If i am not wrong, and iirc, they have different lens systems as compared to humans (or other land dwelling beings). For us, light goes from air to a lens made of "watery" substance and then through a (different) "watery" fluid in our eyes, and then to the back. whenever you have refractive index changes (air and water have different indices(water is ~1.33)), light bends, and so, the way light would refract differently, or in other words, the angle at which "focuses" (not the current optical term here, but works in a colloquial sense, angle of cone of focus would be better) is different if you have air-watery*-watery system vs water-watery*-watery system. since fish live in water mostly, they develop for the lattery system (since most of the system is water esque, there is not much refractive difference which would bend light at larger angles), so they would have to use a more "powerful" (not correct again, better would be shorter focus) lenses, or else there eyes and eye sockets would have to be large. so if they come above water, these "powerful" lenses would resolve the focus spot before the back of eye (so they would be myopic). inverse happens with land dwelling beings going in water.

Amphibians (and some other "beings") have some special "arrangements". iirc, some frogs have an extra layer of "transparent eyelid" like thingy, that they close underwater, which gives the "additiional focussing power" required to resolve.