Not sure how the other schools' programs are like, but I know Berkeley requires we rotate in several specialty clinics and work in primary care and eye wear 4-5 days/week during 3rd year. UC Berkeley's eye clinics are located on an urban college campus, so we see a wide range of patients, from the homeless to the deans to the typical college student to the elderly immigrants. We see lots of ocular diseases (especially glaucoma patients) and outside clinics often refer their patients to our clinic. We also see patients with rare vision conditions and special needs who moved to this area for its accommodating public transportation.
hopeful_opt is right, locations is a factor. Schools located in urban areas like UCB, SUNY and ICO probably see such a huge volume of patients that you're bound to come across some with ocular disease.