Mulberry, I think the reason why bobbio had said you're not going to earn a dime from shadowing is because "job" implies getting paid/earning money. Shadowing/interning/volunteering, on the other hand, implies being unpaid to gain experience.
It's more important to shadow an optometrist and actually sit in the exam room to observe him/her. You'll be able to see what types of patients are normally seen, how optometrists handle children, elderly, non-English speaking patients, or other more challenging patients. During shadowing, you'll also be able to see patients with rare conditions and observe how the optometrists problem solve. You'll also be able to see what a typical day would be like.
If you had a paid, optometry-related job, you could only be an optometry assistant, optician, or receptionist and you won't be in the exam room all day observing. You'll be handling paperwork, scheduling phone calls, helping patients with frame selection, checking in frames/contacts and other clerical work. Although it is paid, and you'd see another aspect of an optometric office, it will not give you a real sense of what the job of an optometrist entails. Remember, your ultimate goal is NOT to be an optician, optometry assistant, etc. and an optometry-related job is training how to work in those particular positions. These jobs will benefit your application, but not as much as shadowing.
Qualities you could potentially get out of optician/assist/reception jobs are people skills, communication skills, organization, patience, etc. but if you can't land an optometry-related job, you could learn these skills doing human resources, waitering, tutoring or any job that requires you to work with a diverse group of people and you could definately work these traits into your application and experience.