A year-old king that's otherwise healthy will be fine not eating for a few weeks. The eyes looking strange may be retained eyecaps (which will interfere with vision), or something worse. Pictures will help.
If you don't have a thermometer you do *NOT* know that the temperatures are ok, especially if you don't have it regulated by a thermostat, which you didn't mention.
First thing to do is get your husbandry correct - If you don't have a thermostat controlling your heat mat, unplug it *right* *now* and leave it unplugged until you get one. Then go look at the care sheet section for information on kings and/or milk snakes. And get a digital remote temperature "gun" thermometer so you can check temps, plus whatever else you need to add/change.
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