recommend it to anyone that can accommodate it in his or her elective schedule. Dr. Eagle is a true gem of the ophthalmology world and you learn so much that will be useful to you as a beginning resident.
I'm not sure about opportunities for research. Perhaps if you're very proactive. There's definitely time though - during this rotation I was also finishing my med school thesis and applying to prelim year programs.
Also consider rotating with Dr. Dubovy at Bascom Palmer. He's an ocular pathologist/medical retina specialist and one of the best teacher I've ever had. Since he's in retina clinic a couple of days per week, you'd also have the opportunity to choose an attending to shadow or could rotate in our ER. You can learn a ton of exam skills and pathology here...