The specific standards will depend on your country's regulations.
Here are the first class medical requirements in the US:
You can read more here:
Medical Requirements in the UK:
To get your atp certificate, you will need to pass an faa class I medical examination. In this examination you will have your eyes checked(i think the standard in 20/20 un OR corrected, both) hearing(conversational volume), and fill out a form with extensive information on your medical history. You can also expect a blood pressure check and an EKG. The one thing you need to remember is to be honest with the docter.(This is mainly because i see planes flying over my house everyday and i really don't want the pilot to have a heartattak and crash in my neighborhood.) I was with my asthma and still got my class two med, no waviers.
Yes you should ensure that you are fit before get on to become a pilot.
Check this resource on all medical requirements for a Commercial pilot