To be off topic, in my experience, the "letter committee" at my school was next to useless for optometry. We have a very competitive med school so the writers only concentrate on med school. They don't even really know details about optometry school. They couldn't tell you what is an acceptable OAT score was.
To be on topic, I agree with mthwong. You should definitely prepare some kind of "package" or instructions. All schools want the LOR's to be written on OFFICIAL LETTER HEAD and in an official envelope signed and sealed so I personally did not include pre-addressed envelopes. Stamps I only gave to people like my employer or OD I shadowed and more personal references b/c school references/professors can just use department envelopes and stamps. That's exactly what the school wants them to use them for.
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Then, I made a list of the schools I was applying for and arranged them into columns. One column for the letters to be mailed directly to the school (w/ corresponding addresses included) and another column for letters to be signed and sealed with enclosed cover letter and sent to my house. Those ones are the ones that you have to send in an application package to the optometry school (ex. ICO and PCO)
The schools won't think you opened them b/c they will be "signed and sealed." So obviously dont open any letters that come back to your house signed on the back flap!!!
Also, I found it easier to cut and paste blurbs about what the schools wanted the writer to evaluate about me on the same sheet with the school addresses. This way the writers had some general direction in addition to some on-line forms. Then I told them to just write one letter and send the same one to all of the schools so they dont have to fill out separate forms for each school. I think schools like personal written letters over the pre-made forms. Then it seems like a more personal description of your character. Hope this helped.