I need a new pair of specs and I've been looking online because they seem to be much cheaper than on the high street (which is another issue, how the feck can they justify charging upwards of £100 for 'designer' tiny bits of metal? Makes me sick) but I'm finding it a bit confusing.

I have different degrees of short sightedness in each eyes and I'm not sure how to go about ordering the lenses and frames and I'm worried about fucking it up and wasting my money.
Has anyone ever had a similar problem?