Registered Nurse:Nurses have to be licensed. They normally have schooling and get an associate degree in nursing(2-3 years of schooling), bachelors degree in nursing(4 years of schooling), or they go to an approved nursing school and get a diploma(2-3 years of schooling.
Optometrist:Before Optometrists go to an optometry school they must first have a bachelors degree at a postsecondary school (college or university) which takes about 3-4 years.
After they have completed this they go on and go to Doctor of Optometry school this school takes about 4 years to complete. After this some do one year of residency to get some experience in the field.
Doctor: To get into medical school can be very difficult. You have to do well on you MCAT (Medical College Admissions Test), you have to letters of recommendation, have good leadership qualities and a good personality, and participate in extracurricular activities, becasue these are all things that the medical schools want to see to determine wether to accept you to that medical school.
Before doctors can move on to medical school they have to have a bachelors degree, yet some have an advanced degree.