I'm not sure there is a set of rules for Graphic Design H&S but I guess all the regs on using a computer would apply (chair positions, lenght of time looking a screen etc). Try this link, hope that is the kind of info you were looking for?
Yeah, I'd agree with Katy. DSE (Display Screen Equipment) assessments and regular eye tests would have covered it I'd have thought. Other than that it would be general office stuff (or 'common sense' as we like to call it).
If you work at home alone, you might want to check-out Lone Working.
If you work in business premises, employ others, etc, a whole different set of challenges apply. The Health & Safety Executive publish many free leaflets, there's an A-Z list here, it would be a great starting point HSE - Publications: Free Leaflets
You can also ask your local authority for advice.
I know a very down-to-earth H&S safety consultant if that's useful. I saw one of his talks, it was actually interesting and reassuring!
(The H&S Executive used to publish funny posters, well they made me laugh, "H&S Myth of the Month" - archives are here Myth of the month)