You see, apparently the main reasons behind that lack of movement is the tight fit that the eye is in their skull and the presence of a sclerotic ring. The eyes of the eagle can be as large as a humans despite them having much smaller skulls. The owls took this eye to head ratio further, to the point that the back of their eyes can be seen from the inside of their ears. Here's the skull of a harpy eagle with the sclerotic rings and an informative image about them:
Now, let's look at what makes their eyes so good:
The size of eagle eyes, disproportionately large compared to the skull, is a good reason. Bigger eyes mean more space for photoreceptors, which work in a much similar way to pixel count, the more receptors, the better the image. That's also a reason why we believe T-Rex had great eyesight, with their eyes allowing for binocular vision and being the size of oranges. Additionally, eagle eyes have a much higher number of cones than us.
2-the eye itself
Not only eagles have a convex fovea, which we assume helps them focus light better, they have two foveas in each eye (we have 2), one responsible for good monocular vision and the other for binocular vision. In addition, both their lens and cornea can change shape (we only have the lens change), allowing them for even better focusing.
They also have a pectan, but I'll elaborate that further down.
Now, regarding the dragon.
So, we want a dragon that has eagle like vision but can move its eyes around. For this answer I plan to focus on a more classic look, without the need things like tentacles in their faces or "popped out" eyes like an octopus (though I recommend looking at those, due to them having their photoreceptors inverted in relation to ours, they have no blind spots).
The main difference would have to be a large skull. If your dragons have large enough skulls, they can fit larger eyes, meaning more space for receptor cells and better vision (remember that big eyes are useless without also having brain space dealing with the information sent by them. See how eagles have such well developed brain parts regarding eyesight that they have almost no space for smell and taste). Additionally, the eye sockets will likely need to be fairly larger. See how the harpy eagle barely has space between the scleral rings and the sides of the socket. In order to have eye movement, you'll need sockets large enough to be able to contain the eyes (which might be easier to do for the eagle's more roundish eyes than for the owl's eye tubes). I would recommend keeping the rings though. Even if they are a bother to move the eyes, like the pic said, despite other important functions, they're attachment points for muscles responsible for focus, so it safe to assume they play an important role, likely in their shape changing lenses.
Lastly: circulation. One thing about managing the eye is that everything that isn't a photo reception cell in the eye means there's a place with less receptors. That's why eagles have very little bloodvessesls on their eyes (unlike us, look in the mirror and you can see the blood vessels in your eyes). This is likely possible due to a structure called pecten, which, while we don't know for sure, is assumed to be the responsible for the nutrition of their eyes without the need of bloodvessels that'd take space.
So summing up, to have a more classic-looking dragon with eagle vision, your animal will need:
eyes decently big to accommodate more photoreceptors.
a skull with large enough eyesockets in order to have space for the eyes to move around. You'll also need space to fit the muscles responsible for moving the eyes (humans need 4 groups of muscles for their eye movement ability).
convex foveas (having only one should be enough, unless you also want them to have good monocular vision).
lens and cornea capable of changing shape (likely means the need of a sclerotic ring as attachment point for some of these muscles).
special nutrition methods which allow for the lack of blood vessels in the eye (maybe a pecten).
So, yeah. You can do fine with only 2 eyes, but having them as small as possible is a no go, simply cause we can't quite shrink the structures responsible for receiving light, so to have more of them, your dragon will need to have big eyes. Additionally, as you want these already large eyes to be able to move around, you'll need even larger sockets than they'd already have with fixed eyes. The only way for you to make their eyes look smaller without reducing their capacity is making the dragon itself bigger.