From the NASA website:
Basic requirements for an Astronaut Pilot include the following:
1. Bachelor's degree from an accredited institution in engineering, biological science, physical science, or mathematics. An advanced degree is desirable. Quality of academic preparation is important.
2. At least 1,000 hours pilot-in-command time in jet aircraft. Flight test experience is highly desirable.
3. Ability to pass a NASA space physical which is similar to a military or civilian flight physical and includes the following specific standards:
* Distant visual acuity: 20/100 or better uncorrected, correctable to 20/20 each eye.
* Blood pressure: 140/90 measured in a sitting position.
* Height between 62 and 75 inches.
Basic requirements for a Mission Specialist include the following:
1. Bachelor's degree from an accredited institution in engineering, biological science, physical science, or mathematics. Degree must be followed by at least three years of related, progressively responsible, professional experience. An advanced degree is desirable and may be substituted for part or all of the experience requirement (master's degree = 1 year of experience, doctoral degree = 3 years of experience). Quality of academic preparation is important.
2. Ability to pass a NASA space physical, which is similar to a military or civilian flight physical and includes the following specific standards:
* Distance visual acuity: 20/200 or better uncorrected, correctable to 20/20, each eye.
* Blood pressure: 140/90 measured in a sitting position.
3. Height between 58.5 and 76 inches.
Are waivers granted for any of the medical requirements?
No, NASA does not grant waivers for the medical requirements. When qualifying astronauts for space flight, NASA must look at not only what is required for normal Shuttle operations, but also what each astronaut would require should serious, even life threatening, problems develop. For maximum crew safety, each crewmember must be free of medical conditions that would either impair the person's ability to participate in, or be aggravated by, space flight, as determined by NASA physicians.
You probably need to contact them directly for your specific questions.