See an Ophthalmologist (Eye Doctor) to make sure you don’t have any diseases of the eye. Most if caught early can be controlled with eye drops or medication.

In the UK, eye testing is done by trained optometrists. They perform eye examinations and vision tests and can detect eye abnormalities and eye diseases. They are not medical doctors and will refer cases to ophthalmologists where necessary.

I would start with an optometrist who, as @flutherother says, can refer you to an ophthalmologist if need be. I wouldn’t go to one of the cheap eye glass chains though.

It depends upon the chart.

Optometrist should be sufficient.

Make sure they test you for glaucoma and get dilated. Bring very dark sunglasses. If you don’t have dark glasses make sure they give you dark glasses to wear home.