I wouldn't say that chemistry A Level uses a huge amount of maths. You need to be numerate, but there's nothing that really goes beyond maths taught at GCSE level. That said, you don't need to meet the requirements for medicine if you're planning on possibly applying to optometry, so that is a moot point
In general I recommend that, within their university subject's requirements, people pick A level subjects that they enjoy, and that they think they have the best chance of getting a good grade in. I would suggest having a look on UCAS for the entry requirements of
optometry and politics and seeing what combination of subjects would fit both optometry and politics. From quick browsing it looks as if with politics they're very flexible with the subjects you do. The only 'requirement' I found (look for longer than me, though!), has having at least one essay based subject, so Eng lit, Gov&Pol or sociology (don't worry that you didn't do it at GCSE, many people who take it for A level don't) would all be fine.