Several opticians (I think Vision Express are one high street chain) are familiar with the eye examination required by the CAA for the 'detailed examination' as required for the JAA medical. Several AME's are not capable of doing this test since they need a piece of equipment called a 'slit lamp' which is very expensive.
Find out if the optician has a pad of CAA medical forms (or ask your AME or Aviation House) and take it along for the eye exam.
Expect a pretty detailed examination including retinal inspection and glaucoma testing.
The optician will be able to assess whether the results will be sufficient for class 1 purposes. I hope this helps.