I was one of those investigators. Soft contact lenses should be not be used during the five to seven days prior. Hard contact lenses should not be used for approximately one month for each decade the patient has worn them. The majority of patients have both eyes done at the same time. I have lasered over 250 eye doctors and their families, and only one eye doctor has chosen to have one eye at a time treated.
Most patients choose to have both eyes treated at the same time for several reasons.
One is convenience. Some of my happiest patients are in their seventies. As long as the patient is a good candidate, there's no reason for age to be a limiting factor. The three major risk factors for laser surgery are large pupils, high astigmatism or irregularity of the corneal surface, and high degrees of nearsightedness or farsightedness. There are other risk factors as well, and the only way to determine if you are a good candidate is to have a thorough consultation with a reputable eye doctor.