Completing a half marathon is a huge challenge by most people’s standards. But Cardiff man Gareth Davies won’t let anything stop him from finishing his 13.1-mile run – including sight loss. Gareth,  is taking part in the UK-wide Marathon Mates challenge this September to raise funds for sight loss charity RNIB. He will run a half marathon route around his local neighbourhood. Gareth was diagnosed with retinitis pigmentosa aged 19 and was registered blind five years ago. As a keen…