I heard that many ophthalmologists do some lid procedures where there is lots of blood. Some people also said that cataract surgery involves blood too. Though I am not very sure about this, I think they may need to deal with that because many doctors as well as nurse may need to deal with blood. If you can't deal with that, I suggest you to change your major.
Cataract surgery should not involve any blood. But during your school days, you may need to deal with blood. If you can get used to that, you can become a qualified ophthalmologists. There might be lots of blood involved there which can help you get used to that kind of situations.
You may need to deal with blood. My aunt is a nurse. A few years ago, I also wanted to be a doctor but not a doctor of optometry. I was afraid of blood. So my aunt asked me to change my major. Though some people could get used to that situation as time passed but it seemed that it was not a good major for those who were afraid of blood in the beginning. So later I changed my mind. Now I am far away from blood. I am happy that I haven't chosen that major.