Hi, I am sorry his eye is not improving, a normal hay poke injury would be very much improved by now. As I mentioned before, the head tilt he had when he first injured his eye would have been a sign of pain, possibly as a result of a more penetrative injury. Sadly it seems that may be the case.
I have two of my pigs who have had these more serious kinds of injuries. Both had a head tilt in the beginning and both took a long time to heal and were left with permanent damage. It is very difficult for a vet to be able to see the extent of the damage, mainly due to the eyes natural responce to injury of turning cloudy and ulcerating. That said I would recommend taking him back to the vet as soon as possible and not wait until next week. As others have said there are stronger eye drops that may work better in his case. It is also important that he remains on the metacam.
In the case of my piggies one ended up with scarring to her eye, which my vet says means she has around 60% sight loss in that eye. In the case of the other piggy her eye kind of shrunk away. But both are perfectly fine, not in any pain and lead normal lives. Just be prepared that it may take a time for Machu's eye to resolve itself, keep going with the meds, their eyes have an amazing ability to heal even if there is some permanent loss of sight.
I will try and take some photos tomorrow but my phone is away being mended and the quality of photos using this tablet is not great and may not be enough to show details of eyes very well.