Here is the procedure:

1. Go to Medical Commission office with the following documents

a. Original passport
b. Visa extension form duly filled-up
c. Copy of the visit visa

and don't forget to carry Credit/Debit/other card to pay the fee. It is QR 100, but no cash payment.

2. No need to carry photographs - it will be taken

3. Check the results here:

http://www.sch.gov.qa/mcr/En/mcresults.jsp

4. Go to immigration office with original passport, and visit visa extension form duly filled-up for the extension after appx 3 days. Extension may be allowed for one month or more.Again, no cash payment.