Measure eye thickness?

I went to the optometrist today and he said I have high eye pressure he said the normal is 17 and I am 22. He recommended me to go to an ophthalmologist to test the thickness of my eye. He said that if my eye is thick then the high pressure is normal. I am scared of two things: 1. how they are going to test the thickness if it hurts or not. 2. what could happen if I get high pressure.