Your primary concern, the first item you should buy, is a face mask. Mesh goggles consist of a steel mesh which stops the BB and the only vision impairment is that the mesh makes the environment appear slightly darker. Lens masks and shooting glasses have a clear plastic viewing lens which allows greater visibility but tend to fog up during physical exertion. Thermal lenses and fan units in your goggles can reduce fogging. Not all eye protection you find in the world is BB proof so purchase eye protection rated for shooting, airsoft or paintball. Some ballistic glasses on some people’s faces will leave a gap which could let BBs in to your eye area so goggles may be preferable.
As you are probably aware, incorrect/dangerous use of an airsoft replica will easily cause catastrophic damage to eyes, but what most people don’t realise is that they will also shoot out your teeth with ease. For this reason, and to prevent unsightly hit marks on your face, you should wear a full face mask. These sometimes have goggles with integrated solid lower face protection, or you can purchase a lower face mask (often mesh) which straps to your face to compliment your goggles. You can wear a scarf or soft mask over your lower face but this may still not slow a BB enough to save your teeth. It is fashionable to wear eye protection with no lower face protection as it looks more authentic, however if you play like this for long enough then the risk of losing teeth becomes much higher and shattered teeth are not an uncommon sight at skirmishes, even though it is easy to prevent and can be extremely painful.
Also remember that you are provided with only one set of eyes – so make your safety purchases very carefully.